chore(release): 0.8.1 — duplicate adopt/open fix + fuzz harness bookkeeping

- version 0.8.0 -> 0.8.1 (bug-fix release; semver-checks 196 pass vs 0.8.0) - CHANGELOG 0.8.1: the manager_routing-found duplicate adopt/open fix, the fuzz harness, and the verification summary - publish exclude gains docs/research/ (internal research notes; fuzz/ was already excluded — package verified clean of both) - fuzzing.md §7.9: standing no-hosted-CI policy — corpus replay is the release-verification fuzz gate; campaigns manual via the detached runner; OSS-Fuzz out; no workflow files in this repo - AGENTS.md: corpus replay added to the verification checklist - lockfiles: alkcall 0.8.1 (root + fuzz) Verification: 684 tests; clippy -D warnings (main, wasm, fuzz/shared); fmt clean; doc clean; wasm32-unknown-unknown check+clippy clean; semver-checks 196 pass; publish --dry-run 116 files (no fuzz/research/ reviews/sdd/AGENTS in the tarball); fuzz corpus replay 5/5 green
docs(research): fuzzing steps 1-3 complete; 10-min campaigns clean on all five targets
2026-09-28 06:56:11 +00:00 · 2026-09-27 23:52:45 +00:00 · 2026-09-27 23:19:18 +00:00 · 2026-09-27 21:27:58 +00:00 · 2026-09-27 21:14:35 +00:00 · 2026-09-27 20:13:35 +00:00
1502 changed files with 14336 additions and 175 deletions
@@ -194,6 +194,7 @@ Run these before committing. All must pass.

 ```bash
 cargo test                                    # full suite
+cargo test --manifest-path fuzz/shared/Cargo.toml   # fuzz corpus replay (stable)
 cargo clippy --all-targets -- -D warnings
 cargo fmt --check
 cargo doc --no-deps                           # if docs changed
@@ -215,13 +216,14 @@ cargo semver-checks check-release             # before a release
 ## Architecture Context

 - `docs/architecture/` — the authoritative spec. Read it before
-  non-trivial changes. ADRs are numbered 001..048; OQs (open questions)
+  non-trivial changes. ADRs are numbered 001..050; OQs (open questions)
  track resolved/deferred decisions.
 - This crate unifies `alknet-call` and `alknet-channels` from the
  alknet mono-repo (`/workspace/@alkdev/alknet`). The source
  architecture docs were ported from
  `/workspace/@alkdev/alknet/docs/architecture/` and renumbered as
-  alkcall ADRs (001..048; ADR-048 was authored in this crate). The ALPN
+  alkcall ADRs (001..048; ADR-049 and later were authored in this
+  crate). The ALPN
  strings (`alk/call`,
  `alk/channels`) are wire-stable going forward (renamed from
  `alknet/` to `alk/` in v0.1.1, before the first published consumer).
@@ -4,6 +4,440 @@ All notable changes to this crate are documented here. The format is
 based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/), and
 this crate adheres to [Semantic Versioning](https://semver.org/).

+## [0.8.1] - 2026-09-28
+
+Bug-fix release: a duplicate `adopt_channel`/`open_channel` no longer
+destroys the live channel it collided with, found by the crate's new
+fuzzing harness (`fuzz/` workspace — five cargo-fuzz targets, committed
+seed corpora, three 10-minute campaigns clean). No API or wire-format
+change; the error is still `Err(ChannelExists)` — the difference is
+entirely in what the collision leaves behind.
+
+### Fixed
+
+- **Duplicate adopt/open no longer replaces the live channel's state
+  (found by the `manager_routing` fuzz target,
+  `docs/research/fuzzing.md` §7.8).** `ChannelManager::open_channel`
+  and `adopt_channel` used `HashMap::insert(...).is_some()` as the
+  collision check — but `insert` *replaces* an occupied entry and
+  returns the old value, so a duplicate on an in-use id installed the
+  new `ChannelState`, dropped the live channel's `demux_sender`
+  (spurious EOF to its readers; all subsequently routed chunks lost),
+  and *still* returned `Err(ChannelExists)`. The mux write half kept
+  framing onto the transport for a channel the demux no longer fed.
+  Both functions now check `contains_key` and return before any map
+  mutation — the live channel's routing state is untouched on
+  collision. Reachable whenever an open-op response is replayed or a
+  connection-owner race re-announces an id. Regression tests:
+  `adopt_channel_duplicate_id_leaves_live_channel_intact`,
+  `open_channel_duplicate_id_leaves_live_channel_intact` (both verify
+  routing survives a rejected duplicate; the first also verifies the
+  EOF sentinel remains the only EOF source).
+
+### Added (development)
+
+- **Fuzzing harness (`fuzz/` workspace, `docs/research/fuzzing.md`).**
+  Five cargo-fuzz targets over the two attacker-reachable wire formats
+  and the stateful channel-routing surface: `chunk_header` (8-byte
+  header no-panic/round-trip/accounting), `envelope_frame` (frame
+  decode error-shape partition + allocation bound), `manager_routing`
+  (`Arbitrary` op sequences over `ChannelManager` with exact counter
+  models and the parked-bytes bound), `envelope_semantic` (all six
+  event kinds: constructors → serde → framing round-trip), and
+  `spec_parse` (attacker-shaped op-register schemas compile or reject
+  cleanly at registration). Invariant logic lives in
+  `fuzz/shared/` — a stable-toolchain crate replayed as plain
+  `cargo test`, so the committed corpora stay executable without
+  nightly. Campaigns (10 min per target, detached runner): ~25M
+  executions total, zero crashes/hangs/OOMs. The `manager_routing`
+  campaign found the 0.8.1 fix above within minutes — exactly the
+  stateful interleaving class example-based tests cannot reach.
+  `fuzz/` is excluded from the workspace and from the published
+  package.
+
+### Verified
+
+- 684 tests pass; `clippy --all-targets -- -D warnings`, `fmt --check`,
+  `cargo doc`, wasm32-unknown-unknown check, `cargo semver-checks`
+  (no API changes vs 0.8.0), and `cargo publish --dry-run` clean;
+  corpus replay (`cargo test --manifest-path fuzz/shared/Cargo.toml`)
+  green.
+
+## [0.8.0] - 2026-09-18
+
+Review 008's remediation lands in full — the graduation upstream asks
+(U-1 flavor-form open-op ids in discovery; U-2 the establisher → reply
+projection) plus the in-tree channel relay they demanded
+(`ChannelRelay`, the hub-leg install template, and the review's gate-2
+e2e harness). A post-landing audit of that diff hardened the relay's
+adopted-entry teardown and the discovery ALPN guards, corrected two
+log/error messages, and review 009's coverage debt is paid in full —
+all failure-path; no wire or API changes. The channels data plane is
+untouched (ADR-034/035's one-way doors stay closed); the new surfaces
+are additive on the call-plane JSON and the registry seams.
+
+### Added
+
+- **`Establishment` reply projection (review 008 U-2, ADR-049
+  amendment 3)** — `Establishment::with_reply_field` /
+  `with_reply_fields` / `reply_fields()` (an optional map riding the
+  typed-opaque plan carrier). The open-op wrapper merges the fields
+  into the success output after reserving `channel_id` — an
+  establisher supplying the reserved key fails loudly
+  (`channel:open_failed`, reason `handler_error`), never shadows.
+  Absent fields leave the reply byte-identical to the pre-amendment
+  shape.
+- **`ChannelClient::open_channel_with_reply` (review 008 U-2)** — the
+  full open-op success output (the extra reply fields, e.g. a
+  bind-first listener's `bound`) alongside the streams;
+  `open_channel` delegates with the fields discarded, its signature
+  unchanged.
+- **Flavor-form open-op ids in discovery (review 008 U-1, ADR-047
+  amendment 3)** — `spec_to_json_pub` emits an explicit
+  `channel_open_alpn` string alongside the boolean marker when the op
+  name is not a standard `channels/<seg>/(sub|pub)` shape (standard
+  shapes stay byte-stable); `rebuild_spec_for` prefers the explicit
+  string and generalizes the derivation to strip the LAST path
+  segment when the marker is present. `channels/tunnel/direct`-shaped
+  ops now reconstruct WITH the `channel_open` marker through
+  discovery — hubs relaying through `from_call` never see them as
+  plain forwarding stubs.
+- **`ChannelRelay` (review 008 Unit 3a, ADR-042 as amended by
+  ADR-051)** — the in-tree relay component:
+  `ProducerLeg` (`Arc<CallConnection>` + producer-leg
+  `ChannelManager` — not a `ChannelClient`, whose `take_call_
+  connection` detach is wrong for a hub with multiple connection
+  claimants) and `ChannelRelay::register_relay_openable` (registers a
+  from_call-imported marked spec on a consumer-leg registry via the
+  full open-op wrapper: ACL, per-identity cap/ledger, establishment
+  bound, teardown). The translate hop calls the producer leg with the
+  forwarded payload (`forwarded_for` from the consumer's per-call
+  identity, ADR-026 §3) and adopts the spoke-allocated id; the
+  byte-forward hop is `pump_bidi` awaited inline — the hub never
+  parses chunk framing, ids are per-connection (no rewrite exists).
+  The spoke reply's `channel_id` is stripped (the consumer reply
+  carries the hub-allocated id); the reply's other fields ride
+  through (`bound` flows end-to-end, per-hop truthful). Reason
+  mapping per ADR-051 §3 — the spoke's code and message are preserved
+  (`timeout` maps to `dial_failed`, the one non-1:1 row). The
+  adopted producer-leg channel entry reclaims when the relayed pump
+  completes. Rejection postures are loud: unmarked and Pub-typed
+  marked specs fail registration (`RelayError`), never silent stubs.
+- **`HubLegImports` + `HubLegTemplate` (review 008 Unit 3b, ADR-051
+  §5)** — the hub-leg install template as an in-tree export: the
+  `Clone` discover/stash (from_call bundles split by the marker, with
+  the per-consumer `filtered`/`only` subset filter) and the
+  `install_channel_zero` hook composing fork + generic channel ops +
+  bootstrap discovery closed over the fork (review 004 F-06) + plain
+  bundles as-is + relay openables + serving-identity resolution
+  (CF-005 precedence) + the single-stream dispatch loop. A
+  Pub-typed (or unregistrable) marked spec ends the leg's install
+  task — channel 0 never dispatches. Discovered bootstrap-discovery
+  op names are skipped on re-registration (the template's own
+  install supersedes the imported copies).
+
+### Changed
+
+- **New module `src/channels/relay.rs` and `src/channels/hub_leg.rs`
+  re-exported from `channels`**; the relay's teardown fix is part of
+  this landing (no pre-relay behavior to preserve).
+
+### Fixed
+
+Post-landing audit of the remediation diff — hardening guards,
+message corrections, and one rejection-posture fix; all failure-path.
+
+- **Adopted-entry teardown on every relay plan path** (ADR-051 §6) —
+  the relay's `RelayPlan` now owns the producer-leg
+  `ChannelManager` and reclaims the adopted spoke `channel_id` via a
+  `Drop` guard, instead of the pump handler's post-`pump_bidi`
+  explicit reclaim. This closes the leak windows the pump's normal
+  path cannot reach: the open wrapper's establishment bound expiring
+  after the adopt (the plan dropped before the pump ever spawns) and
+  the pump handler's early-return arms (plan absent, downcast
+  failure, `try_unwrap` failure, `accept_bi` failure). Dropping the
+  plan's send half still EOFs the spoke side via the mux pump's
+  implicit-EOF sentinel, so the spoke handler reclaims through the
+  same cascade as before. Regression test:
+  `relay_plan_drop_reclaims_the_adopted_producer_leg_entry`.
+- **Empty/whitespace `channel_open_alpn` rejected at rebuild** — an
+  explicit string of `""` (or whitespace-only) previously overrode a
+  sane name-derived ALPN, poisoning the marker for every consumer
+  from one misconfigured producer; `rebuild_spec_for` now trims and
+  rejects empties, falling back to the derivation.
+- **Empty-segment standard-shape names** — `channels//sub` was
+  serialized boolean-only (the standard-shape check saw flavor
+  `sub`) but reconstructed UNMARKED (the derivation's empty-segment
+  guard returned `None`) — a silent stub for a marked op. The
+  standard-shape check now applies the same empty-segment guard, so
+  the explicit `channel_open_alpn` string rides the wire and the
+  marker reconstructs.
+- **Reserved-reply-key error text and log level** — the
+  `channel:open_failed` message interpolates `RESERVED_REPLY_KEY`
+  instead of hardcoding `"channel_id"` (the two could drift), and the
+  establisher-bug log fires at `warn!` (a programming error), not
+  `debug!`.
+
+### Testing
+
+Review 009's coverage debt (all seven findings, no wire or API
+changes; three as-filed errata recorded in the review):
+
+- **C-1** — the template's plain-bundle install-failure arm is pinned
+  (un-compilable `input_schema` → the install task ends before the
+  dispatch loop, channel 0 never dispatches); ADR-051 §5 carries the
+  loud-install coverage note (relay-openable + plain-bundle arms
+  pinned; generic-ops + bootstrap-discovery arms documented as
+  best-effort-loud).
+- **C-2** — the `HubLegImports` filter: the `filtered` closure path
+  and the `only` marked/plain partition unit-tested; the empty-stash
+  e2e gate (serves only the generic ops + discovery, dropped ops
+  resolve `NOT_FOUND`).
+- **C-3** — the batch-form reserved-reply-key rejection
+  (`with_reply_fields` smuggling `channel_id`) pinned: reason
+  `handler_error`, channel torn down, ledger decremented, pump never
+  spawns.
+- **C-4** — `open_channel_with_reply`'s failure path pinned e2e: the
+  typed error carries the `channel:open_failed` code and the full
+  `details` shape (`reason` + `message`) through the new API.
+- **C-5** — both "byte-identical" claims are golden-pinned: the
+  no-fields reply against the exact `{"channel_id": 2}` literal, and
+  the standard-shape wire payload against the full 9-key literal.
+- **C-6** — the derivation's edge shapes pinned: `channels//sub` /
+  `channels//direct` / `channels` → `None`; the 4-segment strict
+  superset (`channels/x/sub/extra` → `Some("x/sub")`) annotated as the
+  pre-amendment behavior change; the verbatim `channels/alk/tty/sub`
+  case.
+- **C-7** — the builder's overwrite semantics pinned last-win (single
+  and batch forms) with the doc sentence on `with_reply_field`.
+
+### Verified
+
+- 682 tests pass (`cargo test`), `clippy --all-targets -- -D warnings`
+  and `fmt --check` clean. The gate-2 e2e harness
+  (`src/channels/gate2_tests.rs`) pins the review's gate 2: the full
+  consumer → hub → producer relay through the template (hub-allocated
+  id, `bound` surviving, data both directions with a fake 8-byte
+  chunk header riding verbatim), hub-side disconnect tearing down
+  both legs, the mid-establishment window's two reclaim signals
+  (ADR-051 §6), and the `channels/tty/sub` standard-shape companion.
+
+## [0.7.1] - 2026-09-09
+
+The MSRV floor becomes honest: `rust-version` raises from 1.85 to
+1.88. The 1.85 claim was already false at the dependency level — the
+resolved lockfile pulls icu 2.x (MSRV 1.86) and wasip2 1.87
+transitively via `jsonschema` → `idna`, so no 1.85 toolchain could
+build 0.7.0. The raise aligns with the ecosystem floor (noq's 1.88,
+matching the QUIC path) and breaks no downstream that could build the
+crate before. No API or wire-format change; downstreams on caret
+requirements pick this up on their next `cargo update`.
+
+### Changed
+
+- **`rust-version` 1.85 → 1.88.** Verified on a real 1.88 toolchain
+  (full test suite, clippy). Two clippy lints promoted since 1.85
+  were fixed to keep `-D warnings` clean on the new floor:
+  `collapsible_else_if` (`channels::mux`) and
+  `uninlined_format_args` (`core::types`,
+  `registry::registration`). Behavior-identical.
+
+## [0.7.0] - 2026-09-07
+
+The connect-side caller-identity seam (CF-005) plus the full sweep of
+every open alkcall finding from downstream consumers (CF-006, CF-007):
+a connect-side serving op can now authenticate the
+transport-authenticated peer by key-based identity (mTLS/QUIC), the
+open-op establisher/pump handler see the per-call opener identity,
+and the ADR-016 code list is current. The wire surface is unchanged.
+
+### Added
+
+- **`ServingConfig.identity: Option<Identity>` (CF-005 remediation
+  (a))** — an explicit caller identity for the connect-side serving
+  dispatch (`ChannelClient::from_connection_with_serving`). Wins over
+  the propagated transport identity; the payload `auth_token` path
+  still takes precedence over both (ADR-017 §7).
+  **Semver-relevant at 0.x:** struct literals must add
+  `identity: None`.
+- **`core::auth::NoopIdentityProvider`** — a public `IdentityProvider`
+  that resolves nothing; the identity-less posture for ACL-free
+  serving and the `ServingConfig::default()` provider (three private
+  test copies of it existed across the crate).
+
+### Changed
+
+- **The transport identity propagates to channel 0 (CF-005
+  remediation (b)).** `from_connection_with_serving` copies the
+  transport `Connection::identity()` to the channel-0 connection via
+  `set_identity` before the serving loop starts, mirroring the accept
+  side (the adapter hands the install hook the transport
+  `AuthContext`). The connect-side serving dispatch now resolves the
+  caller identity in precedence order: payload `auth_token` →
+  `ServingConfig.identity_provider`; `ServingConfig.identity`;
+  transport identity. With none, the dispatch runs identity-less and
+  `AccessControl::check` fails closed (`FORBIDDEN`) — unchanged. The
+  identity resolution is process-local (`set_identity` on the
+  internal channel-0 `Connection`); nothing new crosses the transport.
+- **The open-op establisher and pump handler see the per-call opener
+  identity (CF-006 — the CF-005 corollary).** `run_open_wrapper`
+  derives a per-call `AuthContext` — the opener's dispatch-resolved
+  identity overlaid onto the install-time context — and passes it to
+  both the establisher (ADR-049 §1) and the pump handler
+  (`OpenHandler`). Identity-less calls keep the install-time
+  identity; transport-truthful fields (`alpn`, `remote_addr`,
+  `tls_client_fingerprint`) are never rewritten. Signatures are
+  unchanged — behavior-only; on a per-connection registry (ADR-047
+  §4) this is identical to before, and on hub-forwarded opens the
+  establisher now sees the end client instead of the hub.
+- **ADR-016 amended: the protocol-code list is eight codes (CF-007 —
+  alkhttp review 006 Part C doc drift).** `ALREADY_EXISTS`
+  (non-retryable, `op/register` collision) and `CONNECTION_CLOSED`
+  (retryable, provably-undelivered call) are now in the Context
+  paragraph, the §3 table, and the `from_openapi` collision rule; §2a
+  documents the undelivered-vs-ambiguous write-failure distinction.
+  Doc-only.
+- **`ChannelPlan` type doc carries the `Send + Sync` payload
+  constraint** (alktunnels POC F-1 — a non-`Sync` boxed handle needs
+  a wrapper; documented so the next consumer doesn't re-derive it by
+  compiler error).
+- Regression gates: the four `cf005_*` tests in
+  `src/channels/client.rs` (transport propagation, override
+  precedence, identity-less failure, token fallback + precedence) and
+  the two open-op identity-overlay tests in
+  `src/channels/operations.rs`. Ledger: CF-005, CF-006, CF-007 →
+  resolved (the ledger's Open section is now empty). Specs: ADR-022
+  §connect-side-serving, ADR-016 (code list), ADR-049 establisher
+  doc note.
+
+## [0.6.0] - 2026-09-07
+
+The establishment follow-ups sweep (review 007): the `Establishment`
+plan payload lands (R-01), the `OpenHandler` lifetime contract is
+documented (R-02), and the two-pump helper is extracted (R-03). One
+breaking change (below); the wire surface is unchanged.
+
+### Added
+
+- **`pump_bidi` (review 007 R-03 / ADR-050).** The two-pump helper —
+  `channels::pump_bidi(channel, peer_read, peer_write)` — pumps a
+  channel stream (`BiStream`-shaped) against a peer's split
+  read/write halves: one pump per direction, each shutting down the
+  opposite sink on completion (alknet ADR-078's shutdown-on-
+  completion), joined, returning `(u64, u64)` copy counts. Errors
+  are EOF-shaped by design (the POC + ADR-078 semantics — no `Err`
+  state; the review sketch's `io::Result` return was dead code).
+  The helper pins the contract in one place instead of three
+  (alktunnels POC `pump_halves`, alktty's channels session, the next
+  consumer). Purely additive.
+
+### Changed
+
+- **`Establishment` carries the channel plan (review 007 R-01 —
+  breaking at 0.6.0).** The reserved field is filled:
+  `Establishment { plan: Option<ChannelPlan> }` with
+  `ChannelPlan = Arc<dyn Any + Send + Sync>` — typed-opaque, because
+  the payload an establisher hands the pump handler is a live handle
+  (a dialed socket, a TTY handle), not JSON. The wrapper threads
+  `establishment.plan` to the `OpenHandler`'s new second parameter
+  (`Fn(Value, Option<ChannelPlan>, Connection, AuthContext) ->
+  JoinHandle<()>`); `None` when no establisher is registered or it
+  returned `Establishment::default()`. Process-local: establisher →
+  wrapper → handler; nothing new crosses the transport. This kills
+  the side-channel handoff the alktunnels POC shipped (resource-keyed
+  slot + poll loop) with its concurrent same-resource race — each
+  open's establisher result flows to its own handler. Migration:
+  `Ok(Establishment {})` → `Ok(Establishment::default())` (or
+  `Establishment::new(handle)` to deliver a handle); handler closures
+  gain a `_plan` (or `plan`) parameter.
+
+- **`OpenHandler` lifetime contract documented (review 007 R-02).**
+  Doc-only semantics note on the `OpenHandler` type and the
+  registration entry points: the returned `JoinHandle` must track the
+  data-plane lifetime — the wrapper awaits it and its completion
+  triggers channel teardown (drop of the demux sender = EOF to the
+  handler's read half); a handler that returns before its pumps
+  finish tears the channel down at birth (await pumps inline, never
+  spawn-and-forget). Plus a `debug!` telemetry line in
+  `run_open_wrapper` when a handler exits without having accepted the
+  channel's `BiStream` (the birth-teardown hint).
+
+## [0.5.0] - 2026-09-06
+
+The channel-open establishment phase (ADR-049 — review 006 E-01 +
+N-1). Additive establishment machinery; one breaking change (the
+`ChannelClient::open_channel` error type, below).
+
+### Added
+
+- **`OperationSpec.description` (review 006 E-02).** Additive
+  `Option<String>` op description (builder: `with_description`),
+  disclosed by `services/list` and `services/list-peers` (local
+  listings) when set, carried in the `services/schema` wire shape
+  (`spec_to_json_pub` emit / `rebuild_spec_for` parse — the field
+  survives `from_call` discovery and `op/register` announcement).
+  Describes the op, not the produced resource set (ADR-047 §6
+  amendment: the live resource-enumeration half stays deferred,
+  OQ-40). Absent on the wire when unset — additive for all consumers.
+
+- **Channel-open establishment phase (ADR-049 — review 006 E-01).**
+  `ChannelCore::register_openable_with_establisher` registers a
+  per-ALPN open op with an establisher hook (`OpenEstablisher`): an
+  awaited establishment phase — validate params semantically, dial the
+  backend — bounded by the dispatch deadline or the registration's
+  timeout override, else `ESTABLISHMENT_TIMEOUT` (10s; the earlier of
+  the two). On establisher failure (error or deadline) the wrapper
+  tears down the just-allocated channel (demux sender, opener-ledger
+  take, `policy.on_close` un-increment — the allocation and teardown
+  balance) and replies `channel:open_failed` with
+  `details: { reason, message }`, reason ∈ `dial_failed` /
+  `unknown_resource` / `resource_shortage` / `handler_error` /
+  `timeout`. The SSH contract holds consumer-visibly: a failed open
+  never returns a `channel_id`. `register_openable` is unchanged
+  (no establisher = always-OK, existing registrations compile and
+  behave identically); the establisher takes `(input, auth)` — the
+  channel's yield-once `BiStream` belongs exclusively to the pump
+  handler. Additive wire surface (new error-code string + `details`
+  shape).
+
+### Changed
+
+- **`ChannelClient::open_channel` returns a typed error (ADR-049 §4 —
+  review 006 N-1, breaking at 0.5.0).** The open op's `CallError` is
+  carried verbatim in `ChannelOpenError::CallFailed` instead of being
+  flattened into a debug-formatted string, so consumers branch on
+  `channel:open_failed`'s typed reason (`establishment_reason()`).
+  Other variants: `MissingChannelId` (malformed success reply),
+  `AdoptFailed` (local adoption failure). Mechanical for consumers —
+  the `String` was a debug-formatting wrapper.
+
+## [0.4.1] - 2026-09-05
+
+Bug-fix release: chunks arriving for a not-yet-adopted channel are
+parked instead of dropped (the open-op response / first-data race).
+No API changes.
+
+### Fixed
+
+- **Early-arrival chunks for un-adopted channels are parked, not
+  dropped.** The connect side adopts a channel (installs local routing
+  state) only after the open-op response arrives, but the accept side's
+  `OpenHandler` can start pumping data the moment the channel opens —
+  the two race. Previously the connect side's demux dropped those
+  chunks (REQ-CH-04's lenient unknown-channel drop), silently losing
+  the first chunks of any push-first producer (a TTY backend's banner
+  or greeting, a sub protocol's initial frame). `route_payload` now
+  parks up to 64 payloads per unknown `channel_id` in a bounded
+  early-arrival buffer and `adopt_channel` drains them into the new
+  receiver in order; chunks beyond the cap drop with the pre-existing
+  debug log and `dropped_unknown_chunks` counter (the counter now means
+  "early-arrival overflow or genuinely unknown channel", not just the
+  latter). `clear_all` drops the parked buffers with the connection.
+  Surfaced by alktty's consumer end-to-end test (review #001 L3): the
+  session never resolved because the producer's first chunks (the
+  stdout sentinel + exit chunk for an immediately-resolving backend)
+  arrived before the adopt and were dropped.
+
 ## [0.4.0] - 2026-09-05

 `input_schema` is now enforced at call time (the advertise-vs-enforce
@@ -303,6 +737,14 @@ Vendored core types (`Connection`, `ProtocolHandler`, `BiStream`,
 (ADR-046), the channels protocol with openable-ALPNs-as-operations
 (ADR-047), and the `ChannelClient` transport-agnostic client.

+[0.8.1]: https://git.alk.dev/alkdev/alkcall/releases/tag/v0.8.1
+[0.8.0]: https://git.alk.dev/alkdev/alkcall/releases/tag/v0.8.0
+[0.7.1]: https://git.alk.dev/alkdev/alkcall/releases/tag/v0.7.1
+[0.7.0]: https://git.alk.dev/alkdev/alkcall/releases/tag/v0.7.0
+[0.6.0]: https://git.alk.dev/alkdev/alkcall/releases/tag/v0.6.0
+[0.5.0]: https://git.alk.dev/alkdev/alkcall/releases/tag/v0.5.0
+[0.4.1]: https://git.alk.dev/alkdev/alkcall/releases/tag/v0.4.1
+[0.4.0]: https://git.alk.dev/alkdev/alkcall/releases/tag/v0.4.0
 [0.3.1]: https://git.alk.dev/alkdev/alkcall/releases/tag/v0.3.1
 [0.3.0]: https://git.alk.dev/alkdev/alkcall/releases/tag/v0.3.0
 [0.2.0]: https://git.alk.dev/alkdev/alkcall/releases/tag/v0.2.0
@@ -27,7 +27,7 @@ dependencies = [

 [[package]]
 name = "alkcall"
-version = "0.4.0"
+version = "0.8.1"
 dependencies = [
 "async-trait",
 "bytes",
@@ -1,15 +1,19 @@
 [package]
 name = "alkcall"
-version = "0.4.0"
+version = "0.8.1"
 edition = "2021"
-rust-version = "1.85"
+rust-version = "1.88"
 license = "MIT OR Apache-2.0"
 description = "Call + channels RPC: structured JSON operations, streaming subscriptions, service discovery, and N-channel multiplexing over one transport stream"
 readme = "README.md"
 repository = "https://git.alk.dev/alkdev/alkcall"
 keywords = ["rpc", "json-rpc", "multiplexing", "wire-format", "alpn"]
 categories = ["network-programming", "asynchronous", "encoding"]
-exclude = [".opencode/", "AGENTS.md", "docs/reviews/", "docs/sdd_process.md"]
+exclude = [".opencode/", "AGENTS.md", "docs/reviews/", "docs/sdd_process.md", "docs/research/", "fuzz/"]
+
+[workspace]
+members = ["."]
+exclude = ["fuzz"]

 [lib]
 name = "alkcall"
@@ -120,6 +120,7 @@ let client = ChannelClient::from_connection_with_serving(
    Some(ServingConfig {
        registry: Arc::clone(&registry),
        identity_provider: provider,
+        identity: None, // peer identity: transport `Connection::set_identity` propagates
    }),
 ).await?;
 // peer-callable ops resolve against `registry` on channel 0;
@@ -13,7 +13,7 @@ This crate unifies `alknet-call` and `alknet-channels` from the alknet
 mono-repo, plus the vendored core types formerly in `alknet-core`. The
 source architecture docs were ported from
 `/workspace/@alkdev/alknet/docs/architecture/` and renumbered as alkcall
-ADRs (ADR-001..045). The ALPN strings (`alk/call`, `alk/channels`)
+ADRs (ADR-001..051). The ALPN strings (`alk/call`, `alk/channels`)
 are wire-stable and unchanged — see ADR-004.

 ## Documents
@@ -101,6 +101,9 @@ are wire-stable and unchanged — see ADR-004.
 | [046](decisions/046-publish-operation-type-and-handler-kind-sink.md) | Publish Operation Type and HandlerKind::Sink | `OperationType::Pub` (producer→consumer streaming); `SinkHandler` + `HandlerKind::Sink`; `call.published` wire event; `invoke_sink()` dispatch; `Subscription` renamed to `Sub` |
 | [047](decisions/047-openable-alpns-are-operations.md) | Openable ALPNs Are Operations | `channel/open` dissolves into per-ALPN ops `channels/<alpn>/sub`/`pub`; `channel_open` marker on `OperationSpec`; `ChannelCore` wrapper; extension-trait `ChannelOperationEnv`; connection-owner allocates `channel_id`; opener ledger (Gap 2 fix); ALPNs are call apps |
 | [048](decisions/048-dispatch-spine-gateway-module.md) | Dispatch Spine (feature-gated `gateway` module) | `alkcall::gateway` behind the `gateway` feature; `GatewayDispatch` invoke spine (deadline knob, re-rooted context) + `schema_disclosure_denial` (FORBIDDEN for ACL deny, spec-404 for Internal); promoted from alkhttp for hub/spoke reuse |
+| [049](decisions/049-channel-open-establishment-phase.md) | Channel-Open Establishment Phase | `OpenEstablisher` + `register_openable_with_establisher` (awaited, bounded); typed `channel:open_failed` with `details.reason`; `Establishment.plan` (`ChannelPlan`) threaded to the `OpenHandler` (amendment 2); the `JoinHandle` data-plane lifetime contract |
+| [050](decisions/050-pump-bidi-two-pump-helper.md) | `pump_bidi` Two-Pump Helper | `channels::pump_bidi` — shutdown-on-completion two-pump data plane pinned in one place (alknet ADR-078) |
+| [051](decisions/051-channel-relay-and-hub-leg.md) | In-Tree Channel Relay (`ChannelRelay`) and the Hub-Leg Assembly | ADR-042 amended — the relay implementation is an alkcall export; translate hop = ADR-049 establisher (`register_relay_openable`), byte-forward hop = `pump_bidi`; implicit per-channel id mapping; two-phase registration (discover/stash → fork-register); hub-leg install template; ACL layering note |

 ## Relevant Open Questions

@@ -272,7 +275,7 @@ feature flags) or in the downstream alknet crate.

 - `@alkdev/alknet: docs/architecture/` — the source architecture docs
  these were ported from (renumbered from alknet ADR-001..094 to alkcall
-  ADR-001..045)
+  ADR-001..048; ADR-049 and later were authored in this crate)
 - `@alkdev/alktype` — the binary struct engine; compiles BAST documents
  (e.g. `chunk-header.bast.json`) into readers/writers/validators
 - `@alkdev/pubsub` — the TypeScript EventEnvelope prior art the call
@@ -288,5 +291,5 @@ feature flags) or in the downstream alknet crate.
 > TTY's wire format, ADR-082 for alknet-tls, ADR-086 for endpoint types).
 > These are ADRs for sibling crates that are not part of alkcall. They
 > retain their alknet numbering (052, 082, 086, etc.) — any ADR number
-> outside the alkcall range 001..045 is an alknet source ADR, found at
+> outside the alkcall range 001..048 is an alknet source ADR, found at
 > `/workspace/@alkdev/alknet/docs/architecture/decisions/`.
@@ -68,12 +68,19 @@ impl ChannelClient {
    /// the `MpscRecvStream` (read half). The caller can build a
    /// `Connection` from these via `channel_source` and
    /// `Connection::from_source`.
+    ///
+    /// The error is typed (ADR-049 §4 — review 006 N-1):
+    /// `ChannelOpenError::CallFailed` carries the wire `CallError`
+    /// verbatim (branch on `establishment_reason()` for
+    /// `channel:open_failed`'s `details.reason`); `MissingChannelId`
+    /// covers a malformed success reply; `AdoptFailed` covers local
+    /// adoption failure.
    pub async fn open_channel(
        &self,
        operation_id: &str,
        input: Value,
        alpn: &str,
-    ) -> Result<(u32, MpscSendStream, MpscRecvStream), String>;
+    ) -> Result<(u32, MpscSendStream, MpscRecvStream), ChannelOpenError>;

    /// Take the `CallConnection` — used by the consumer to register
    /// imported ops (`from_call`) on the connection's overlay. After
@@ -88,7 +95,11 @@ impl ChannelClient {
 ADR-047 dissolved the generic `channel/open` operation into per-ALPN
 open ops (`channels/<alpn>/sub`, `channels/<alpn>/pub`). Each ALPN
 crate registers its own open op via `ChannelCore::register_openable`
-(ADR-047 §3, as amended 2026-08-13 — per-connection registration).
+(ADR-047 §3, as amended 2026-08-13 — per-connection registration),
+optionally with an establisher via
+`register_openable_with_establisher` (ADR-049 — the awaited,
+bounded establishment phase; establishment failure resolves
+`Err` on the client with `channel:open_failed` + `details.reason`).
 The `ChannelClient` calls these ops by name on channel 0 via
 `call_open_op`; `open_channel` wraps `call_open_op` + `adopt_channel`.

@@ -97,6 +108,35 @@ and `subscribe_resources` method are deferred (OQ-40, OQ-41). The
 `ResourceEntry.access` preview was dropped by ADR-047 §6 — it is
 available via `services/schema` on the op spec.

+## The early-arrival park bound (push-first producers)
+
+The open-op response carrying `channel_id` races the producer's first
+data-plane writes: the producer's handler can start pumping before the
+consumer's `adopt_channel` runs. The demux parks those first chunks
+per-channel (FIFO) instead of dropping them, and `adopt_channel` drains
+the parked chunks into the new receiver — a push-first producer (a TTY
+backend's banner, a sub protocol's greeting) must not lose its first
+chunks.
+
+The park is bounded: **up to 64 chunks per channel** are parked
+(`EARLY_ARRIVAL_CAP`, ADR-040's memory bounds); chunks arriving past
+the cap are dropped silently — at the consumer this presents as a
+truncated stream with clean framing everywhere else, not as an error.
+Consumer-facing consequences (review 006 E-04, noted for tunnel-style
+consumers):
+
+- Size any pre-adopt buffering math (e.g. a UDP POC's MTU-vs-buffer
+  sizing) against **64 parked chunks as the observable bound**, and
+  adopt promptly — the open reply resolves *before* the first data
+  arrives by design, so the adopt is the consumer's next step, not a
+  slow path.
+- The producer side observes both halves of the race via
+  `ChannelManager::early_arrival_count()` (chunks parked) and
+  `ChannelManager::dropped_unknown_chunks()` (chunks lost to the cap) —
+  a non-zero dropped counter under a push-first producer means the
+  adopter was too slow for the producer's burst, and the affected
+  streams were truncated at the park boundary.
+
 ## Transport-agnostic by construction

 `ChannelClient` is the client side of the channels protocol. The channels
@@ -77,12 +77,39 @@ round-trip, so the open round-trip is not additive latency.
 | `channel:forbidden` | `AccessControl::check` denied the open | false |
 | `channel:allocation_failed` | Handler allocate failed (e.g., backend couldn't start) | true (often transient) |
 | `channel:too_many_channels` | Per-connection or per-identity channel limit hit (ADR-040, ADR-041) | false |
+| `channel:open_failed` | The establishment phase failed (ADR-049) — `details: { reason, message }`, reason ∈ `dial_failed` / `unknown_resource` / `resource_shortage` / `handler_error` / `timeout` | false |
 | `channel:no_channels_session` | The op was invoked outside a channels session (no `ChannelManager` — ADR-047 §2) | false |

 `channel:unknown_alpn` and `channel:invalid_params` (ADR-037) are gone —
 an unregistered ALPN is an ordinary `NOT_FOUND` (op not registered); a
 bad `input` is ordinary schema rejection.

+### The establishment phase (ADR-049)
+
+An openable ALPN may register an **establisher** alongside its open
+handler (`ChannelCore::register_openable_with_establisher`). The
+establisher is the awaited preparation step ADR-047 §3 described
+("validate params, consult ownership, prepare the backend, return a
+channel plan"): the wrapper awaits it **bounded** (the dispatch
+deadline when the op carries one, else the registration's override or
+the 10s `ESTABLISHMENT_TIMEOUT` — the earlier of the two), **before
+replying and before spawning the pump handler**. On establisher
+failure (error or deadline) the wrapper tears down the just-allocated
+channel (demux sender, opener-ledger entry, `policy.on_close`
+un-increment — the same atomic ledger-take gate every teardown path
+runs) and replies `channel:open_failed` with
+`details: { reason, message }` (the table row above). The SSH
+contract holds consumer-visibly: a failed open never returns a
+`channel_id`.
+
+Registrations without an establisher behave exactly as before (the
+open op cannot fail post-allocation; establishment work inside the
+handler is invisible to the open reply). The bound applies only to
+the establisher — the spawned pump handler's lifetime is governed by
+the existing teardown machinery, unchanged. Head-of-line safety: the
+serving loop spawns Once invocations as independent tasks, so a slow
+establisher on one open op does not block other calls on channel 0.
+
 ### `channels/<alpn>/pub` — publish a binary stream

 `OperationType::Pub` (ADR-046). The initiator publishes a stream of
@@ -443,6 +470,8 @@ All design decisions are documented as ADRs in [decisions/](decisions/).
 | [035](decisions/035-channels-pure-channel-multiplexing.md) | Pure Channel Multiplexing | No stream_types; handler owns sub-mux |
 | [021](decisions/021-streaming-handler-for-subscriptions.md) | StreamingHandler | The machinery `channel/resources/subscribe` uses |
 | [046](decisions/046-publish-operation-type-and-handler-kind-sink.md) | Pub Operation Type | The `Pub`/`Sub` primitives the per-ALPN open ops build on |
+| [049](decisions/049-channel-open-establishment-phase.md) | Channel-Open Establishment Phase | The establisher hook; typed `channel:open_failed`; `Establishment.plan` (amendment 2); the `JoinHandle` lifetime contract |
+| [050](decisions/050-pump-bidi-two-pump-helper.md) | `pump_bidi` Two-Pump Helper | The data-plane helper openable-ALPN handlers await inline |
 | [026](decisions/026-forwarded-for-identity.md) | Forwarded-For Identity | The auth chain for hub-relayed opens (and why the cap is per direct-caller, not per `forwarded_for`) |
 | [011](decisions/011-dynamic-resource-ownership-for-runtime-spawned-resources.md) | Dynamic Resource Ownership | The parallel — a channel slot is a resource, the cap is a quota check; `resource_id_path` works again under per-ALPN ops |

@@ -450,6 +479,9 @@ All design decisions are documented as ADRs in [decisions/](decisions/).

 - ADR-047: openable ALPNs are operations (the unifying ADR — per-ALPN
  open ops, `channel_open` marker, `ChannelCore` wrapper, opener ledger)
+- ADR-049: channel-open establishment phase (the establisher hook,
+  `channel:open_failed`, the plan payload)
+- ADR-050: `pump_bidi` (the two-pump helper)
 - ADR-037: channel lifecycle operations (amended by ADR-047)
 - ADR-041: per-identity channel cap (amended by ADR-047 §7 — opener
  ledger, every teardown path)
@@ -2,23 +2,30 @@

 ## Status

-Accepted (amended by ADR-021 — protocol-level code list extended to six)
+Accepted (amended by ADR-021 — protocol-level code list extended to six;
+amended 2026-09-07 — extended to eight, see §2a below)

 ## Context

 The `OperationSpec` in alknet-call has `input_schema` and `output_schema` but
 no `error_schemas`. The `call.error` payload (call-protocol.md L128–134)
-carries a `code` and `message`, where `code` is one of six infrastructure
+carries a `code` and `message`, where `code` is one of eight infrastructure
 codes: `NOT_FOUND`, `FORBIDDEN`, `INVALID_INPUT`, `INVALID_OPERATION_TYPE`,
-`INTERNAL`, `TIMEOUT`.
+`INTERNAL`, `TIMEOUT`, `ALREADY_EXISTS`, `CONNECTION_CLOSED`.

-These six codes cover **protocol-level failures** — the call protocol
+These eight codes cover **protocol-level failures** — the call protocol
 itself can always fail to find an operation, deny access, reject bad input,
-reject the wrong dispatch method for the operation type, time out, or hit
-an internal error. They are emitted by the dispatch machinery (the registry,
+reject the wrong dispatch method for the operation type, time out, hit an
+internal error, reject a registration collision, or report a provably
+undelivered call. They are emitted by the dispatch machinery (the registry,
 the adapter), not by operation handlers. `INVALID_OPERATION_TYPE` was added
 by ADR-021 (streaming handler for subscriptions — `invoke()` called on a
 `Subscription`, or `invoke_streaming()` on a `Query`/`Mutation`).
+`ALREADY_EXISTS` was added by the ADR-022 collision sub-amendment
+(2026-09-04 — `op/register` rejects a peer-announce collision; non-retryable,
+registration is state). `CONNECTION_CLOSED` was added by the consumer
+findings ledger CF-001 (2026-08-30 — write failures on provably undelivered
+`call.requested` frames; **retryable** — see §2a).

 But operations also have **domain-level failures** that are not covered:

@@ -186,7 +193,7 @@ optional-array convention.

 ### 3. Protocol-level vs operation-level error codes

-The six existing codes are **protocol-level** — emitted by the dispatch
+The eight existing codes are **protocol-level** — emitted by the dispatch
 machinery, not by handlers:

 | Code | Emitted by | Meaning |
@@ -197,6 +204,20 @@ machinery, not by handlers:
 | `INVALID_OPERATION_TYPE` | Registry / `OperationEnv` | Wrong dispatch path for the operation's type (`invoke()` on a `Subscription`, `invoke_streaming()` on a `Query`/`Mutation`, or `OperationEnv::invoke()` on a `Subscription` during composition — ADR-021) |
 | `INTERNAL` | Registry / Adapter | Handler panic, unhandled error, connection failure |
 | `TIMEOUT` | Adapter | Request timed out |
+| `ALREADY_EXISTS` | Registry (`op/register` collision gate) | A peer-announce or import collides with an existing registration (`replace: false`, or a serving-side name — ADR-022). Non-retryable without `replace: true`. |
+| `CONNECTION_CLOSED` | Client write path | The `call.requested` frame could not be written — the call is provably undelivered (CF-001). `retryable: true` — the only protocol code a caller may auto-retry. Mid-publish and completed-frame write failures stay `INTERNAL` (delivery ambiguous). |
+
+#### 2a. `CONNECTION_CLOSED` — the retryable undelivered-call code (CF-001)
+
+The write-failure mapping distinguishes **provably undelivered** from
+**delivery-ambiguous**: a failed write of the *request* frame means the
+producer never saw the call — reconnect/retry is safe. A failed write
+*after* delivery started (mid-publish, completed frame) is ambiguous —
+retry unsafe — and stays `INTERNAL`. The producer-side `fail_all(...)` on
+connection close also stays `INTERNAL` (the callee cannot know what the
+caller received). The code is additive to the wire vocabulary; consumers
+treat unknown codes per their existing policy, with the `retryable` flag
+as the machine-readable signal.

 Operation-level domain codes are emitted by **handlers** — the operation's
 own logic determines what went wrong. They are declared in `error_schemas`
@@ -247,9 +268,9 @@ accordingly.
 ```

 **Normative rule (review #002 W20)**: `from_openapi` must not produce error
-codes that collide with the six protocol-level codes (`NOT_FOUND`,
+codes that collide with the protocol-level codes (`NOT_FOUND`,
 `FORBIDDEN`, `INVALID_INPUT`, `INVALID_OPERATION_TYPE`, `INTERNAL`,
-`TIMEOUT`). The adapter prefixes
+`TIMEOUT`, `ALREADY_EXISTS`, `CONNECTION_CLOSED`). The adapter prefixes
 imported error codes with `HTTP_` and the status number (e.g., `HTTP_404`,
 `HTTP_429`) to avoid collision. This is a requirement for the adapter, not
 a naming convention — the `from_openapi` example above was previously shown
@@ -410,6 +431,10 @@ enum instead of a generic `Result<Output, string>`.
 - ADR-021: Streaming handler for subscriptions (amends this ADR's
  protocol-level code list — `INVALID_OPERATION_TYPE` added as the sixth
  protocol-level code)
+- ADR-022 (collision sub-amendment 2026-09-04): `ALREADY_EXISTS` — the
+  `op/register` collision rejection code
+- Consumer findings ledger CF-001 (2026-08-30): `CONNECTION_CLOSED` —
+  the retryable provably-undelivered-call code
 - docs/sdd_process.md L19, L423 (Safe Exit protocol — the general principle
  of making failure typed and declared)
 - TypeScript reference: `/workspace/@alkdev/operations/src/types.ts`
@@ -402,12 +402,32 @@ surfaces discovery failure as `AdapterError::DiscoveryFailed`).
 `ChannelClient::from_connection_with_serving(connection,
 Option<ServingConfig>)` — with `None` (the pure-consumer default) the
 read pump resolves outbound pendings only (previous behavior). With
-`Some(ServingConfig { registry, identity_provider })` the read pump
-becomes the full-duplex serving loop (`Dispatcher::serve_single_stream`):
-inbound `call.requested` frames dispatch against the configured
-registry and resolve back to the peer; outbound pendings still resolve
-in the same loop. Serving is opt-in because a pure consumer has no
-registry to serve; the *protocol* is symmetric, the *API* is explicit.
+`Some(ServingConfig { registry, identity_provider, identity })` the
+read pump becomes the full-duplex serving loop
+(`Dispatcher::serve_single_stream`): inbound `call.requested` frames
+dispatch against the configured registry and resolve back to the peer;
+outbound pendings still resolve in the same loop. Serving is opt-in
+because a pure consumer has no registry to serve; the *protocol* is
+symmetric, the *API* is explicit.
+
+**Caller identity for the serving dispatch (CF-005, 2026-09-07).**
+`from_connection_with_serving` builds channel 0 internally, so before
+the remediation there was no capture point for the
+transport-authenticated peer: the serving dispatch resolved identity
+only from the payload `auth_token`, and a scope-gated serving op could
+not authenticate a key-based (mTLS/QUIC) peer by transport identity.
+The remediation makes the identity resolution, in precedence order:
+(1) the payload `auth_token` → `ServingConfig.identity_provider`
+(hub-forwarding and browser-token path, ADR-017 §7); (2) the
+`ServingConfig.identity` override (explicit, e.g. an
+assembly-layer-resolved principal); (3) the transport connection's
+identity, propagated automatically — `from_connection_with_serving`
+copies `connection.identity()` onto the channel-0 connection via
+`set_identity` before the serving loop starts, mirroring the accept
+side, where the adapter hands the install hook the transport
+`AuthContext` and the hook sets the channel-0 identity. With no
+identity from any path the dispatch runs identity-less and
+`AccessControl::check` fails closed (`FORBIDDEN`).

 Direction disambiguation in the loop is by table membership, not
 framing: an id that is one of *our* outbound pendings resolves there;
@@ -2,7 +2,52 @@

 ## Status

-Accepted
+Accepted (amended 2026-09-17, ADR-051 — the relay implementation is an
+alkcall export (`ChannelRelay`), not downstream-only code; the §"Scope
+note" below is revised, and the §`channel_id` mapping / close-translation
+mechanism is superseded by an implicit-per-channel shape — see
+"Amendment (ADR-051, in-tree relay export, 2026-09-17)" below;
+the translate-not-forward contract and the auth-model rationale are
+unchanged)
+
+## Amendment (ADR-051, in-tree relay export, 2026-09-17)
+
+The relay implementation moved into alkcall as a reusable export
+(`ChannelRelay`, ADR-051) — consumers that exist (alktunnels'
+graduation, alkhttp's fallback hub, alknodes) all need the same shape,
+so the §"Scope note" decision ("the relay implementation lives in
+`alknet-hub`/downstream") is revised: hub crates COMPOSE the export.
+
+Two implementation findings supersede mechanism text above, both
+within the two-way door this ADR already marked:
+
+1. **The `channel_id` mapping dissolves.** §`channel_id` mapping
+   pinned a `HashMap<channel_id, channel_id>` per (browser, spoke)
+   pair. The implementation needs no map: each leg's `ChannelManager`
+   holds its own id → routing state, and the per-channel pump closure
+   binds both legs. The mapping is implicit-per-channel — a
+   `channel_id` never crosses legs, so the translate hop produces
+   per-leg-truthful ids (this also refines alktunnels ADR-008 §Hub
+   re-produce's "re-map the id at their re-produce hop naturally":
+   the re-map is two independent allocations, not a rewrite).
+2. **`channel/close` needs no translation surface.** The §mapping
+   bullet's "On `channel/close` (translated the same way), the mapping
+   is removed" assumed the map; without it, close propagates through
+   the EOF cascade (consumer-side close → open-op wrapper teardown →
+   pump abort → send-half drop → EOF chunk → spoke handler exits →
+   spoke's own wrapper decrements its ledger) with correct accounting
+   on both legs. The hub never sees a `channel/close` to translate.
+   `channel/control` stays per-leg (OQ-39 — a hub wanting cross-leg
+   control translation composes it downstream), unchanged.
+
+The byte-forward layer is ADR-050's `pump_bidi` per channel (the
+hub never parses chunk framing — stronger than §"Data-channel layer"'s
+rewrite phrasing, which assumed the map-based rewrite shape). The
+translate layer is the ADR-049 establisher shape
+(`register_relay_openable`), keeping the consumer leg's full wrapper
+machinery (registry ACL, per-identity cap/ledger, establishment bound,
+teardown-on-failure) — the auth-model rationale above is unchanged and
+now has a concrete in-tree carrier.

 ## Context

@@ -8,7 +8,128 @@ Accepted (amends ADR-037; refines ADR-044, ADR-046; §4 amended
 registration, 2026-08-13)"; amendment #2 (2026-09-03) — the
 per-connection registration mechanism is the **per-session fork of the
 base registry installed as the session's dispatch registry**, not the
-connection overlay — see "Amendment (§4 mechanism, 2026-09-03)" below)
+connection overlay — see "Amendment (§4 mechanism, 2026-09-03)" below;
+§6 amended 2026-09-06 — the static half of discovery gains an additive
+per-op `description` on the listing, the dynamic half stays deferred
+— see "Amendment (§6 listing enrichment, 2026-09-06)" below;
+amendment 3 (2026-09-16, review 008 U-1) — the op-name convention
+extends to the flavor form and discovery carries an explicit
+`channel_open_alpn` for non-derivable names — see "Amendment 3" below)
+
+## Amendment 3 (flavor-form open-op ids + explicit `channel_open_alpn`, 2026-09-16 — review 008 U-1)
+
+alktunnels' graduation (ADR-002 Amendment 1 at
+`/workspace/@alkdev/alktunnels/docs/architecture/decisions/002-alpn-strategy.md`)
+pins two NEW `Sub`-typed open ops on the existing `alk/tunnel` ALPN
+with flavor-form op ids (`channels/tunnel/direct`,
+`channels/tunnel/forwarded`) — the ssh
+`direct-tcpip`/`forwarded-tcpip` shape: one ALPN, several channel
+flavors, one open op per flavor. §1 pinned the open-op naming to
+exactly two shapes per ALPN (`channels/<alpn>/sub`,
+`channels/<alpn>/pub`), and Gap F's marker reconstruction derived the
+ALPN by stripping exactly those two suffixes — so a flavor-form op id
+failed the derivation and a hub consuming through discovery rebuilt
+the spec WITHOUT the marker (the silent plain-forwarding-stub failure,
+the worst mode for a relay). Runtime was never blocked (registration
+sets the ALPN explicitly; `open_channel` takes it as an argument);
+discovery + hub relay are the re-produce path that must survive.
+
+**The convention sentence (mirroring alktunnels ADR-002 Amendment 1):**
+`channels/<alpn>/<flavor>` is a valid open-op name where `<flavor>`
+is a bare path segment (no `/`), `Sub`-typed, served through the same
+establishment wrapper and relay path as `…/sub`. New flavors are new
+op ids — additive; the `…/sub` op is never reused for a different
+meaning. `OperationType` (`Sub`/`Pub`) continues to carry the
+direction; the flavor is the channel-type discriminator the producing
+crate owns (per-ALPN params semantics, per alktunnels ADR-001
+Amendment 1).
+
+**The wire shape (Gap F refinement):** the boolean marker's
+round-trip is derivable only for the standard shapes. The rule:
+
+- `spec_to_json_pub` keeps emitting `"channel_open": true` for every
+  marked op (unchanged). When the op name is NOT the standard
+  `channels/<segment>/(sub|pub)` shape, it ALSO emits
+  `"channel_open_alpn": "<alpn>"` — the explicit string rides beside
+  the boolean. Standard shapes stay byte-identical to the
+  pre-amendment payload (no new key).
+- `rebuild_spec_for` prefers the explicit string when present; else
+  (the boolean alone — the deployment-skew case of an old producer)
+  the derivation generalizes from "strip `/sub`|`/pub`" to "strip the
+  LAST path segment." The boolean marker remains the gate: the
+  derivation is consulted only for marked ops, so a plain op named
+  `channels/tty/query` is unaffected, and a `channel_open_alpn`
+  string without the boolean never marks an op.
+- `services/schema`'s advertised `operation_spec_schema` documents
+  `channel_open_alpn` as an optional `["string", "null"]` property
+  (schema-type widening, additive — old consumers ignore unknown
+  properties).
+- Both wire consumers of the shape — the `from_call` import and the
+  `op/register` announced-spec path — parse through the same
+  `rebuild_spec_for`, so one parser change covers both.
+
+**Residual ambiguity, pinned:** an op name whose ALPN segment itself
+ends in a flavor-like name (`channels/x/direct` where the intended
+ALPN is `alk/x/direct`-shaped) is undecidable from the name alone —
+strip-last reads `alk/x`, and the true ALPN is unknowable from the
+name. The explicit `channel_open_alpn` string is the disambiguator:
+producing crates with non-`alk/*`-derivable names set it; the
+derivation is the fallback for derivable shapes. Old producers
+(alkcall ≤ 0.7.1) cannot serve flavor-form marked ops discoverably
+until upgraded — the review's one-way-door timing note.
+
+Door type: the flavor-form names and the additive
+`channel_open_alpn` key are wire-stable from the first consumer
+(alksocks composes against them); the boolean's meaning for
+standard-shape ops is unchanged (the pre-amendment byte-stability is
+pinned by test). The `op_name_is_standard_channel_open_shape` helper
+and the strip-last derivation are two-way-door implementation details
+within the one-way wire shape.
+
+Implemented surface (alkcall 0.8.0): the generalized
+`derive_alpn_from_op_name` (strip-last), the explicit-field emission
+(`spec_to_json_pub` + the advertised schema property), and the
+preference order in `rebuild_spec_for`. Verification gates landed as
+tests: `channels/tunnel/direct` reconstructs WITH
+`channel_open = alk/tunnel` (gate 1, both the explicit-string and the
+skew-case paths); standard boolean ops (`channels/tty/sub`,
+multi-segment `channels/custom/proto/sub`) round-trip byte-stable
+(gate 3); the explicit string overrides a colliding derivation; a
+string without the boolean never marks; `op/register` announced
+flavor-form specs round-trip with the marker. Gate 2 (the hub-relay
+round trip) lands with the in-tree relay component (review 008
+remediation plan Unit 3c, amending ADR-042 — the relay export is
+ADR-051).
+
+## Amendment (§6 listing enrichment, 2026-09-06)
+
+Review 006 E-02 (from the alktunnels Phase 0 sweep) made §6's dynamic
+half load-bearing for the first time and asked for a decision on the
+static half. Decision: **both halves of the "static per-op" split gain
+what is cheap today; the dynamic half stays deferred** (OQ-40, now
+with a "load-bearing for alktunnels discovery UI" note in
+`open-questions.md`; alktunnels v1 uses config-known op names):
+
+- `OperationSpec` gains `description: Option<String>` — a human-
+  readable op description, set via `with_description` at registration.
+  Additive (defaults `None`; no struct-literal construction sites
+  exist — all sites use `OperationSpec::new`).
+- `services/list` (and the local-ops half of `services/list-peers`)
+  emit `description` when set — one round-trip answers "which ops
+  exist and what are they for" without the N+1 `services/schema`
+  sweep. The output-schema docs on both listing specs and on
+  `services/schema`'s `operation_spec_schema` advertise the field.
+- `spec_to_json_pub` emits it when set; `rebuild_spec_for` parses it
+  back — the description survives discovery and peer announcement
+  (`from_call`, `op/register`) like every other additive spec field
+  (`resource_id_path`, `publish_schema` round-trip the same way).
+
+Scope note from E-02 stands: the listing field describes **the op**,
+not **the produced resource set** (a tunnel producer registers one op
+and N resources). "Which tunnel resources may I open, live" remains
+`channel/resources/subscribe`'s job (§6's dynamic half, ADR-037 §
+`channel/resources/subscribe`) — deferred until a consumer needs live
+resource discovery.

 ## Amendment (§4 mechanism, 2026-09-03)

@@ -0,0 +1,481 @@
+# ADR-049: Channel-Open Establishment Phase (`OpenEstablisher`)
+
+## Status
+
+Accepted — implemented in alkcall 0.5.0 (Unit 1: E-01 + N-1; see the
+"Amendment (Unit 1 implementation, 2026-09-06)" at the bottom).
+Amends ADR-047 §3 — the open-op wrapper gains an awaited
+establishment phase ahead of the spawned pump handler; resolves review
+006 E-01 and N-1. Amendment 3 (2026-09-16, review 008 U-2) adds the
+establisher reply projection — see "Amendment 3" below.
+
+## Context
+
+ADR-047 §3 made openable ALPNs operations: the ALPN crate supplies an
+open handler, and the channels wrapper does the channel machinery
+(allocation, ledger, policy, spawn). The §3 decision text describes the
+handler's job as "validate params, consult ownership, prepare the
+backend, return a 'channel plan'" — an awaited preparation step the
+wrapper consults **before** replying. The implemented `OpenHandler`
+type (`Arc<dyn Fn(Value, Connection, AuthContext) -> JoinHandle<()>`)
+collapsed that preparation into a fire-and-forget spawn: the wrapper
+collects the `JoinHandle`, records it for teardown, and writes
+`{ "channel_id": <id> }` to the wire the moment the handler task is
+*spawned* (`run_open_wrapper`, `src/channels/operations.rs`). The
+establishment phase the ADR described never became a thing the wrapper
+could consult.
+
+The consequence (review 006 E-01, verified at tree `88e3f5e`): the open
+op **cannot fail after allocation**. Any establishment failure inside
+the handler — params valid at the schema level but semantically
+rejected, backend lookup failure, a target dial refused for a
+`direct-tcpip`-shaped tunnel, a resource no longer available — is
+invisible to the open reply. The consumer observes: the call op
+succeeds with `{channel_id}`, the channel is adopted, and then the
+channel EOFs (the handler exits without writing; the mux pump writes
+the implicit-EOF chunk; `MpscRecvStream::poll_read` returns clean EOF
+for both the sentinel and sender-drop arms). A dial failure is
+byte-for-byte indistinguishable from a target that closed immediately
+after connecting — the two most different failure/success stories map
+to the same consumer-visible event.
+
+Every established tunnel/forwarding protocol puts establishment failure
+in the open reply, not in the data stream:
+
+- **SSH** (RFC 4254 §5.1): `SSH_MSG_CHANNEL_OPEN_FAILURE` is a
+  first-class reply carrying a reason code
+  (`ADMINISTRATIVELY_PROHIBITED` / `CONNECT_FAILED` /
+  `UNKNOWN_CHANNEL_TYPE` / `RESOURCE_SHORTAGE`) plus a description
+  string; the channel never exists on the opener's side afterward.
+- **SOCKS5** (RFC 1928 §6): the reply carries REP codes 0x01–0x08;
+  error-then-close, never "success then in-stream error."
+- **udpgw** (tun2proxy) is the counterexample: an opaque ERR bit with
+  zero reason information — the vocabulary to avoid.
+
+The per-crate workaround proves the gap is load-bearing: alktty's
+channels path answers establishment failures with a length-prefixed
+JSON error frame **on the channel stream**
+(`send_negotiation_error`, `alktty/src/adapter.rs`), disambiguated from
+data by a `0x00` first-byte peek. That is a per-crate reinvention of a
+protocol-level capability every ALPN crate will need: a structured,
+typed, **establishment-failure reply to the open op**. It also forces
+the phantom-opened channel to exist in the manager — allocation, ledger,
+and policy all fire for a channel that never carries data.
+
+alktunnels (the next consumer, arbitrary TCP/UDP tunnels over channels)
+hits this on day one: its producer dials the tunnel target inside the
+open op, and dial failure is the *common* case, not the edge case
+(review 006 E-01; alktunnels OQ-TN-09).
+
+This is the cheapest moment to fix upstream: three downstream crates
+(alktty, alkhttp, alktunnels-in-progress), alkcall 0.4.x, no published
+consumer depends on the phantom-open shape.
+
+## Decision
+
+### 1. The open-op wrapper gains an awaited establishment phase
+
+`ChannelCore::register_openable` accepts an optional
+**establisher** alongside the existing `OpenHandler`:
+
+```rust
+/// The establishment result. `Establishment` carries what the
+/// pump phase needs (today: nothing — reserved for a channel plan).
+/// `EstablishmentError` carries the reason code + message the
+/// wrapper puts in the open reply's `details`.
+pub type OpenEstablisher = Arc<
+    dyn Fn(Value, Connection, AuthContext)
+        -> BoxFuture<'static, Result<Establishment, EstablishmentError>>
+        + Send
+        + Sync,
+>;
+```
+
+The establisher is **awaited by the wrapper, bounded** — before the
+reply is written, before the pump handler is spawned. The pump handler
+(the existing `OpenHandler`, unchanged) is spawned only on
+establishment success. The dial is the natural establisher step for
+tunnels; the pumps remain the spawned handler. This restores ADR-047
+§3's original "channel plan" shape: the establisher is the awaited
+preparation, the wrapper consults its result, the pumps are the
+spawned protocol.
+
+**Why split-hook, not await-and-inspect** (the two candidates review
+006 proposed):
+
+- The split preserves the `OpenHandler` type exactly. Await-and-inspect
+  changes `OpenHandler`'s return type (`JoinHandle<()>` →
+  `JoinHandle<OpenResult>`), breaking all three consumers' handlers and
+  the alkhttp `OpenableAlpn` ferry for no compensating gain.
+- Establishment and pump are genuinely different lifecycles. The dial
+  is synchronous with the open reply (SSH's semantics: the failure is
+  the open's reply); the pumps outlive the reply. Coupling the
+  establishment signal to the pump task's lifecycle (watching a
+  `JoinHandle` for a first resolution) conflates them and makes the
+  "established, continue" signal an out-of-band convention (a sentinel
+  `Result` value, a oneshot the handler must remember to signal) —
+  more protocol per crate, the thing this fix exists to remove.
+- The split is backward compatible by construction: no establisher
+  registered = an always-OK establisher. Existing registrations compile
+  and behave unchanged.
+
+### 2. The deadline bounds the establisher, not the pumps
+
+The establisher await is bounded by the dispatch deadline when the
+`OperationContext` carries one (`context.deadline`), else by a crate
+constant (`ESTABLISHMENT_TIMEOUT`, 10s default; overridable per
+registration via a `Duration` argument on the establisher-taking
+`register_openable` variant). On deadline expiry the wrapper treats it
+as establishment failure with reason `timeout`.
+
+The bound applies **only** to the establisher. The spawned pump
+handler's lifetime is governed by the existing teardown machinery
+(`channel/close`, connection drop, handler exit) — unchanged.
+
+Head-of-line safety is already proven: the serving loop spawns Once
+invocations as independent tasks
+(`Dispatcher::spawn_once_dispatch`), so a slow establisher on one open
+op does not block other calls on channel 0.
+
+### 3. Establishment failure: teardown + typed `channel:open_failed`
+
+On establishment failure (error or deadline), the wrapper:
+
+1. Tears down the just-allocated channel
+   (`teardown_channel` — drops the demux sender, returns the not-yet-
+   installed handler task handle if any),
+2. Takes the opener-ledger entry and calls `policy.on_close(opener)`
+   (the same un-increment path the allocation-failure arms already
+   run — the ledger `take` is the atomic gate, ADR-047 §7),
+3. Replies with a new typed error:
+
+```
+code:     "channel:open_failed"
+message:  human-readable establishment failure description
+retryable: false
+details:  { "reason": <reason-code>, "message": <detail string> }
+```
+
+The reason-code vocabulary maps 1:1 onto what an establisher can
+actually produce (per the SSH four; the survey's finding):
+
+| reason | meaning |
+|---|---|
+| `dial_failed` | the backend/target could not be reached or refused |
+| `unknown_resource` | the requested resource does not exist |
+| `resource_shortage` | the backend is out of capacity (ports, fds, slots) |
+| `handler_error` | establisher-internal failure not covered above |
+| `timeout` | establishment exceeded the deadline |
+
+Policy denial stays `channel:too_many_channels` (pre-allocation,
+unchanged); ACL denial stays `FORBIDDEN` (registry gate, unchanged).
+The new code is an additive wire addition (new error-code string +
+optional `details` shape); no existing consumer breaks. ALPN crates'
+open-op specs gain matching `ErrorDefinition` entries per ADR-016 so
+`services/schema` discloses the failure contract.
+
+The SSH "channel never exists opener-side" property is the contract:
+the consumer's open resolves `Err` and no `channel_id` was ever
+returned. (The allocation still happened accept-side momentarily —
+that is invisible to the consumer and is what the teardown in step 1
+cleans up.)
+
+### 4. `ChannelClient::open_channel` stops erasing the error (review 006 N-1)
+
+`ChannelClient::open_channel` currently flattens the `CallError` into a
+`String` (`format!("open op failed: {e:?}")`), which would make the
+typed reason invisible to consumers — the E-01 fix would be unreachable
+end-to-end through the primary client path. It changes to return a
+typed error carrying the `CallError` (a new
+`ChannelOpenError { error: CallError }` or equivalent), so the
+consumer branches on `channel:open_failed` + `details.reason`.
+
+This is a breaking change to a method signature introduced in this
+crate's 0.4.x — acceptable at 0.5.0 (see Consequences), and it is the
+point of the change: the reason must be consumer-usable.
+
+### 5. Compatibility and migration
+
+- `OpenHandler`'s type is unchanged. Existing registrations compile
+  unchanged.
+- `ChannelCore::register_openable` keeps its current signature
+  (no establisher = always-OK); a new
+  `register_openable_with_establisher(spec, establisher, open_handler,
+  registry, auth)` variant adds the hook. alkhttp's `OpenableAlpn`
+  gains an optional `establisher` field (default `None`) — the ferry
+  passes it through mechanically.
+- alktty migrates its **channels path** semantic failures (unknown
+  backend, `carriage != "raw"`, `allocate_failed`, ownership denial —
+  currently post-open error frames) into the establisher, resolving
+  them as `channel:open_failed`. Its direct-ALPN path **keeps** the
+  in-band error frame (two transports, two contracts; the direct path
+  has no open op to fail). The `0x00`-peek disambiguation stays for
+  the direct path only.
+- alkhttp is unaffected (no openable ops in the default surface; the
+  `OpenableAlpn` change is additive).
+
+### 6. Panicked pump handlers stay EOF-shaped (pinned as designed)
+
+The wrapper's teardown task swallows the pump handler's `JoinError`
+(`let _ = raw_task.await`). A panicked pump = instant EOF, which is
+the correct consumer-visible outcome for a mid-stream handler crash
+(indistinguishable from an abrupt close — there is no error channel
+mid-stream by design; establishment errors are the only kind that
+belong in the open reply). This ADR pins that as intended; no change.
+The establisher, by contrast, runs pre-reply — its panic (a future
+that panics when polled) surfaces as the spawned Once task's panic,
+which the serving loop already tolerates (the call never resolves;
+the deadline / client timeout is the bound). Establisher
+implementations return `EstablishmentError` instead of panicking, per
+this crate's no-panic convention.
+
+## Consequences
+
+**Positive:**
+
+- Establishment failure reaches the consumer as a typed, branchable
+  call error — retry policy, client UX, and error reporting become
+  possible for dial-refused, unknown-resource, and shortage cases
+  (previously: instant-EOF ambiguity).
+- The SSH contract ("the channel never exists opener-side") holds
+  consumer-visibly: a failed open never returns a `channel_id`.
+- No phantom channels: the ledger, policy count, and manager state are
+  restored atomically on failure — allocation and teardown balance.
+- alktty's per-crate in-band error vocabulary is retired on the
+  channels path; every future ALPN crate (alktunnels first) gets the
+  establishment reply for free.
+- ADR-047 §3's "channel plan" shape is realized: awaited preparation
+  before reply, spawned pumps after.
+
+**Negative:**
+
+- `channel:open_failed` + the reason vocabulary is a new wire-visible
+  error surface — additive, but it joins the stable error set
+  consumers may branch on (per ADR-016, `details` shapes are
+  discoverable via `services/schema`).
+- `ChannelClient::open_channel`'s error type changes (breaking at
+  0.5.0; mechanical for consumers — the `String` was a
+  debug-formatting wrapper anyway).
+- `OpenableAlpn` (alkhttp) gains a field; its two construction sites
+  add `None` (mechanical).
+- The establisher await adds a bounded latency to open-op replies
+  where handlers previously replied instantly (the spawn). The 10s
+  default is the worst case for a hung establisher; real establishers
+  (dial, lookup) complete in dial-time. Consumers already tolerate
+  call-op latency; the deadline is the bound.
+
+## Door type
+
+**One-way (wire-visible error surface).** `channel:open_failed` and its
+`details.reason` vocabulary join the stable error set: once consumers
+branch on reason codes, changing the vocabulary requires a migration
+(the same one-way-ness ADR-016 gives typed error details). The
+establisher hook shape itself — `OpenEstablisher`, the
+`register_openable_with_establisher` variant, the
+`Establishment`/`EstablishmentError` types — is a **two-way-door
+implementation detail** within the one-way decision (the wrapper shape,
+per ADR-047 §3's own door-type note). The `OpenHandler` type is
+untouched, which is what keeps the split cheap to revise.
+
+## Implementation units
+
+1. **alkcall 0.5.0** — `OpenEstablisher` +
+   `register_openable_with_establisher`; wrapper flow (await bounded →
+   teardown-on-failure → `channel:open_failed` with details);
+   `ChannelClient::open_channel` typed error (N-1); tests:
+   - establisher fails after allocation → consumer's `open_channel`
+     resolves `Err(channel:open_failed)` + reason details; channel
+     absent from `channel_ids()` afterward;
+   - establisher never completes → `timeout`-reason failure within the
+     deadline, channel torn down, ledger decremented;
+   - no-establisher registration behaves exactly as today (compat
+     gate);
+   - establisher success spawns pumps and replies `{channel_id}`
+     unchanged.
+2. **alktty migration** — channels-path semantic failures move into an
+   establisher; `open_via_channels_surfaces_negotiation_rejected`
+   resolves via call error; the direct-ALPN error-frame path is
+   retained.
+3. **alkhttp pass** — `OpenableAlpn.establisher: Option<...>` (default
+   `None`), threaded through the session fork (mechanical).
+
+## References
+
+- Review 006 E-01 (the establishment gap — findings and prior-art
+  survey), N-1 (the client error-type gap this ADR also resolves),
+  E-03/E-04 (adjacent teardown/early-arrival notes, filed separately
+  from this ADR's scope)
+- ADR-047 §3 (openable ALPNs are operations — the "channel plan"
+  wrapper shape this ADR restores; §7 opener ledger — the teardown
+  un-increment path)
+- ADR-016 (typed error schemas — the `details` vehicle)
+- ADR-040/041 (backpressure/caps — untouched; the teardown path keeps
+  the ledger `take` as the atomic gate)
+- alktty ADR-009 (the open op's input is the negotiation) + review 001
+  L1/L3 — the in-band mechanism retired on the channels path
+- alktunnels OQ-TN-09 (dial-failure reporting — the first consumer of
+  the new error) and `docs/research/ssh-socks5-survey.md`
+  §"Open-failure path" (the reason-code prior art)
+- RFC 4254 §5.1, RFC 1928 §6 — SSH/SOCKS5 open-failure semantics
+
+## Amendment (Unit 1 implementation, 2026-09-06)
+
+Unit 1 landed in alkcall 0.5.0. Two implementation-shape notes, both
+within this ADR's two-way door (the hook shape is the revisable
+implementation detail; the wire surface is unchanged from §1/§3):
+
+1. **The establisher does not receive the channel `Connection`.** §1's
+   signature sketch passed `Connection` to the establisher, but the
+   channel's `BiStream` is yield-once (`ChannelBidiStreamSource`) — it
+   cannot be handed to both the establisher and the pump handler, and
+   the establisher is pre-data-plane by design (its dial targets the
+   backend, not the channel). The implemented signature is
+   `Fn(Value, AuthContext) -> BoxFuture<'static,
+   Result<Establishment, EstablishmentError>>`; the `Connection`
+   belongs exclusively to the `OpenHandler` (unchanged).
+   **Identity semantics (CF-005 corollary, 2026-09-07):** the
+   `AuthContext` the establisher and the pump handler receive is the
+   **per-call** context — the opener's dispatch-resolved identity (the
+   same identity the ACL gate and the per-identity cap check saw)
+   overlaid onto the install-time context; transport-truthful fields
+   (`alpn`, `remote_addr`, `tls_client_fingerprint`) stay
+   install-time. On a per-connection registry (ADR-047 §4) this is
+   identical to the install-time context; on hub-forwarded opens the
+   establisher sees the end client, not the hub.
+2. **The bound is the earlier of the dispatch deadline and the
+   per-registration timeout.** §2 names the dispatch deadline "when
+   the `OperationContext` carries one, else the crate constant";
+   implemented as `min(deadline_remaining, timeout_override |
+   ESTABLISHMENT_TIMEOUT)` — the registration override stays
+   meaningful for `Query`/`Mutation`-typed open ops (whose dispatch
+   carries a 30s deadline; `Sub` clears it), and a deadline already in
+   the past yields a zero bound (immediate `timeout` reason).
+
+Implemented surface: `OpenEstablisher`, `Establishment`,
+`EstablishmentError` (reasons `dial_failed`/`unknown_resource`/
+`resource_shortage`/`handler_error` + the wrapper's `timeout`),
+`ESTABLISHMENT_TIMEOUT` (10s), `CHANNEL_OPEN_FAILED`
+(`channel:open_failed`), `ChannelCore::register_openable_with_establisher`
+(`register_openable` delegates with `establisher: None`),
+`ChannelOpenError` (client-side typed error: `CallFailed { error:
+CallError }` / `MissingChannelId` / `AdoptFailed`, with
+`call_error()` + `establishment_reason()` accessors). All four
+verification gates from the review landed as tests (establisher
+failure e2e through a real channels connection with ledger
+un-increment + no-channel assertions, bounded timeout, no-establisher
+compat, establisher-success pump round-trip).
+
+## Amendment 2 (plan payload, 2026-09-07 — review 007 R-01/R-02)
+
+Review 007 (from the alktunnels UDP POC) filed two follow-ups on the
+establishment surface; both landed in alkcall 0.6.0.
+
+**1. `Establishment` carries the channel plan (R-01).** §1 reserved
+the payload ("today: nothing") and the wrapper consulted only
+success/failure — so an establisher whose backend produces a handle
+(a dialed socket, a TTY allocation) had to cross it to the pump
+handler through a per-crate side channel. The alktunnels POC shipped
+a resource-keyed slot + poll loop whose concurrent same-resource race
+is unfixable within that shape; alktty documented the same wall
+(backend `allocate` cannot cross, so failure classes stayed in-band —
+the phantom-channel shape ADR-049 removed, alive one layer down).
+
+The plan is now real: `Establishment { plan: Option<ChannelPlan> }` with
+`ChannelPlan = Arc<dyn Any + Send + Sync>` — **typed-opaque, not
+`serde_json::Value`**. The review's `Option<Value>` sketch could not
+satisfy its own verification gate ("establisher dials, `plan` carries
+the handle"): the payloads establishers actually hand off are live
+handles with no JSON representation. The establisher and the
+`OpenHandler` agree on the concrete type; alkcall never inspects it.
+The wrapper threads `establishment.plan` to the handler's new second
+parameter (`OpenHandler = Fn(Value, Option<ChannelPlan>, Connection,
+AuthContext) -> JoinHandle<()>`); the separate-parameter shape wins
+over merging into `input` because a typed payload cannot ride the
+JSON input without a downcast-side registry and the reserved-key
+collision the review already anticipated. The plan is process-local
+(establisher → wrapper → handler on the producing side); the wire
+surface is unchanged — nothing crosses the transport that isn't
+already the open op's input. `#[non_exhaustive]` on `Establishment`
+keeps a future carrier change from being another breaking release.
+Construction is `Establishment::new(plan)` /
+`Establishment::default()`; the 0.5.0 `Ok(Establishment {})` sites
+break mechanically at 0.6.0, which is the point of landing this now
+(before alktunnels Phase 1 ships the side-channel shape into a real
+crate and the payload lands later anyway as a second break).
+
+**2. The `OpenHandler` lifetime contract is documented (R-02).** The
+wrapper awaits the returned `JoinHandle` and its completion triggers
+teardown — so the handle must track the data-plane lifetime: a
+handler that returns before its pumps finish tears the channel down
+at birth (the POC's first pump implementation hit exactly this: every
+tunnel connected then instantly EOF'd). The contract was implemented
+but never documented; the type docs now state it ("await the pumps
+inline, never spawn-and-forget and return early") on `OpenHandler`
+and the registration entry points, plus a `debug!` telemetry line in
+`run_open_wrapper` when a handler exits without having accepted the
+channel's `BiStream` (the birth-teardown hint; the accept is
+observable in-process via the yield-once source). §6's pinned
+EOF-shaped panic semantics are unchanged.
+
+## Amendment 3 (establisher reply projection, 2026-09-16 — review 008 U-2)
+
+Amendment 2 filled the establisher → handler direction (the plan);
+the establisher → opener direction stayed empty — the wrapper
+hardcodes the success reply to `channel_id`
+(`run_open_wrapper`'s `ResponseEnvelope::ok`). alktunnels ADR-008's
+bind-first listen establisher ends establishment at bind time, and the
+observed OS-chosen bound address must ride the open-op reply as an
+additive `"bound"` field (the SOCKS5 BIND reply#1 `BND.ADDR` fidelity
+ask) — the alternative (an out-of-band query op) is a new wire
+surface, strictly worse than an optional reply field.
+
+**The decision: `Establishment` gains optional reply fields the
+wrapper merges into the success output.**
+
+- The carrier: `Establishment.reply_fields: Option<Map<String,
+  Value>>` (private, builder-constructed) —
+  `Establishment::new(plan).with_reply_field("bound", json!({...}))`,
+  plus `with_reply_fields(map)` (batch) and `reply_fields()` (read).
+  The map shape generalizes beyond `bound` without a fourth
+  amendment; `#[non_exhaustive]` (amendment 2) made the carrier
+  extension additive — no construction-site break.
+- The merge: on establisher success the wrapper extends the success
+  output with the contributed fields AFTER reserving `channel_id`.
+  **The `channel_id` reservation:** the key is wrapper-owned; an
+  establisher supplying it is an establisher bug — the wrapper fails
+  the open loudly (`channel:open_failed`, reason `handler_error`,
+  message naming the reserved key) and tears the just-allocated
+  channel down, never silently shadowing its own value. Contributed
+  fields otherwise merge flat; the output schema remains the op's own
+  concern (the producing crate documents its optional fields —
+  alktunnels' listen-op spec documents `bound`).
+- The client read path: `ChannelClient::open_channel_with_reply`
+  returns `(channel_id, reply, send, recv)` — the full success
+  output — so a consumer reads `bound` without dropping to
+  `call_open_op` + manual `adopt_channel`;
+  `open_channel` delegates and discards the extra fields, signature
+  unchanged.
+- Compatibility: absent reply fields leave the reply byte-identical
+  to the pre-amendment shape (`{ channel_id }`) — verified by test.
+  Old consumers (`open_channel` extracting `channel_id`, ignoring
+  unknown fields) are unaffected by a NEW field; new consumers reading
+  `bound` against an OLD alkcall see the field absent — the additive
+  posture alktunnels ADR-008 §2 pins.
+
+Door type: the reply fields are an additive call-plane JSON surface
+(like `channel:open_failed`'s `details` in §3 — consumers ignore
+unknown fields by the envelope's own parse posture); the field set an
+op may contribute is the producing crate's schema concern, not a
+protocol vocabulary. No data-plane change.
+
+Implemented surface (alkcall 0.8.0): `Establishment::with_reply_field`
+/ `with_reply_fields` / `reply_fields`, the wrapper's
+reservation check (`RESERVED_REPLY_KEY` = `channel_id`) +
+`merge_reply_fields`, `ChannelClient::open_channel_with_reply`.
+Verification gates landed as tests: the projection produces
+`{ channel_id, bound }` on the wire; no-fields (establisher or not)
+produces exactly `{ channel_id }` (byte-identical); the reserved-key
+establisher fails with reason `handler_error`, channel torn down,
+ledger decremented, handler never spawned; the e2e gate carries
+`bound` through a real channels connection to
+`open_channel_with_reply` while `open_channel` stays unchanged.
@@ -0,0 +1,105 @@
+# ADR-050: `pump_bidi` — the two-pump helper, extracted upstream
+
+## Status
+
+Accepted — implemented in alkcall 0.6.0 (review 007 Unit 3 / R-03).
+Pins alknet ADR-078's two-pump contract in one place.
+
+## Context
+
+alknet ADR-078 defined the two-pump data-plane contract for forwarding
+channels (one pump per direction; each pump shuts the opposite sink
+down on completion — `try_join!` alone deadlocks) and deferred helper
+extraction until a second two-pump consumer existed and the shapes
+converged. Review 007 (R-03) supplied both halves of that test from
+the alktunnels UDP POC:
+
+- **Producer side:** the POC's `pump_halves` — two `tokio::io::copy`
+  pumps over split channel-vs-substrate halves, each shutting down
+  the opposite sink on completion, joined.
+- **Consumer side:** `TunnelSession::take_halves` + the assembly
+  layer's copy — the same shape modulo channel side.
+
+alktty's channels session already implements the shape (its
+`drive_session_pre_negotiated` awaited inline); alkhttp's ferry does
+not pump. The shapes converged; the review asked this sweep to either
+extract the helper or record the decision not to — an un-extracted
+helper would surface during alktunnels Phase 1 as the same
+fix→publish→update treadmill for a purely additive change.
+
+## Decision
+
+Extract the helper as `channels::pump_bidi`:
+
+```rust
+pub async fn pump_bidi<C, R, W>(channel: C, peer_read: R, mut peer_write: W) -> (u64, u64)
+where
+    C: AsyncRead + AsyncWrite + Unpin,
+    R: AsyncRead + Unpin,
+    W: AsyncWrite + Unpin,
+```
+
+Two pumps, joined: `channel → peer_write` and `peer_read → channel`.
+On each pump's completion the opposite sink is shut down
+(shutdown-on-completion — the half-close the contract specifies).
+Returns the two copy counts for observability.
+
+Three deliberate deviations from the review's sketch, all
+semantics-first:
+
+1. **Return `(u64, u64)`, not `io::Result<(u64, u64)>`.** There is no
+   meaningful `Err` state: both pumps swallow copy errors by contract
+   — a mid-stream error is indistinguishable from an abrupt close
+   (no error channel exists mid-stream, per ADR-049 §6's pinned
+   EOF-shaped semantics), and shutdown-of-the-opposite-sink runs
+   either way. A returned `Err` would be dead code; the counts
+   (with `unwrap_or(0)` on error) are the observability.
+2. **Peer side takes split halves (`peer_read: R`, `peer_write: W`),
+   not one `AsyncRead + AsyncWrite` value.** The dominant producer
+   shape is the establisher's dial result: `TcpStream::into_split`
+   halves (tunnels), pty pair halves (TTY). Taking halves matches the
+   POC (`pump_halves`) and avoids forcing consumers to re-join halves
+   just to satisfy a bound. The channel side stays a single value —
+   that is what the pump handler's `accept_bi` yields.
+3. **Not `async fn` over `AsyncWriteExt` bounds on both sides.** The
+   channel side needs `tokio::io::split` (one value, two pumps), so
+   its bound is `AsyncRead + AsyncWrite + Unpin`; the `AsyncWriteExt`
+   bound the sketch had on every parameter is the extension trait
+   only where shutdown is called.
+
+alktty's three-pump session does not fit the helper (the exit future
+is a third signal) and stays as-is — the helper serves the two-pump
+shape, exactly as the review scoped.
+
+## Compatibility
+
+Purely additive: a new pub fn in `channels::pump`, re-exported in the
+module docs; no existing surface changes. Consumers may adopt it at
+their own pace (alktunnels Phase 1 gets it for free; alktty's
+channels session can migrate later if it wants; the POC's shape is
+now canonical).
+
+## Door type
+
+**Two-way.** A helper function is trivially removable or re-shapable;
+no wire surface, no trait, no state.
+
+## Verification gate
+
+The POC's two-pump semantics reproduced through the helper, as unit
+tests in `src/channels/pump.rs`: data flows both directions with
+exact copy counts; EOF from one side completes the other's
+shutdown-on-completion (the far end observes clean EOF, not an
+error); a dead source is EOF-shaped teardown, not an `Err`.
+
+## References
+
+- Review 007 R-03 (the extraction ask + the convergence evidence)
+- alknet ADR-078 (the two-pump contract; shutdown-on-completion)
+- alktunnels `poc-summary.md` §Issues Surfaced #4 (the producer-side
+  shape; `pump_halves` in the POC's producer.rs)
+- alktty `src/channels.rs` (the channels session shape; three-pump
+  carve-out)
+- ADR-049 amendment 2 (R-02 — the lifetime contract the helper's
+  callers must respect: await `pump_bidi(..).await` inline inside the
+  handler task)
@@ -0,0 +1,343 @@
+# ADR-051: In-Tree Channel Relay (`ChannelRelay`) and the Hub-Leg Assembly
+
+## Status
+
+Accepted (2026-09-17) — amends ADR-042 (the relay contract's
+implementation home moves into alkcall; the translate-not-forward
+contract is unchanged). Sequenced after review 008 remediation Units 1
+and 2 (both landed, alkcall 0.8.0): the relay's establisher projects
+the spoke reply's extra fields via `Establishment` reply fields
+(ADR-049 amendment 3), and the spoke's flavor-form open ops arrive
+reconstructed WITH the `channel_open` marker through discovery
+(ADR-047 amendment 3). All three implementation units are landed:
+Unit 3a (the `ChannelRelay` component, §1–§4, §6) in
+`src/channels/relay.rs`, Unit 3b (the hub-leg install template, §5) in
+`src/channels/hub_leg.rs`, and Unit 3c (the review's gate-2 e2e
+harness, gates 6/7) in `src/channels/gate2_tests.rs` — alkcall 0.8.0.
+
+## Context
+
+Review 008's remediation plan (Unit 3) pinned the in-tree relay as the
+implementation of the review's U-1 gate 2 — the hub-relay round trip
+that proves flavor-form marked ops survive discovery into a genuine
+relay. The as-filed ADR-042 §"Scope note" put the relay implementation
+in `alknet-hub`/downstream; the consumers that now exist (alktunnels'
+graduation, alkhttp's fallback hub, alknodes, and the hub/spoke family
+behind them) all need the same shape, so the implementation moves into
+alkcall as a reusable export.
+
+The consumer family the relay must serve is the hub/spoke composition:
+spokes connect to a hub and expose services; the hub re-exposes those
+services to other spokes (and consumers) based on ACL. Both a hub and
+a spoke can be a relay depending on the setup. A canonical example:
+spoke A exposes `channels/tunnel/direct`; the hub imports it via
+`from_call`, gates it with its own ACL, and re-exposes it on its
+consumer-leg channel-0 registries; spoke B opens through the hub and
+the hub relays the channel to spoke A. The hub performs no port
+binding and no protocol work on the data plane — the property that
+makes the hub-acl-relay role cheap (alktunnels' no-bind posture, the
+same property ADR-042 §What the hub runs pins: "the hub never runs a
+handler for `alk/tty`, `alk/ssh`, or `alk/tunnel`").
+
+Two implementation surfaces were evaluated for the data plane; the
+decision records why the wrapper-composition shape wins over
+byte-forward-with-rewrite.
+
+## Decision
+
+### 1. The relay is the wrapper composition — translate-not-forward, implemented with the existing open-op machinery
+
+ADR-042's two-layer contract is implemented as composition of pieces
+this crate already has:
+
+- **Layer 1 (call-protocol translate)** is the ADR-049 establisher:
+  the hub's consumer-leg open op resolves through the full open-op
+  wrapper (registry ACL → per-identity cap → allocation), then the
+  establisher calls the producer leg's open op, adopts the returned
+  spoke channel id into the producer-leg `ChannelManager`, and returns
+  `Establishment::new(plan)` whose plan carries the spoke-leg streams.
+  The hub allocates its own consumer-leg `channel_id`; the spoke
+  allocated its own producer-leg id; the two ids never appear in each
+  other's namespaces.
+- **Layer 2 (byte-forward)** is the ADR-050 `OpenHandler`:
+  `pump_bidi(consumer_leg_bistream, spoke_recv, spoke_send)` — the
+  pump's generic bounds already match the relay's two legs. The relay
+  never parses chunk framing on either leg; the mux/demux on each leg
+  absorbs the 8-byte header (ADR-034) and the channel-id namespaces
+  are per-connection, so no header rewrite exists. Awaited inline per
+  the R-02 lifetime contract; on completion both legs tear down (the
+  wrapper's handler-exit teardown covers the consumer leg; the pump's
+  send/recv drops EOF the spoke leg).
+
+**The relay map dissolves.** ADR-042 §`channel_id` mapping pinned a
+`HashMap<channel_id, channel_id>` per (browser, spoke) pair maintained
+by the hub. The implementation needs no map: each leg's `ChannelManager`
+already holds its own id → routing state, and the per-channel pump
+closure binds both legs' streams. The mapping is implicit-per-channel.
+This is a two-way-door implementation detail within ADR-042's contract
+(the ADR itself marked the mapping strategy two-way).
+
+**`channel/close` and `channel/control` need no translation surface.**
+Consumer-side close → wrapper teardown → pump abort → send-half drop →
+EOF chunk → spoke handler exits → spoke's own wrapper decrements its
+ledger. Close propagates through the EOF cascade with correct ledger
+accounting on both legs; the hub never sees a `channel/close` to
+translate. Control stays per-leg (`channel/control` is not implemented
+upstream, OQ-39 — a hub wanting cross-leg control translation composes
+it downstream). This supersedes the ADR-042 §mapping bullet's
+close-translation sentence as an implementation matter: the mapping
+entry the sentence's removal depended on does not exist.
+
+### 2. What the relay holds on the producer leg: `CallConnection` + `ChannelManager`
+
+The relay's producer-leg surface is `Arc<CallConnection>` (for the
+translate hop's open call) plus the producer-leg `ChannelManager` (for
+`adopt_channel` and teardown visibility) — not a `ChannelClient`.
+
+Rationale: `ChannelClient`'s calling surface detaches on
+`take_call_connection` (the hub needs the connection for `from_call`
+import AND for the relay's establisher AND possibly its own ops —
+three claimants), while `Arc<CallConnection>` is `Clone` and the
+client's manager accessor yields the same `ChannelManager` the relay
+needs. A hub that dials the spoke with `ChannelClient::from_connection`
+and then tears the client down after import keeps the relay alive on
+the `Arc`s. The establisher builds its forwarded payload directly
+(`build_forwarded_payload` semantics — the hub as caller, the consumer
+as `forwarded_for`, ADR-026 §3) rather than through
+`call_open_op`, which carries no payload variant.
+
+The spoke reply's `channel_id` is stripped before projection (the
+consumer-leg reply carries the hub-allocated id, not the spoke's);
+the spoke reply's other fields ride through `with_reply_fields` —
+`bound` flows end-to-end with per-hop truthfulness (a hub re-producing
+a listen resource binds its own listener and contributes its own
+`bound`; alktunnels ADR-008 §Hub re-produce).
+
+### 3. Reason-code mapping (spoke `CallError` → `EstablishmentError`)
+
+The spoke's open can fail with the full call-error vocabulary; the
+establisher maps it into `EstablishmentError` by class:
+
+| Spoke failure | `EstablishmentError` variant | Wire reason |
+|---|---|---|
+| `channel:open_failed` with a typed reason | the same class — `DialFailed` for `dial_failed`/`timeout`, `UnknownResource` for `unknown_resource`, `ResourceShortage` for `resource_shortage`, `HandlerError` for `handler_error` | the mapped reason |
+| `channel:open_failed` reason `timeout` | `DialFailed` (the spoke establishment exceeded the spoke bound — from the consumer's side it is unreachable-target-shaped) | `dial_failed`, spoke message preserved |
+| `NOT_FOUND` (spoke predates the op) | `HandlerError` carrying the code | `handler_error` |
+| `FORBIDDEN` (hub lacks the spoke grant) | `HandlerError` carrying the code | `handler_error` |
+| other `CallError` | `HandlerError` carrying the code | `handler_error` |
+
+The spoke's original code and message are preserved in the mapped
+variant's `message` (never discarded — a consumer debugging a
+FORBIDDEN-through-relay must see the spoke's grant failure, not a bare
+`handler_error`). The `timeout` mapping is the one non-1:1 case: the
+consumer-visible reason is `dial_failed` because establishment
+timeouts are wrapper-generated (ADR-049 §3) and not an establisher
+vocabulary word; the spoke's message carries the truth.
+
+### 4. The registration seam: two phases, fork-registry registration
+
+Openable ops register on a **per-connection fork of the hub's base
+registry** installed as the consumer leg's dispatch registry (the
+ADR-047 §4 amendment mechanism). Discovery of the producer leg's ops
+happens once (hub startup or reconnect); registration happens per
+consumer-leg connection inside the `install_channel_zero` hook. The
+one-call signature the review sketched cannot exist without adapter
+changes — the two phases are the API:
+
+1. **Discover/stash** — `from_call` against the producer leg returns
+   the imported `HandlerRegistration` bundles. Marked specs (rebuilt
+   WITH the `channel_open` marker, ADR-047 amendment 3) are separated
+   from plain bundles by the marker. The stash is a `Clone`able
+   template: `HandlerRegistration` and `HandlerKind` are `Clone`, and
+   `OperationRegistry::fork` deep-copies registrations, so one
+   discovered set serves any number of consumer legs.
+2. **Register per connection** — the hub-leg install hook forks the
+   base registry, registers the generic channel ops
+   (`ChannelOperations::register_on`), registers the stashed plain
+   bundles as-is (the existing forwarding handlers), and registers
+   each stashed marked spec via the relay's
+   `register_relay_openable` (the fork is the `consumer_registry`
+   argument), then dispatches channel 0 over the fork.
+
+Per-consumer ACL differentiation is a composition consequence, not a
+mechanism: the fork is per consumer leg, so a hub re-exposing
+different op subsets to different consumers filters the stash per
+fork. The imported spec's own `access_control` remains the gate for
+the re-exposed op; the hub composes additional ACL at its assembly
+layer.
+
+### 5. The hub-leg install hook is an in-tree export (the call-half support)
+
+Every existing test hand-rolls the hub-side install hook
+(`make_install_channel_zero`-shaped); the hub/spoke family all need
+the same composition. The relay lands with a documented hub-leg
+template — fork, generic ops, bootstrap discovery, stashed bundles
+(plain + relay), per-call identity resolution (`ServingConfig`-shaped),
+single-stream dispatch loop — as an in-tree composition (unit-scoped:
+Unit 3b). This is composition of existing pieces, not a new protocol
+surface; its exact API shape is a two-way-door implementation detail.
+The spoke side needs nothing new: a spoke serving ops through a hub is
+the existing connect-side serving shape (`from_connection_with_serving`)
+plus the producer-leg registration it already does.
+
+**ACL layering note (pinned, because it surprises):** the spoke's
+`AccessControl` sees only the hub's identity — the end consumer's
+identity rides `forwarded_for` as metadata and is never consulted by
+any `AccessControl::check` (ADR-024/ADR-026). "The hub re-exposes
+based on ACL" therefore means: the hub-side gate is the imported
+spec's ACL (+ hub policy) on the consumer leg; the spoke-side grant
+goes to the hub identity, which needs scopes on every spoke op it
+relays. The end consumer never authenticates to the spoke directly.
+
+**Loud-install coverage note (review 009 C-1):** the template's four
+install-failure arms all end the install task before the dispatch
+loop (channel 0 never dispatches — never a silent stub). Two arms are
+unit-test-pinned: the relay-openable registration failure (the
+Pub-typed marked spec gate) and the plain-bundle registration failure
+(an un-compilable schema — the registry's fail-closed rule). The
+other two arms — generic channel-ops registration and bootstrap
+discovery install — are best-effort-loud: both register
+crate-internal specs whose schemas compile by construction, so
+failure is not reachable through any public path and an injectable
+failure seam would test the seam, not the arm. This note is the
+contract: if a future change makes either arm reachable, it gets the
+same pin.
+
+### 6. Bounds: rejected shapes and residual notes
+
+- **Pub-typed open ops** — rejected loudly (`channel:pub_open_not_implemented`,
+  the C-08 blocker). The relay registers only `Query`/`Mutation`-typed
+  ops (plain forwarding) and `Sub`-typed marked ops (relay openables);
+  a discovered `Pub`-typed marked spec is an assembly error, not a
+  silent stub.
+- **Compounding establishment bounds** — each hop's establisher is
+  bounded independently (ADR-049 §2); an N-hop chain adds N bounds.
+  The consumer's dispatch deadline (`min(deadline, 10s)` per hop)
+  bounds each hop, not the chain. No fix — noted for capacity
+  planning.
+- **Mid-establishment consumer disconnect** — the one teardown window
+  with a delay, with two reclaim signals pinned by the Unit 3c gate
+  (`gate2_mid_establishment_disconnect_reclaims_without_leak`): (a)
+  the consumer leg's just-allocated channel reclaims at the leg's own
+  transport EOF (`clear_all` + ledger decrement) — the hub has not
+  adopted, so the producer leg stays clean; (b) the spoke's channel —
+  the spoke allocates before its establisher replies — is the honest
+  residual: it cannot be reclaimed by the hub (no adoption exists),
+  so it lingers until a spoke-side teardown signal (the spoke↔hub leg
+  ending, or the spoke's own establishment bound). The gate bounds
+  the window deterministically by severing the spoke leg and asserts
+  the spoke-side reclaim + ledger decrement. A channel never outlives
+  its leg lifetimes; never a leak past the connection's lifetime.
+- **Adopted-entry teardown on every plan path** — the hub's
+  producer-leg entry (the `adopt_channel` state) is owned by the
+  relay's `RelayPlan` via a `Drop` guard, so it reclaims whenever the
+  plan dies: the normal pump completion, the pump handler's
+  early-return arms (plan absent, downcast failure, `try_unwrap`
+  failure, `accept_bi` failure), and the wrapper's establishment
+  bound expiring after the adopt (the plan dropped before the pump
+  ever spawns). Dropping the plan's send half also EOFs the spoke
+  side through the mux pump's implicit-EOF sentinel (REQ-CH-01), so
+  the spoke handler reclaims through the same cascade the normal
+  path   uses. This closes the adopt-then-timeout window the landing
+  review surfaced (the §6 window above is the *pre-adopt* window;
+  this is the *post-adopt* one, now closed by construction). The
+  one remaining cancellation point *inside* `adopt_channel`'s own
+  await is the same pre-existing client-side window
+  (`ChannelClient::open_channel`'s adopt has it too) — bounded by
+  the leg's transport-EOF `clear_all`, not by the plan.
+- **Multi-hop relays** — a chain of relays composes (each hop is a
+  hub leg pair), with the compounding-bound note above. No special
+  machinery.
+
+## Consequences
+
+**Positive:**
+
+- The relay is O(1) new machinery: an establisher closure, a
+  `pump_bidi` handler, and a registration entry point. No parallel
+  auth path (the consumer leg's full wrapper machinery applies), no
+  new wire surface (the relay speaks only already-stable ops), no
+  data-plane parsing (ADR-034's one-way door stays closed).
+- `from_call` gains a real in-tree consumer for the marker-branching
+  seam Gap C named (ADR-047 §Gap C): downstream crates compose
+  `ChannelRelay` instead of re-deriving the hub shape.
+- U-1's gate 2 (the review's silent-failure scenario — flavor-form ops
+  relaying as plain forwarding stubs) becomes a permanent e2e gate.
+
+**Negative:**
+
+- New pub API (`ChannelRelay`, the registration entry point, the
+  hub-leg template) — minor bump, one release with the review's other
+  units, review-007 precedent.
+- The two-phase discover/stash-then-register shape is more assembly
+  code for a trivial hub than a one-call import would be. The fork
+  mechanism forces it; the stash being `Clone` keeps the per-connection
+  work cheap.
+- The hub holds `Arc<CallConnection>` + `ChannelManager` per spoke leg
+  for the connection's lifetime — per-leg state, bounded by the spoke
+  count.
+
+## Door type
+
+**Two-way (implementation shape) within a one-way posture.** The
+translate-not-forward contract (ADR-042) and the ACL layering are
+unchanged one-way decisions; the in-tree export, the implicit-mapping
+implementation, and the two-phase registration shape are revisable
+implementation details — downstream crates compose the export, not the
+internals. The rejection posture for Pub-typed marked ops is loud (an
+assembly error), so a future implementation of the Pub path is
+additive.
+
+## Verification gates (implementation units)
+
+Unit 3a (the relay component):
+
+1. `register_relay_openable` on a forked consumer-leg registry
+   resolves the open op end-to-end; the establisher populates
+   `forwarded_for` from the consumer's per-call identity (ADR-026 §3)
+   and strips the spoke reply's `channel_id`.
+2. A spoke `channel:open_failed` maps to the consumer-leg
+   `channel:open_failed` with the mapped reason (the §3 table) and the
+   spoke's message preserved; the consumer leg tears down (ledger
+   decremented); no spoke channel leaks.
+3. `bound` (Unit 1's reply projection) survives the relay to the
+   consumer reply.
+4. Pub-typed marked specs are rejected at registration.
+
+Unit 3b (the hub-leg template):
+
+5. The template composes fork + generic ops + bootstrap discovery +
+   plain bundles + relay openables + serving identity and dispatches
+   channel 0; `services/list` on the consumer leg shows the
+   re-exposed ops.
+
+Unit 3c (the gate-2 e2e):
+
+6. The review's full harness: consumer → hub (forked channel-0
+   registry + relay) → producer, opening `channels/tunnel/direct` end
+   to end: the open resolves with the hub-allocated `channel_id`, the
+   establisher-contributed `bound` field survives to the consumer
+   reply, data flows both directions (the hub never parses it), and
+   hub-side disconnect / spoke-side close tears down both legs
+   (including the mid-establishment window from §6).
+7. A companion `channels/tty/sub` relay run pins no regression on
+   standard shapes.
+
+## References
+
+- ADR-042 (amended by this ADR — the implementation home; the
+  contract unchanged; the relay map and close-translation bullets
+  superseded by the implicit-per-channel shape)
+- ADR-047 amendment 3 (flavor-form ops reconstruct WITH the marker —
+  the discovery input this relay consumes), §Gap C (the
+  marker-branching seam), §4 amendment (the fork mechanism Unit 3b
+  composes)
+- ADR-049 amendments 2/3 (the plan payload the relay's establisher
+  carries; the reply projection `bound` rides through)
+- ADR-026 §3 (forwarded_for on the translate hop), ADR-050
+  (`pump_bidi` — the byte-forward hop), ADR-040/041 (the caps the
+  consumer leg keeps enforcing)
+- alktunnels ADR-007/008 (the first consumers: the direct op's relay
+  and the listen `bound` field's per-hop truthfulness)
+- Review 008 remediation plan Units 1–3 (the sequencing this ADR
+  lands inside)
@@ -83,7 +83,7 @@ is the load-bearing piece the broker composes on.
 | OQ-37 | `from_call` relay wrapper for marked ops | open | medium | ADR-047 §1 names it as a consumer (hub) concern; alkcall's `from_call` reconstructs the marker (Gap F resolved) so the consumer can branch on it |
 | OQ-38 | ALPN→path-segment mapping | resolved | low | ADR-047 §"Negative" — strip the `alk/` prefix; ALPNs without that prefix use the full ALPN string (rare, two-way-door) |
 | OQ-39 | `channel/control` control-handle surface | open | medium | The `channel/control` handler currently returns `channel:control_not_implemented`. The control-handle surface (per-channel control callbacks registered by ALPN crates, routing `message` to the handler's control handle for `channel_id`) is real design work — each ALPN crate needs a way to register a control callback, and the channels layer needs a control-handle registry keyed by `channel_id`. Deferred until an ALPN crate (TTY, tunnel) needs out-of-band control. |
-| OQ-40 | `channel/resources/subscribe` live subscription | open | medium | The `channel/resources/subscribe` handler currently returns `channel:resources_not_implemented`. The live subscription aggregated from ALPN-crate resource enumerators (ADR-047 §6) requires each ALPN crate to provide a resource enumerator, and the channels layer to aggregate them into a live `Stream` that emits on any change. The current stub is a one-shot error; the real implementation is deferred until a consumer (hub, dashboard) needs live resource discovery. |
+| OQ-40 | `channel/resources/subscribe` live subscription | open | medium | The `channel/resources/subscribe` handler currently returns `channel:resources_not_implemented`. The live subscription aggregated from ALPN-crate resource enumerators (ADR-047 §6) requires each ALPN crate to provide a resource enumerator, and the channels layer to aggregate them into a live `Stream` that emits on any change. The current stub is a one-shot error; the real implementation is deferred until a consumer (hub, dashboard) needs live resource discovery. **Load-bearing for alktunnels' discovery UI** (review 006 E-02): a consumer cannot distinguish produced tunnel resources by op name alone. The static half is covered (0.5.0: `OperationSpec.description` on `services/list` — describes the op, not the live resource set); the dynamic half stays deferred — alktunnels v1 uses config-known op names. |
 | OQ-41 | QUIC-native multi-stream substrate | open | medium | Only the in-line substrate mode is implemented (single bidi stream, header-demuxed N channels). The QUIC-native multi-stream substrate (accept remaining bidi streams, read headers off each — ADR-034 §substrate modes) is deferred to the downstream alknet crate. The wire format and demux loop are correct for both substrates; only the outer `accept_bi()` loop is missing. The alknet crate owns the QUIC dial/accept loop and is the natural place for the multi-stream accept loop. This crate stays transport-agnostic (no QUIC dependency, WASM-compatible). |

 ## Core Types
@@ -39,6 +39,9 @@ pub struct OperationSpec {
    pub output_schema: Value,     // JSON Schema for output
    pub error_schemas: Vec<ErrorDefinition>,  // Declared domain errors (ADR-016)
    pub access_control: AccessControl,
+    /// Human-readable op description (review 006 E-02). Disclosed by
+    /// `services/list` when set; `None` when the op declares none.
+    pub description: Option<String>,
    /// JSON pointer into the input for the resource ID, when
    /// `access_control.resource_type` is set and the operation targets a
    /// specific runtime-spawned resource (ADR-011). e.g., `"$.containerId"`
@@ -829,6 +832,12 @@ These are read-only — no admin operations are exposed through the call protoco
 }
 ```

+Each listing entry also carries `description` (review 006 E-02) when
+the op's spec declares one (`OperationSpec.description`, set via
+`with_description`) — the field is additive and absent otherwise. It
+describes the op, not the produced resource set: live resource
+discovery stays with `channel/resources/subscribe` (ADR-047 §6, OQ-40).
+
 `services/schema` accepts `{ "name": "fs/readFile" }` (no leading slash —
 registry form, same as `OperationSpec.name`) and returns the full
 `OperationSpec` including input/output JSON Schemas and declared
@@ -0,0 +1,814 @@
+# Fuzzing alkcall: Research and Recommendation
+
+**Status:** steps 1–3 of §7.4 adopted — `fuzz/` workspace, five targets,
+committed seeds, detached runner, two-tier campaigns run; one real
+finding (duplicate adopt/open destroying the live channel) fixed with
+regression tests. §7.2/§7.4's CI tiers are **not planned** — this repo
+will not run hosted CI (the git host is a minimal gitea that serves git
+only; see §7.9). CI's two deliverables are covered instead: the stable
+side's corpus replay (`cargo test --manifest-path fuzz/shared/Cargo.toml`)
+runs as part of every release's verification checklist (AGENTS.md), and
+campaigns run manually via the detached runner (§7.6)
+**Date:** 2026-09-27
+**Research inputs:** web survey of the 2025–2026 Rust fuzzing ecosystem, survey
+of fuzzing practice in comparable Rust protocol crates (rustls, quinn, quiche,
+h2, prost, s2n-quic, yamux/libp2p, serde_json), and a first-hand inventory of
+alkcall's untrusted-input parse surfaces (§5, verified against the code in
+this repo).
+
+---
+
+## 1. Should this crate be fuzzed?
+
+**Yes.** Three independent lines of argument converge:
+
+1. **Position in the dependency graph.** alkcall is the substrate crate:
+   vendored core types, the call protocol, and the channels demux/mux all
+   live here, and downstream crates consume the wire formats rather than
+   re-implementing them (ADR-031 crate decomposition, ADR-007/008/009
+   vendored types). A parser bug here propagates everywhere; a fuzzed
+   parser here protects the whole stack. Fuzzing "at this level and working
+   down" is the right order — it is exactly what rustls did (fuzz the
+   deframer at the bottom, then the state machines).
+
+2. **Wire formats are stable and attacker-reachable by design.** The
+   `EventEnvelope` framing (`{ type, id, payload: serde_json::Value }`
+   behind a 4-byte BE length prefix, ADR-014) and the channels 8-byte chunk
+   header (`[channel_id:u32 BE][len:u32 BE][payload]`, ADR-034) are
+   one-way doors. Both are parsed from bytes produced by *arbitrary peers*
+   — including relayed peers in the ADR-042 hub topology, where the hub
+   forwards bytes it never validated. The `payload` field is deliberately
+   schema-free JSON, so serde is on the attacker-controlled path with no
+   type-level defense.
+
+3. **The failure classes that dominate real-world findings in Rust are
+   present in this codebase's shape, and several already have concrete
+   candidate findings.** The rust-fuzz trophy case (250+ entries) shows
+   that for Rust protocol crates the dominant bug classes are not memory
+   unsafety but: panics on untrusted input, integer/length arithmetic
+   errors, OOM via length-prefix-driven allocation, and unbounded state
+   growth. alkcall is safe Rust end-to-end (zero `unsafe` blocks —
+   verified), which means **no memory-corruption class at all**, but every
+   other class maps directly onto code in `src/` (see §5 and §6.2).
+
+The strongest single datapoint: **RUSTSEC-2026-0037 / CVE-2026-31812
+(quinn-proto, March 2026, CVSS 8.7)** — a remote DoS via `unwrap()` in
+transport-parameter parsing. The maintainers' post-incident statement was
+explicit: *"we did not have sufficient fuzzing coverage to find this issue.
+We have since added a fuzzing target to cover this code path."* quinn-proto
+is structurally very close to alkcall (async Rust RPC-ish protocol crate,
+safe Rust, peers on the wire). A panic on attacker wire bytes in this crate
+would be the same CVE class — and "the code is well tested" did not save
+quinn, because conventional tests do not randomly explore malformed inputs.
+
+**The honest caveat (why this was not obviously required before):** alkcall
+has no `unsafe`, uses serde_json (whose 128-depth recursion limit and
+non-panicking parser absorb most JSON pathology), bounds both length
+prefixes before allocating (64 MiB frame cap, 16 MiB chunk cap — both
+verified), and has solid round-trip unit tests. So the *expected* yield is
+not memory-safety bugs; it is (a) panic-class bugs in hand-rolled dispatch
+parsing, (b) the DoS-class findings in §6.2 which no amount of
+example-based testing would have caught, and (c) regression protection for
+two stable wire formats. If the campaign's first months find nothing, that
+is a successful negative result, not a wasted one — it converts "we think
+the parsers are robust" into a demonstrated property.
+
+---
+
+## 2. Tool landscape (2025–2026 snapshot)
+
+| Tool | Version (date) | Engine | Toolchain | Status / verdict for alkcall |
+|---|---|---|---|---|
+| `cargo-fuzz` | 0.13.2 (2026-06) | libFuzzer | nightly required | **Recommended primary.** Actively maintained (rust-fuzz org), 3 releases since mid-2025, the de-facto standard; every surveyed protocol crate uses it. |
+| `libfuzzer-sys` | 0.4.13 (2026-06) | libFuzzer runtime | via cargo-fuzz | Re-exports `arbitrary`; `fuzz_target!` accepts any `Arbitrary` type. |
+| `arbitrary` | 1.4.2 (2025-08) | bytes → structured values | stable | **Recommended for structured targets.** `#[derive(Arbitrary)]`; 1.4.x brought notable fuzzing-speed wins. |
+| `afl` (afl.rs, wraps AFL++) | 0.18.2 (2026-05) | AFL++ | **stable OK** | Recommended secondary/optional engine — long campaigns, multi-core, no nightly needed. CMPLOG on by default. |
+| `honggfuzz` | 0.5.62 (2026-08) | honggfuzz | stable OK | Usable but upstream quiet since mid-2024; no reason to prefer over the above. |
+| `bolero` | 0.13.4 (2025-07) | front-end: libfuzzer/AFL/honggfuzz/**Kani**/plain `cargo test` | stable for test/random | Attractive "same test, both engines" model, production-proven at s2n-quic. Considered and **deferred** (§7). |
+| `libafl` | 0.16.1 (2025-08) | library for building fuzzers | stable | State of the art but a framework, not a tool; overkill for byte-buffer parser targets. Revisit only for stateful connection fuzzing. |
+| OSS-Fuzz | — | hosted service | nightly (provided) | Free continuous fuzzing; expects exactly the cargo-fuzz layout (`libfuzzer` + `address` only). Adopt after targets stabilize. |
+| `proptest` / quickcheck | mature | random generation + shrinking | stable | Complement, not replacement: no coverage guidance. Good for round-trip properties in the normal suite. |
+
+Corroborating detail on cargo-fuzz status: published on crates.io, install
+via `cargo install cargo-fuzz`; subcommands `init`, `add`, `run`, `fmt`,
+`tmin`, `cmin`, `coverage`; recent releases added `--fuzz-engine`,
+`--disable-branch-folding`, codegen-units tuning, Windows/MSVC support.
+libFuzzer itself is upstream-maintenance-mode (its authors moved to
+Centipede), which is irrelevant in practice for Rust app crates —
+cargo-fuzz remains the recommended path in the Rust Fuzz Book.
+
+---
+
+## 3. What comparable crates actually do
+
+Full details in the research notes; the load-bearing patterns:
+
+- **rustls** (the reference model): `fuzz/` workspace, 8 targets spanning
+  byte-parsers *and* full state machines; internals exposed to targets via
+  `#[cfg(fuzzing)] pub mod fuzzing` (targets get access without widening
+  the public API); invariants include consumption accounting
+  (`assert!(processed <= buf.len())`) and re-encode round-trips; fuzz
+  functions additionally exercised from plain unit tests; corpora in a
+  dedicated repo; CI runs **10 s per target on every push** + OSS-Fuzz
+  CIFuzz at 150 s on PRs.
+- **quinn**: `#[derive(Arbitrary)]` structured inputs; the `packet.rs`
+  target asserts the decoder consumed exactly the input
+  (`assert_eq!(len, decoded.0.len() + rest)`); a stateful target replays
+  `Vec<Op>` op sequences against `StreamsState`. Post-CVE, this is the
+  closest structural analogue to alkcall.
+- **quiche**: fuzzes the *whole* protocol handler with committed test
+  certs; 1800+ committed seed corpus files generated by a seed script; Mayhem for continuous fuzzing.
+- **h2**: the standout e2e pattern — fuzz input interpreted as a *script*
+  for mock I/O (length-prefixed chunks drive every socket read/write), so
+  libFuzzer explores partial-write/partial-read interleavings through the
+  full tokio state machine.
+- **prost**: libFuzzer + AFL side by side; decode-then-re-encode round-trip
+  invariant; committed seed corpus for the AFL side.
+- **yamux / libp2p** (no fuzz targets — the cautionary example): rely on
+  quickcheck only; their hand-rolled length-prefix handling shows the
+  defensive patterns fuzzing would police — `MAX_FRAME_BODY_LEN` checked
+  **before** `vec![0; body_len]` (yamux `frame/io.rs`), "validate RPC
+  limits by parsing the wire format without allocating" (libp2p gossipsub
+  `validate_rpc_limits`).
+- **s2n-quic**: bolero's flagship consumer — fuzz checks live as ordinary
+  `#[cfg(test)]` functions, run in normal CI as `cargo test` (corpus
+  committed as tarball per test), long-run under libFuzzer out-of-band,
+  and the same properties carry Kani proof attributes.
+
+**Invariant taxonomy observed across all repos** (in ascending strength):
+
+1. **No-panic** — baseline; `drop(result)` suffices because libFuzzer +
+   ASan + debug assertions catch panics.
+2. **Consumption accounting** — decoder consumed exactly the expected
+   bytes; nothing lost or duplicated (quinn packet, rustls deframer).
+3. **Round-trip** — `decode(encode(x)) == x` or `encode(decode(bytes))`
+   prefix-match (yamux, quiche qpack, s2n-quic, prost).
+4. **Resource bounds** — attacker-controlled lengths rejected (or skipped
+   without allocating) before allocation; bounded map growth.
+5. **Stateful op sequences** — structured `Vec<Op>` replay against
+   internal state machines (quinn streams, h2 MockIo).
+
+CI is universal but budgeted: the norm is a short per-push smoke run
+(10–300 s) plus a longer scheduled campaign; crash artifacts uploaded via
+`actions/upload-artifact` on failure. Cargo corpora are committed by
+quiche/rustls/s2n-quic, gitignored by quinn/h2.
+
+---
+
+## 4. Toolchain decision: cargo-fuzz + arbitrary, AFL optional, bolero deferred
+
+**Primary: `cargo-fuzz` + `arbitrary`.** Rationale: it is what every
+surveyed crate uses, so patterns and CI templates transfer directly; the
+`fuzz_target!` macro accepts both raw `&[u8]` and `Arbitrary`-derived
+types, which maps onto alkcall's two input shapes (malformed-byte hunting
+vs. structured logic replay); OSS-Fuzz compatibility for free; nightly
+requirement is confined to the fuzz job (a pinned nightly toolchain for
+the `fuzz/` workspace only — the crate itself stays stable at MSRV 1.88
+and the fuzz crate is excluded from publishing via `exclude` in
+`Cargo.toml`).
+
+**Secondary (optional, later): `afl` (AFL++).** Stable-toolchain, good for
+long multi-core campaigns and as an independent engine to cross-check
+findings (prost runs exactly this pairing). Not needed for the initial
+rollout.
+
+**Deferred: bolero.** The s2n-quic model (fuzz check colocated as a normal
+unit test, replayed in CI with a committed corpus, long-run out-of-band)
+has a real advantage for this repo specifically — alkcall has *no* `fuzz/`
+workspace today and its tests are inline `#[cfg(test)]` modules, so
+colocated checks fit the house style. But it adds a dependency and an
+engine-selection layer between the code and cargo-fuzz, and none of the
+RPC-protocol crates surveyed (quinn, rustls, prost, h2) use it. The
+deciding factor: alkcall's highest-value targets are *async* (the framing
+reader and demux loop are tokio-generic), and bolero's in-process test
+form adds friction there (`#[tokio::test]` cannot drive `bolero::check!`
+iteration without shims). Recommendation: start with a standard `fuzz/`
+workspace; if corpus-replay-as-unit-test proves valuable later, adopting
+bolero's pattern (or just hand-rolling a corpus-replay test, which quinn
+does in plain `cargo test`) is a cheap follow-up. Note quinn's CI already
+does plain corpus replay without bolero — that pattern is available
+without any new dependency.
+
+**Not adopted: libafl, honggfuzz, OSS-Fuzz (initially).** libafl is a
+framework for bespoke fuzzers — unnecessary for parser targets. honggfuzz
+is superseded. OSS-Fuzz is a strong *later* step once targets exist and
+have been stable for a while (it is free continuous fuzzing and expects
+exactly this target layout; both rustls and prost are on it).
+
+**Sanitizer choice:** default `--sanitizer=address` with debug assertions
+(cargo-fuzz's default config, `-O1`). MSAN is not warranted — with zero
+`unsafe` there is no uninitialized-memory class; ASAN mainly adds
+heap-buffer-overflow detection for slice math in hand-rolled framing and
+double-free-style issues in vendored types, plus the debug-assertions
+panic tripwire, which is the real detector here.
+
+---
+
+## 5. alkcall's untrusted-input parse surfaces (inventory)
+
+Verified against the code (file:line as of 0.8.0). The crate is safe Rust
+end-to-end: **zero `unsafe` blocks** (grep-verified). Two wire formats,
+plus JSON-based op payloads:
+
+| # | Surface | Location | Sync? | Notes |
+|---|---|---|---|---|
+| 1 | `EventEnvelope` framing decode | `src/protocol/wire.rs:204-232` | async (`read_frame`, generic over `AsyncRead`; tests already drive it with `std::io::Cursor`) | 4-byte BE length prefix; rejects len 0 and len > `MAX_FRAME_SIZE` (64 MiB) **before** `vec![0u8; length]` at `:221`; partial prefix/body handled (`ConnectionClosed`); serde_json parse of up to 64 MiB body. |
+| 2 | Channels chunk header | `src/channels/wire.rs:96-112` (`parse_header`) | **sync, pure, no allocation** | `len >= 8` check, `length > MAX_CHUNK_LEN` (16 MiB) rejected before payload exists. `write_header` at `:123`. |
+| 3 | Demux loop | `src/channels/adapter.rs:126-222` (`run_demux_loop_for_client`, pub) | async | `parse_header` → bounded alloc (`:181`) → `route_payload`; `TooLarge` branch skips in 64 KiB reads with a cumulative 256 MiB budget (`:137`, `:153-170`) instead of allocating; EOF → `clear_all`. |
+| 4 | `ChannelManager` routing | `src/channels/manager.rs:439-457` (`route_payload`), `:463-485` (`park_early_arrival`) | async (bounded send await) | Unknown ids park up to `EARLY_ARRIVAL_CAP = 64` chunks per id; **the map's key-space is unbounded** (see §6.2). |
+| 5 | Spec rebuild from wire | `src/client/from_call.rs:209-310` (`rebuild_spec_for`, `pub(crate)`, sync pure) | sync | Remote-announced op specs: op_type/visibility/access_control/error_schemas/`publish_schema` — attacker-shaped JSON becomes compiled `jsonschema` validators at registration. |
+| 6 | `op/register` DTO | `src/registry/op_register.rs:66-84` (`OpRegisterRequest::from_json`, `pub`, sync pure) | sync | Wraps `rebuild_spec_for` + replace flag. |
+| 7 | Pending-request state machine | `src/protocol/pending.rs:111-229` (sync, `pub`) | sync | `handle_responded/completed/aborted/error`, eviction. |
+| 8 | Abort cascade | `src/protocol/abort.rs:46` (`cascade_abort`, sync pure) | sync | Tree walk; O(n²) descendant search (§6.2). |
+| 9 | Dispatch payload parsing | `src/protocol/dispatch.rs:341-412` (`dispatch_start`), `:646-770` (`pump_sink`), `:897-1027` / `:1120-1250` (single-stream loops) | sync-prefix / async | `payload.get(...)` extraction, `forwarded_for` as `serde_json::from_value::<Identity>`, `call.error` → `CallError`, jsonschema validation of published chunks. |
+| 10 | Client-side envelope pump | `src/protocol/connection.rs:693-741` (`read_single_stream_until_closed`, `dispatch_envelope`) | async | pub; decode → pending-resolution pump. |
+| 11 | Channel lifecycle ops | `src/channels/operations.rs:182-272` (close/control handlers) | async | `as_u64` → `as u32` cast truncation on `channel_id`. |
+| 12 | Relay reply parsing | `src/channels/relay.rs:239-297` (`open_on_producer_leg`), `:308-335` (`map_spoke_error`) | async | reply `channel_id` extraction, `details.reason/message`. |
+
+Also relevant: **`jsonschema` is compiled from schemas that arrive from
+the wire** (`from_call.rs:299-303` announced `publish_schema` /
+`input_schema`; enforced per chunk at `dispatch.rs:706-718`,
+`registration.rs:257-274`) — a compilable-but-pathological remote schema
+is a CPU-amplification class the fuzz campaign can probe.
+
+Non-surfaces (deliberately): no TTY/SFTP/varint parsers in this crate; the
+channels layer carries opaque `Bytes` and the handler owns sub-stream
+framing (ADR-035) — those downstream parsers are downstream crates' fuzz
+targets.
+
+---
+
+## 6. Findings the campaign should target (candidate issues in current code)
+
+These are pre-fuzzing code-review findings (mine, verified at 0.8.0) that
+define what the fuzz targets must encode as invariants. They are also, in
+effect, the first candidates for the fuzzer to confirm or refute.
+
+### 6.1 Framing and parse invariants (encode as assertions in targets)
+
+1. **No-panic on any byte sequence** for both framing paths and all sync
+   pure parsers — the baseline every target asserts by existing.
+2. **Consumption accounting** — `read_frame` consumes exactly
+   `4 + length` bytes for a valid frame; `parse_header` reads exactly 8.
+3. **Round-trip** — envelope encode→decode (structural equality; note
+   serde_json runs **without** `preserve_order` in this crate's dep tree,
+   so `Value` object key order is not preserved — byte-identity round-trip
+   asserts are invalid for envelopes; use structural equality); chunk
+   header encode→decode identity.
+4. **Allocation bounds** — decode paths never allocate more than
+   `MAX_FRAME_SIZE` / `MAX_CHUNK_LEN` for any input.
+5. **Termination** — demux skip loop obeys the 256 MiB budget and always
+   terminates on a trickle-feed peer.
+
+### 6.2 DoS-class candidate findings (pre-fuzz code review)
+
+1. **Unbounded early-arrival key-space** — `ChannelManager.early_arrivals`
+   (`src/channels/manager.rs:102`, `park_early_arrival` `:463-485`) caps
+   parked chunks **per key** at 64, but nothing bounds the number of
+   distinct never-adopted `channel_id` keys. A peer spraying unknown ids
+   parks up to 64 chunks × up to 16 MiB *per distinct id* until
+   `clear_all` at EOF — an OOM class on a long-lived connection. A fuzz
+   target driving `route_payload` with arbitrary ids and payloads, with a
+   total-bytes-parked assertion, will find this class immediately.
+2. **Unbounded per-connection task accumulation** — `spawned: Vec<JoinHandle>`
+   (`src/protocol/dispatch.rs:894-895`, pushed at `:914`, drained only at
+   loop end `:1030-1032`, and the channel-0 twin `:1115-1118`,
+   `:1253-1255`): one task per inbound `call.requested`, no cap on
+   concurrent requests per connection. Cheap-request spam grows the
+   vector unboundedly for the connection's life.
+3. **64 MiB pre-payload allocation window** — `read_frame` allocates
+   `vec![0u8; length]` after validating ≤ 64 MiB but *before reading any
+   payload byte* (`src/protocol/wire.rs:217-221`): repeated 4-byte
+   headers force repeated 64-MiB zeroing (allocation-rate pressure).
+   Bounded per frame, but worth a target asserting decode never
+   allocates beyond the cap and exploring whether a read-into-capped-
+   buffer refactor (libp2p gossipsub's validate-without-allocating
+   pattern) is warranted.
+4. **O(n²) abort cascade** — `find_descendants` scans the full pending map
+   per frontier step (`src/protocol/abort.rs:80-104`); many pendings + an
+   abort = quadratic CPU. An op-sequence target on `PendingRequestMap` +
+   `AbortCascade` with many registered requests will surface it.
+5. **Remote-schema CPU amplification** — compiled-from-wire jsonschema
+   validators applied per published chunk (§5); pathological-schema
+   generation is a semantic fuzz target.
+
+Items 1 and 2 are the strongest arguments that fuzzing (specifically
+*stateful*, not just parser-level fuzzing) is warranted here: they are
+resource-bound bugs in correct-looking safe Rust that example-based tests
+structurally cannot find, in code paths every downstream consumer exposes
+to peers.
+
+---
+
+## 7. Recommendation
+
+### 7.1 Adopt fuzzing; scope it to the wire surface
+
+Create `fuzz/` via `cargo fuzz init` (cargo-fuzz ≥ 0.13; keep the fuzz
+crate in the main workspace, its default since 0.11.4), add `fuzz/` and
+`fuzz/artifacts/` to `.gitignore`, add `"fuzz"` handling to the publish
+exclude list if needed (cargo-fuzz's generated layout is already
+workspace-compatible). Add five targets, in priority order:
+
+| # | Target | Input style | Drives | Invariants |
+|---|---|---|---|---|
+| 1 | `chunk_header` | raw `&[u8]` | `parse_header` / `write_header` (`channels/wire.rs`) | no-panic; round-trip identity; `TooLarge` iff `len > MAX_CHUNK_LEN`; consumption accounting (8 bytes) |
+| 2 | `envelope_frame` | raw `&[u8]` | `FrameFramedReader::new(Cursor::new(bytes)).read_frame()` under a current-thread runtime's `block_on` (tests already use `Cursor`, `wire.rs:534`) | no-panic; never allocates > `MAX_FRAME_SIZE`; clean `FrameError` on truncation/oversize/zero-length; consumption accounting |
+| 3 | `manager_routing` | op-sequence: `#[derive(Arbitrary)]` enum over `{ route_payload(id, bytes), adopt, teardown, clear_all, … }` | `ChannelManager` | **total parked-bytes bound** (§6.2-1); no-panic; id-uniqueness invariants |
+| 4 | `envelope_semantic` | `#[derive(Arbitrary)]` envelope-shaped input | constructors → `write_frame` → `read_frame` round-trip | structural round-trip; `CallError` payload parse never panics |
+| 5 | `spec_parse` | raw bytes → `serde_json::Value` → `rebuild_spec_for` / `OpRegisterRequest::from_json` | sync pure parsers | no-panic; registration always `Result`; round-trip vs `spec_to_json_pub` |
+
+Second wave (after the first five stabilize, roughly in quinn's
+`streams.rs` style): a pending-map/abort op-sequence target (§6.2-4), a
+demux-loop byte-sequence target through `run_demux_loop_for_client`
+(needs a small current-thread runtime and a spawned mux runner), and a
+client-pump target on `read_single_stream_until_closed`.
+
+**Corpus policy: commit hand-made seeds, gitignore grown corpora** (the
+quinn/h2 pattern). Seeds per target: valid frame/header, truncation at
+every prefix length, `length = 0`, `length = MAX+1`, `length = u32::MAX`,
+channel 0, invalid UTF-8 in JSON, deep-ish nesting. libFuzzer runs fine
+without seeds but is far more efficient on structured inputs. Seed
+generation can be scripted from existing unit tests (quiche's
+`gen_fuzz_seeds.sh` pattern).
+
+**Where internals need exposure:** follow quinn/rustls — `#[cfg(fuzzing)]
+pub mod fuzzing` modules re-exporting `pub(crate)` items
+(`rebuild_spec_for`) rather than widening the public API. The crate
+already has `pub` sync parsers (`parse_header`, `from_json`,
+`PendingRequestMap`), so exposure needs are small.
+
+### 7.2 CI: two-tier, rustls-style
+
+1. **Per-push smoke** (cheap, catches build rot and shallow bugs): pinned
+   nightly toolchain + pinned cargo-fuzz; `cargo fuzz build`; then per
+   target `cargo fuzz run <t> -- -max_total_time=10` (rustls's exact
+   budget) in a small matrix; upload `fuzz/artifacts` on failure.
+2. **Scheduled campaign** (weekly at first; cron-driven Actions workflow):
+   `-max_total_time=1800` (30 min) per target with a cached corpus
+   (Actions cache, `restore-keys` prefix matching) and `-fork=$(nproc)`;
+   grow corpora incrementally. This is the depot.dev pattern; adopt it
+   only after the smoke tier is green for a while.
+3. **No-cargo-fuzz fallback for PRs**: since nightly is a dedicated-job
+   concern, an even cheaper PR gate is `cargo test --manifest-path
+   fuzz/Cargo.toml` (replays the committed corpus through the targets as
+   plain unit tests — quinn's CI does this; corpus replay costs nothing
+   and prevents seed rot).
+
+libFuzzer flags worth pinning in the targets' run configs:
+`-rss_limit_mb=2048` (the OOM tripwire — directly relevant to §6.2-1/3),
+`-max_len=65536` on framing targets, `-timeout=25` (well under CI job
+limits), `-use_value_profile=1` (helps get past length/JSON-prefix
+comparisons), and a `-dict` of JSON tokens for the envelope targets.
+
+### 7.3 What not to do
+
+- **Do not** gate regular development on nightly: fuzz tooling lives
+  entirely in `fuzz/` + the fuzz CI job; `cargo test` / MSRV / wasm
+  targets are untouched.
+- **Do not** assert byte-identity round-trips for `Value` payloads
+  (serde_json without `preserve_order` sorts object keys — structural
+  equality only). This would generate false positives from day one.
+- **Do not** commit grown corpora to git at first (quinn/h2 model);
+  revisit if the scheduled campaign produces inputs worth curating.
+- **Do not** reach for libafl/OSS-Fuzz/Mayhem until the five initial
+  targets are stable; OSS-Fuzz onboarding is the natural next step after
+  that (free continuous fuzzing, expects exactly this layout).
+
+### 7.4 Sequencing
+
+1. `cargo fuzz init` + first two targets (`chunk_header`, `envelope_frame`)
+   — highest value, lowest setup (both are thin wrappers over existing
+   sync/`Cursor`-drivable APIs). **Done — see §7.7.**
+2. Run a local 10–30 min campaign per target **via the detached runner
+   (§7.6 — never in the foreground of an agent session)**; fix anything
+   found; triage §6.2 candidates with targeted corpus entries.
+   **Done for targets 1–2 — see §7.7.**
+3. Add targets 3–5, the smoke CI job, and `.gitignore` entries.
+   **Targets 3–5 done, campaigns clean — see §7.8. The CI job will not
+   exist — see §7.9 (no hosted CI policy); the stable-side corpus
+   replay `cargo test --manifest-path fuzz/shared/Cargo.toml` is in
+   the release verification checklist instead (AGENTS.md).**
+4. ~~Scheduled campaign tier; then OSS-Fuzz application.~~ **Not
+   planned — see §7.9.** Long campaigns are run manually via the
+   detached runner (§7.6) when wanted; OSS-Fuzz is out (it requires
+   hosted infrastructure and a public repo posture this project does
+   not have).
+
+### 7.5 Relationship to existing tests
+
+The existing suite is strong on *valid-input* round-trips and documented
+error paths (framing tests at `wire.rs:262-588`, demux skip tests at
+`adapter.rs:279-693`, spec round-trips at `from_call.rs:634-1053`). What
+no example-based suite provides, and what fuzzing adds:
+
+- random *malformed* input exploration (the quinn CVE class),
+- stateful interleavings (many ids × many ops, the §6.2-1/2 classes),
+- resource-bound assertions under unbounded adversarial sequences.
+
+Two zero-cost complements, available without any new toolchain: (a) replay
+committed corpora as unit tests in normal CI (quinn's pattern — add it
+from day one, it is two lines of CI); (b) a quickcheck-style round-trip
+property test for the chunk header (yamux's pattern) if the team wants
+in-suite fuzz-adjacent coverage without nightly. Both are optional
+nice-to-haves; the core recommendation is the `fuzz/` workspace.
+
+### 7.6 Operational isolation: fuzzing must never share fate with the agent session
+
+This one is an environment constraint, not a nice-to-have. Agent sessions
+(opencode) run fuzzer builds/campaigns through a bash tool that spawns the
+fuzzer as a **child of the session's own process tree and cgroup**. A fuzz
+run is precisely the workload shape that kills its own host:
+
+- **OOM-killer shared fate**: the target's worst case *is* unbounded
+  allocation (that's what §6.2-1/3 look for). If libFuzzer's own RSS guard
+  is miscalibrated or races the kernel, the kernel OOM killer fires — and
+  it picks the largest-RSS process in the *cgroup*, which can be the
+  opencode server hosting the session, killing the agent mid-run. An
+  OOM in a fuzz target must cost the fuzzer, never the session.
+- **Fork bombs and CPU saturation**: `-fork=N` mode spawns many workers;
+  a runaway campaign or a buggy target with unbounded task spawning can
+  starve the session host's CPU/IO.
+- **Interactive-shell edge cases**: libFuzzer prints status lines that
+  confuse non-TTY shells; a crashed fuzzer must never leave the tool's
+  bash session hanging.
+
+Three layers of defense, all standard, cheapest first:
+
+1. **libFuzzer's own soft limits (always on)**: `-rss_limit_mb=2048` +
+   `-malloc_limit_mb=2048` make libFuzzer *exit cleanly* (report the
+   input as OOM-class artifact) when the target exceeds the budget, before
+   the kernel gets involved. This is the primary defense and it is
+   already part of the §7.2 flag set. Note the libFuzzer RSS limit is
+   **soft** (it polls `/proc/self/statm` in a background thread and
+   exits), not a hard rlimit — a fast single huge allocation can still
+   beat it; that's what layers 2–3 are for. Do **not** use `ulimit -v`
+   with ASAN/MSAN (the sanitizer reserves terabytes of virtual address
+   space; the classic failure mode is immediate `MmapAlloc` death) — the
+   equivalent knob under ASAN is `malloc_limit_mb`, and libFuzzer's
+   documented recipe for hard-limiting RSS under sanitizers is `-fork=1`
+   (see next item).
+2. **Fork mode as the blast-radius containment (default for local
+   campaigns)**: `-fork=1` (or `$(nproc)`) runs each input in a short-
+   lived child process. A target crash, timeout, OOM, or leak kills only
+   that one-shot child; the parent harness survives, records the artifact,
+   and keeps fuzzing. This is libFuzzer's own documented containment
+   model — and it is mutually exclusive with in-process ASAN crash
+   reporting (the child still detects, the parent persists the evidence).
+   Fork mode also solves the *other* shared-fate trap: a target that
+   deadlocks no longer hangs the campaign (per-input timeout kills the
+   child, not the session's bash call).
+3. **Process detachment from the session tree (mandatory for agent-run
+   campaigns)**: agent sessions must never run fuzzing as a foreground
+   child. The runner script below wraps `cargo fuzz run` in
+   `setsid` + `nohup` + stdin/stdout/stderr redirection to a log file,
+   which (a) removes the fuzzer from the session's controlling terminal
+   and signal-relation, (b) makes the run survive the session ending, and
+   (c) gives the agent a pollable log/artifact tail instead of a blocking
+   call. Combined with fork mode, an OOM-class finding costs one child
+   process; combined with the soft RSS limit, the kernel OOM killer should
+   never be the discovery mechanism at all.
+
+The detached-runner recipe for agent sessions (write as
+`fuzz/run-detached.sh` in the implementation step, not inline in a tool
+call):
+
+```bash
+#!/usr/bin/env bash
+# Detached fuzzing runner for agent sessions: the fuzz campaign never
+# runs as a foreground child of the session (OOM in a target must not
+# take down the agent host), and survives the session ending.
+set -euo pipefail
+target="${1:?usage: run-detached.sh <target> [extra libfuzzer args...]}"
+shift
+runtime="${FUZZ_RUNTIME_SECS:-600}"
+log="fuzz/artifacts/${target}-$(date -u +%Y%m%d-%H%M%S).log"
+mkdir -p fuzz/artifacts
+setsid nohup cargo fuzz run "$target" -- \
+  -fork=1 -rss_limit_mb=2048 -malloc_limit_mb=2048 -timeout=25 \
+  -max_total_time="$runtime" "$@" \
+  >"$log" 2>&1 < /dev/null &
+echo "pid=$! log=$log"
+```
+
+Polling protocol for the agent: `tail -n 50 fuzz/artifacts/<target>-*.log`
+and check `fuzz/artifacts/` for `crash-*`/`oom-*`/`timeout-*` files
+periodically; `pgrep -f "cargo fuzz run <target>"` to see if it is still
+running. Never `wait` on the detached process from a tool call — poll
+instead. One session can hold one detached campaign per target; the log
+filename carries the UTC timestamp.
+
+**For CI the constraint does not apply** (the runner *is* the job), but
+the same flags apply everywhere: `-rss_limit_mb`/`-malloc_limit_mb` and
+`-fork=1` should be pinned in the target run configs in both the smoke
+tier and the scheduled campaign. For the scheduled campaign tier, also
+cap concurrency (`-fork=$(nproc)` is fine on CI runners; locally prefer
+an explicit number well below core count) and keep the Actions-job
+timeout above the `-max_total_time` budget so a wedged harness is killed
+by the runner, not the host.
+
+---
+
+## 7.7 Implementation status (step 1 of §7.4, 2026-09-27)
+
+**Adopted.** The `fuzz/` workspace exists with targets 1 and 2 from
+§7.1, committed seed corpora, the detached runner, and stable-side
+corpus replay. Everything below is verified in-tree.
+
+### Layout (as implemented)
+
+```
+fuzz/
+├── Cargo.toml            alkcall-fuzz (nightly-only bins; own [workspace])
+├── rust-toolchain.toml   pins nightly for this subtree only
+├── fuzz_targets/
+│   ├── chunk_header.rs   thin fuzz_target! wrapper
+│   └── envelope_frame.rs thin fuzz_target! wrapper
+├── shared/               alkcall-fuzz-shared — STABLE-toolchain library
+│   └── src/{chunk_header,envelope_frame}.rs  invariant logic + corpus replay
+├── corpus/{chunk_header,envelope_frame}/     committed seeds (245 total)
+├── gen_fuzz_seeds.py     deterministic seed generator (quiche pattern)
+├── run-detached.sh       §7.6 detached runner (CWD-independent)
+├── json.dict             JSON token dictionary for envelope targets
+└── README.md
+```
+
+Deviations from the §7.1 sketch, all load-bearing:
+
+- **The invariant logic lives in `fuzz/shared/` (a separate
+  stable-toolchain crate), not inline in the target binaries.** This
+  makes §7.2's tier-3 fallback (corpus replay as plain `cargo test`)
+  real from day one: `cargo test --manifest-path fuzz/shared/Cargo.toml`
+  replays every committed seed through the identical invariant functions
+  the fuzzer runs, on stable, in normal CI. The `fuzz_target!` binaries
+  are three-line wrappers.
+- **The root `Cargo.toml` gained a `[workspace]` table
+  (`members = ["."]`, `exclude = ["fuzz"]`)** and `"fuzz/"` joined the
+  publish `exclude` list. Without the explicit workspace table, cargo
+  auto-discovers `fuzz/shared/` into the main workspace and the MSRV
+  toolchain tries to build the nightly-consumed dev-deps.
+- **`fuzz/rust-toolchain.toml` pins `nightly`** for the fuzz subtree so
+  `cargo fuzz build` works from any CWD (rustup resolves toolchains per
+  directory; the initial build attempt from the repo root picked the
+  stable toolchain and failed on `-Zsanitizer`). Nightly remains
+  confined to `fuzz/` — the crate itself stays stable at MSRV 1.88.
+- **No `#[cfg(fuzzing)]` exposure was needed.** Both target APIs were
+  already `pub`: `parse_header`/`write_header` (`channels/wire.rs`) and
+  `FrameFramedReader`/`FrameFramedWriter` (`protocol/wire.rs`). The one
+  private item, `MAX_FRAME_SIZE` (`wire.rs:20`), is a wire-stable
+  constant (ADR-014), so the shared crate carries its own copy
+  (16 MiB/64 MiB are one-way-door values; a drift would be caught by the
+  shape invariants, which assert the rejection boundary).
+- **Seeds are committed** (245 files), gitignored artifacts/corpus-grown
+  per the generated `fuzz/.gitignore`; the generator script
+  (`gen_fuzz_seeds.py`) is committed next to them.
+
+### Invariants encoded (beyond the §7.1 table)
+
+`chunk_header`:
+- no-panic; round-trip identity (`write_header(parse_header(x)) ==
+  x[..8]`); `TooLarge` iff `length > MAX_CHUNK_LEN` with the parsed
+  `length` echoed in the error; `HeaderTooShort` iff `< 8` bytes with
+  exact `need`/`have`; `is_eof() == (length == 0)`; consumption
+  accounting (8 bytes); **input buffer never mutated**.
+
+`envelope_frame`:
+- no-panic; clean error classes with **shape assertions** on each
+  `FrameError` variant: `ConnectionClosed` only when the prefix is
+  truncated or the body is short (a complete body must never yield it);
+  `InvalidFrame` only for `len == 0` or `len > MAX_FRAME_SIZE`;
+  `Json` only when the full body was present; `Io` impossible on a
+  Cursor; Ok only when `len > 0`, `len <= MAX`, body complete.
+- allocation bound: the reader never allocates for `len > MAX_FRAME_SIZE`
+  or `len == 0` (rejection precedes `vec![0u8; length]` — verified by the
+  `InvalidFrame`/Ok shape partition).
+- exact consumption accounting (4 + len bytes read for a valid frame).
+- structural round-trip: every decodable envelope re-encodes via
+  `write_frame` and re-decodes to an equal envelope (structural —
+  serde_json without `preserve_order` does not preserve key order).
+- serde contract: the decoded envelope serializes with `type`/`id`/
+  `payload` keys intact (`type` survives the rename).
+- **trailing-byte probe**: for any input ending in a complete JSON
+  object body, a copy with one extra byte appended *and counted in the
+  length prefix* must fail with a `Json` error (serde_json's
+  from_slice rejects trailing non-whitespace) — catching any future
+  switch to a streaming/tolerant reader that would silently accept
+  junk after the JSON document.
+
+Note on the probe: the length prefix counts **only the body**, not the
+4-byte prefix — the first probe draft claimed `4 + len + 1` and tripped
+its own shape assert (`ConnectionClosed`). The fuzzer would have found
+that instantly; corpus replay found it first.
+
+### Verification at adoption
+
+- `cargo fuzz build` clean (nightly-1.95.0-nightly, cargo-fuzz 0.13.2,
+  libfuzzer-sys 0.4.13).
+- Stable side untouched and green: `cargo test` 682 passed / 0 failed;
+  `cargo clippy --all-targets -- -D warnings` clean; `cargo fmt --check`
+  clean (main crate, fuzz workspace, and fuzz/shared).
+- Corpus replay (`cargo test --manifest-path fuzz/shared/Cargo.toml`):
+  245 committed seeds through both invariant sets, green.
+
+Commit: 80a37e9 (step-1 implementation, before the campaigns below ran).
+
+### Campaign results (10-min detached runs per target, §7.6 runner)
+
+**No crashes, no hangs, no leak/OOM findings.** Both campaigns ran to
+their time budget via `run-detached.sh` and exited 0 (`-fork=1
+-rss_limit_mb=2048 -malloc_limit_mb=2048 -timeout=25`;
+`-max_len=65536 -dict=json.dict` for the envelope target); artifact
+directories empty after both.
+
+- `chunk_header` — saturated its state space in the first seconds and
+  spent the remaining ~10 min confirming stability: flat
+  `cov: 51 ft: 54` from job ~5 onward, 203.9M execs at ~350k exec/s,
+  `oom/timeout/crash: 0/0/0` on all 33 fork jobs. The pure-8-byte-parser
+  ceiling is fully enumerated.
+- `envelope_frame` — still finding coverage when the budget ended:
+  2119 edges / 7246 features / 1664 in-memory corpus entries
+  (from the 245 committed seeds), ~7.08M execs at ~12k exec/s,
+  `oom/timeout/crash: 0/0/0` on all 33 fork jobs. Growth was still
+  positive (JSON structure exploration), so longer campaigns keep
+  paying; the 25 s timeout and both memory tripwires never fired.
+
+The grown envelope corpus (1631 new entries) was **not** merged into
+the committed seeds — per the §7.1 policy, grown corpora stay
+gitignored; worth revisiting if a future scheduled campaign produces
+inputs worth curating. §6.2-3 (pre-payload allocation window) remains
+bounded as designed. §6.2 items 1/2/4/5 are stateful targets
+(§7.4 step 3) and were not exercised by these parser-level campaigns.
+
+---
+
+## 7.8 Step 3: targets 3–5 (2026-09-27)
+
+**Adopted.** Three more targets, all over already-`pub` APIs (the
+`#[cfg(fuzzing)]` exposure never materialized — quinn/rustls-style
+exposure has not been needed for any of the five targets):
+
+| Target | Drives | Invariants |
+|---|---|---|
+| `manager_routing` | `ChannelManager` under `#[derive(Arbitrary)]` op sequences (`Route`/`Open`/`Adopt`/`Teardown`/`ClearAll`), 256 ops × 4 KiB payloads, live mux runner, drainer tasks | no-panic; **exact counter models**: harness parked/dropped counters must equal the manager's monotonic `early_arrival_count`/`dropped_unknown_chunks` after every op; parked bytes ≤ distinct-ids × 64 × 16 MiB (the documented per-channel bound, §6.2-1); post-sequence `clear_all` reconciles every routed byte against the drainers' totals (lossless bounded-buffer routing, sentinel semantics included) |
+| `envelope_semantic` | `#[derive(Arbitrary)]` `EnvelopeKind` → the six `EventEnvelope` constructors → serde round-trip → `write_frame`/`read_frame` | no-panic; constructors emit exactly the wire-stable event-type constants; any `Value` payload survives a serde round-trip; `call.error` payloads always parse back as `CallError` (ADR-016 closed schema); structural `write_frame`/`read_frame` round-trip |
+| `spec_parse` | raw bytes → `serde_json` → `OpRegisterRequest::from_json` (the `pub` wrapper over `rebuild_spec_for`) → `OperationRegistry::register` (attacker-shaped schemas **compile at registration**, CF-003) | no-panic; parse failures are clean `INVALID_INPUT`; `spec_to_json_pub` → `from_json` round-trips the rebuilt spec; registration is always `Result` (uncompilable schema = compile error, never silent); registry bookkeeping survives repeated attacker-shaped inserts |
+
+New supporting pieces: `fuzz/shared/src/arbitrary_value.rs` (a bounded
+`Arbitrary` impl for `serde_json::Value` — depth 6, width 6, sized
+strings/keys), and 20 `spec_parse` + 4 `manager_routing` committed
+seeds (the op-sequence corpus is tiny because structured `Arbitrary`
+inputs self-generate; the four committed seeds are semantic fixtures
+including the duplicate-adopt sequence that pinned the bug below).
+
+### First real finding: duplicate adopt/open destroyed the live channel
+
+The `manager_routing` campaign found it in its first minutes — the
+§6.2 stateful thesis, confirmed: **the bug is invisible to
+example-based tests** because it needs an *interleaving* (adopt → drop
+write half → duplicate adopt → route) that no unit test thinks to
+replay.
+
+**Mechanism** (`src/channels/manager.rs`, `open_channel` and
+`adopt_channel`, pre-fix):
+
+```rust
+if channels.insert(channel_id, state).is_some() {
+    return Err(ManagerError::ChannelExists(channel_id));
+}
+```
+
+`HashMap::insert` **replaces** an occupied entry and returns the old
+value — so the collision-detection idiom silently *installed the new
+state and dropped the old `ChannelState`*, whose `demux_sender` was
+the live channel's read half. A duplicate `adopt_channel`/`open_channel`
+on an in-use id returned `Err(ChannelExists)` (correct) **while
+destroying the live channel** (incorrect): readers saw a spurious EOF,
+subsequently routed chunks were lost, and the mux write half kept
+framing onto the transport for a channel the demux no longer fed.
+
+Reproducibility: a failed adopt on a live channel whose mux pump had
+finished (the write half dropped — as any caller does) re-registered a
+pump, succeeded through `mux.register`, and hit the replacing insert.
+The duplicate-adopt path is reachable whenever an open-op response is
+replayed or a connection-owner race re-announces an id.
+
+**Fix** (this commit): check `channels.contains_key(&channel_id)` and
+return before any insert — the map is never touched on collision in
+either `open_channel` or `adopt_channel`. Regression tests:
+`adopt_channel_duplicate_id_leaves_live_channel_intact`,
+`open_channel_duplicate_id_leaves_live_channel_intact` (both verify
+routing survives a rejected duplicate; the first also verifies the
+EOF sentinel remains the only EOF source).
+
+**Also fixed in the harness** (fuzzer-vs-harness findings, not crate
+bugs): `clear_all` returns the opener-ledger entries (ADR-047 §7),
+not channel-map entries — adopted channels carry no ledger entry, so
+`drained.len() == open_count()` is *not* an invariant; the monotonic
+counters survive `clear_all`; and drainer-byte reconciliation needs
+per-id supersession when a fresh stream replaces a drained one.
+
+### Campaign results (10-min detached runs per target, §7.6 runner)
+
+The smoke-tier runs above surfaced two harness-model defects worth
+recording (the fuzzer as a harness-checker), fixed before the long
+runs: the op-sequence driver's EOF-sentinel latch is **per-receiver,
+not per-channel-id** — a fresh adopt installs a fresh reassembled
+stream with no latched EOF, while a sentinel inside a *drained
+early-arrival queue* latches the new receiver too
+(`drain_early_arrivals` delivers it); and `Adopt` ops must respect
+ADR-047 §5's odd/even split (an Accept-side manager adopts the peer's
+odd ids; its own `Open` allocates even — a cross-range adopt/open
+collision is a protocol violation, not a manager bug).
+
+**Final 10-minute detached campaigns, all three targets (post-fixes,
+post the `insert`-replace fix): every run exited 0 with an empty
+artifacts directory — no crashes, hangs, OOMs, or leaks.**
+
+- `manager_routing` — 1.06M execs (~1.9k exec/s; each exec replays up
+  to 256 manager ops on a live runtime), 33 fork jobs clean,
+  `oom/timeout/crash: 0/0/0` throughout. Final coverage 2499 edges /
+  11332 features / 461 in-memory corpus entries. The exact-counter and
+  parked-bytes invariants held across every adversarial sequence.
+- `envelope_semantic` — 2.44M execs (~4.4k exec/s), 33 fork jobs
+  clean, coverage saturated at 1669 edges (constructor × payload shape
+  space is finite), corpus 765. All six event kinds round-tripped
+  structurally; `CallError` parse-back never failed.
+- `spec_parse` — 10.8M execs (~19k exec/s), 33 fork jobs clean,
+  coverage 978 edges / corpus 1267. The registry compiled every
+  attacker-shaped schema it was handed (or rejected cleanly); the
+  `spec_to_json_pub` → `from_json` round-trip never diverged.
+
+§6.2-1 (parked-bytes bound) is now encoded as an exact counter model
+and held; §6.2-3 confirmed bounded at the parser level (§7.7). The
+stateful coverage §7.4 step 3 called for exists and is clean.
+
+---
+
+## 7.9 No hosted CI — the standing policy (2026-09-28)
+
+§7.2's two CI tiers (per-push smoke, scheduled campaign) and the
+OSS-Fuzz step assume a hosted CI platform. This repo has none and will
+not get one: the git host is a minimal gitea that serves git and
+nothing else, deliberately — gitea/gitlab have had full-compromise CVEs
+(app.ini and any plaintext DB tokens exfiltrated in one real incident
+elsewhere), so the attack surface stays minimal. All verification and
+campaigns are **manual, run from the separate publishing server**:
+
+- **Corpus replay is the fuzz gate, as plain `cargo test`:**
+  `cargo test --manifest-path fuzz/shared/Cargo.toml` replays every
+  committed seed through the same invariant functions the fuzzer runs
+  — on stable, no nightly, no cargo-fuzz. It is part of the release
+  verification checklist (AGENTS.md). This is CI tier 3's deliverable
+  (§7.2), minus the automation.
+- **Campaigns** run via the detached runner (§7.6) when wanted —
+  e.g. before a release, or after touching `src/protocol/wire.rs`,
+  `src/channels/wire.rs`, the demux loop, or `ChannelManager`.
+- **OSS-Fuzz is out**: it requires hosted infrastructure and a public
+  repo posture this project does not have.
+- Do not add Actions/Gitea-Actions/workflow files anywhere in this
+  repo, and do not reintroduce "when CI exists" language into docs —
+  point at this section instead.
+
+## 8. Answering the "if / how" directly
+
+- **If?** Yes — justified by position in the dependency graph, two stable
+  attacker-reachable wire formats, and two concrete DoS-class findings a
+  fuzz campaign would have caught (§6.2). The expected bug classes here
+  are panics and resource exhaustion, not memory unsafety (no `unsafe`
+  exists), which is precisely the profile where cheap fuzzing pays off.
+- **How?** `cargo-fuzz` + `arbitrary`, a standard `fuzz/` workspace with
+  five targets (§7.1), committed seed corpora only, `#[cfg(fuzzing)]`
+  internals exposure where needed, two-tier CI with a 10 s-per-target
+  smoke on every push (§7.2), nightly confined to the fuzz job, AFL as an
+  optional secondary engine, bolero deferred, OSS-Fuzz after
+  stabilization. **Locally (agent sessions), campaigns always run via the
+  detached runner (§7.6): `setsid` + `nohup` + log file + poll, fork mode
+  on, soft RSS/malloc limits pinned — an OOM in a fuzz target must cost
+  the fuzzer, never the agent session.**
+
+## 9. References
+
+- RUSTSEC-2026-0037 / CVE-2026-31812 (quinn-proto remote DoS; maintainers'
+  fuzzing-coverage statement) — https://rustsec.org/advisories/RUSTSEC-2026-0037.html
+- cargo-fuzz releases / Rust Fuzz Book — https://github.com/rust-fuzz/cargo-fuzz ·
+  https://rust-fuzz.github.io/book/
+- arbitrary 1.4.2 and the 2025 speed analysis —
+  https://nnethercote.github.io/2025/08/16/speed-wins-when-fuzzing-rust-code-with-derive-arbitrary.html
+- rustls fuzz targets + CI — https://github.com/rustls/rustls/tree/main/fuzz ·
+  https://github.com/rustls/rustls-fuzzing-corpora
+- quinn fuzz targets (packet/streams/params) — https://github.com/quinn-rs/quinn/tree/main/fuzz
+- quiche fuzzing + seed generation — https://github.com/cloudflare/quiche/tree/master/fuzz
+- h2 MockIo e2e target — https://github.com/hyperium/h2/tree/master/fuzz
+- prost fuzz (libfuzzer + AFL, FUZZING.md) — https://github.com/tokio-rs/prost/tree/master/fuzz
+- s2n-quic bolero corpus-per-test pattern — https://github.com/aws/s2n-quic
+- yamux allocation guard / libp2p validate-without-allocating —
+  https://github.com/libp2p/rust-yamux ·
+  https://github.com/libp2p/rust-libp2p (gossipsub `validate_rpc_limits`)
+- rust-fuzz trophy case (finding-class taxonomy) — https://github.com/rust-fuzz/trophy-case
+- OSS-Fuzz Rust integration — https://google.github.io/oss-fuzz/getting-started/new-project-guide/rust-lang/
+- Scheduled CI fuzzing with cached corpora — https://depot.dev/blog/distributed-rust-fuzzing
+
+Internal: ADR-014 (envelope framing), ADR-034 (chunk header), ADR-040
+(backpressure/limits), ADR-042 (hub relay), ADR-031 (crate
+decomposition); review 006 E-04 (early-arrival cap sizing note,
+`src/channels/manager.rs:106-121`).
@@ -0,0 +1,561 @@
+# Review 006 — Channel-Open Establishment Gap (from alktunnels Phase 0)
+
+## Status
+
+**Resolved-by-ADR (E-01, N-1) / Implemented (E-02, E-03, E-04, N-2).**
+Findings filed from the alktunnels Phase 0
+research pass (2026-09-06). This is a design review, not a code-defect
+review: the establishment gap (E-01) is real, POC-observable, and
+load-bearing for the next downstream crate; the remaining findings are
+smaller mechanism/coverage gaps noticed in the same sweep.
+
+**2026-09-06 verification + remediation pass.** All four findings were
+independently re-verified against source at tree `88e3f5e` (0.4.1 +
+this review's own commit) — verdicts CONFIRMED for E-01..E-04, with
+one correction to E-02's cost estimate (see the verification appendix
+at the bottom of this file). Three additional findings filed from the
+same sweep: **N-1** (client error-type gap — blocking for E-01's
+consumer visibility), **N-2** (dead counter), **N-3** (panic posture,
+pinned). **E-01 + N-1 are resolved by ADR-049**
+(`docs/architecture/decisions/049-channel-open-establishment-phase.md`
+— split-hook `OpenEstablisher`, bounded await, `channel:open_failed`
+typed error). **Unit 1 (E-01 + N-1) is implemented** in alkcall 0.5.0
+(`OpenEstablisher` + `register_openable_with_establisher`, wrapper
+establishment phase with bounded await, `channel:open_failed` typed
+error, `ChannelOpenError` typed client error — all four verification
+gates landed as tests; two implementation-shape notes recorded in
+ADR-049's amendment: the establisher does not receive the channel
+`Connection` (yield-once BiStream belongs to the pump handler), and
+the bound is the earlier of dispatch deadline and per-registration
+timeout). **Unit 2 (E-02) is implemented** in alkcall 0.5.0
+(`OperationSpec.description: Option<String>` +
+`with_description`, `spec_to_json_pub` emits it when set,
+`rebuild_spec_for` parses it (shared by `from_call` and `op/register`),
+`services/list` and `services/list-peers` local listings emit it when
+set; the ADR-047 §6 amendment below records the discovery decision).
+**Unit 3 (E-03, E-04, N-2) is implemented** in alkcall 0.5.0 (E-03: the
+wrapper's handler-exit teardown discards `UnknownChannel` through a
+debug log + a benign-race pinning comment; E-04: the 64-parked-chunks
+observable bound is documented consumer-side in `channel-client.md` §
+"The early-arrival park bound (push-first producers)" and on the
+`EARLY_ARRIVAL_CAP` const; N-2: `early_arrival_count` is exposed via
+`ChannelManager::early_arrival_count()` — the observability choice,
+paired with `dropped_unknown_chunks` — with a monotonicity test).
+The original remediation sketch below is superseded by the
+"Remediation plan (post-verification)" section; the original sketch
+is retained for the record.
+
+Findings continue the review numbering with prefix `E` (001–005 used
+P/C/R/A/B/C/D/F/G — each review numbers independently).
+
+## Scope
+
+The channels open-op path (`run_open_wrapper` and the `OpenHandler`
+contract) reviewed from the perspective of the next consumer crate
+(alktunnels — arbitrary TCP/UDP tunnels over channels), cross-checked
+against the two existing consumers (alktty, alkhttp) and the SSH
+forwarding prior art recorded in
+`/workspace/@alkdev/alktunnels/docs/research/ssh-socks5-survey.md`.
+
+Everything below was verified directly in source at tree `a22b2b8`
+(0.4.1 + the early-arrival park fix). No code changes were made in
+this repo by this review. The 2026-09-06 re-verification pass
+(verification appendix) re-traced all findings at tree `88e3f5e` —
+no source changes touched the reviewed paths between the two trees
+(the only delta is this review's own commit).
+
+```
+Verified against: alkcall a22b2b8 (0.4.1); re-verified at 88e3f5e
+Reading list: src/channels/operations.rs (run_open_wrapper, OpenHandler,
+  make_open_handler_once/stream/sink), src/channels/manager.rs
+  (open_channel, teardown_channel, route_payload, early-arrival park),
+  src/channels/reassembly.rs (MpscSendStream::poll_shutdown, Drop,
+  MpscRecvStream::poll_read EOF arms), src/channels/mux.rs (implicit-EOF
+  pump path), src/protocol/wire.rs (CallError), src/registry/
+  registration.rs (invoke/invoke_streaming gates), src/registry/
+  discovery.rs (services/list, spec_to_json_pub), src/client/from_call.rs
+  (rebuild_spec_for), docs/architecture/decisions/047,
+  docs/architecture/channel-operations.md
+```
+
+## Severity legend
+
+Same scale as reviews 004/005:
+
+- **[critical]** — a decided spec invariant is violated in a way that
+  makes a promised capability unreachable end-to-end; or corrupts data.
+- **[major]** — a core protocol path cannot serve a decided behavior;
+  works only via shapes the spec does not describe.
+- **[minor]** — drift, doc/spec inconsistency, or a missing
+  convenience with no correctness impact.
+
+---
+
+# Part A — The open-op establishment gap
+
+## E-01 [major] — The open op cannot fail after allocation: the consumer receives a live channel for a tunnel whose establishment failed, with no error channel
+
+**Verified:** YES, by code trace and mechanism analysis.
+
+### The mechanics
+
+`OpenHandler` (ADR-047 §3) is the ALPN crate's hook for "validate
+params, consult ownership, prepare the backend" — i.e., the
+establishment phase of a channel. But the wrapper does not await it:
+
+1. `run_open_wrapper` (`src/channels/operations.rs:483-528`):
+   `policy.check_open` → `manager.open_channel(alpn, opener_id, None)`
+   → build the channel `Connection` → `open_handler(input, channel_conn,
+   auth)` **spawns** the handler and collects its `JoinHandle` →
+   `ResponseEnvelope::ok(request_id, json!({ "channel_id": channel_id }))`
+   (`operations.rs:503-527, 537`). The reply is written to the wire the
+   moment the handler task is *spawned*, not when the handler has done
+   its establishment work.
+2. The `OpenHandler` type (`operations.rs:333-334`) returns
+   `tokio::task::JoinHandle<()>` — there is no result, no error variant,
+   no establishment phase the wrapper can consult. Any failure inside
+   the handler (params valid at the schema level but semantically
+   rejected, backend lookup failure, target dial failure for a
+   `direct-tcpip`-shaped tunnel, resource no longer available) is
+   invisible to the open op's reply.
+3. What the consumer observes on handler-side failure: the call op
+   **succeeds** with `{channel_id}`, the channel is adopted
+   (`ChannelClient::open_channel`, `src/channels/client.rs:227-250`),
+   and then the channel EOFs — the handler wrote nothing before
+   exiting, the mux pump writes the implicit-EOF chunk on receiver end
+   (`src/channels/mux.rs:78-81`, REQ-CH-01 implicit-EOF path), and
+   `MpscRecvStream::poll_read` returns clean EOF for both the sentinel
+   and sender-drop arms (`src/channels/reassembly.rs:111-135`). A
+   dial-failure EOF is byte-for-byte indistinguishable from a target
+   that closed immediately after connecting — the two most different
+   failure/success stories map to the same consumer-visible event.
+
+### Why this is the wrong shape (SSH's semantics, prior-art checked)
+
+Every established tunnel/forwarding protocol puts establishment
+failure in the open reply, not in the data stream:
+
+- **SSH** (RFC 4254 §5.1): `SSH_MSG_CHANNEL_OPEN_FAILURE` is a
+  first-class reply to the open, carrying a reason code
+  (`ADMINISTRATIVELY_PROHIBITED` / `CONNECT_FAILED` /
+  `UNKNOWN_CHANNEL_TYPE` / `RESOURCE_SHORTAGE`) plus a description
+  string; the channel never exists on the opener's side afterward
+  (verified end-to-end in russh:
+  `src/server/encrypted.rs:1244-1278`, `src/client/encrypted.rs:414-434`
+  — see `/workspace/@alkdev/alktunnels/docs/research/ssh-socks5-survey.md`
+  §"Open-failure path").
+- **SOCKS5** (RFC 1928 §6): the reply carries REP codes 0x01–0x08 and
+  the connection closes within 10s on failure — error-then-close, never
+  "success then in-stream error."
+- **udpgw** (`tun2proxy/src/udpgw.rs:21-26`) is the counterexample: an
+  opaque ERR bit with zero reason information — the survey flags it as
+  the vocabulary to avoid.
+- **alktty was forced to reinvent the missing mechanism in-band.** The
+  direct-ALPN path answers the negotiation with a length-prefixed JSON
+  error frame *on the stream* (`send_negotiation_error`,
+  `alktty/src/adapter.rs:177-187`; the `0x00`-prefix first-byte
+  disambiguation trick, `alktty/docs/architecture/tty-adapter.md:186-197`),
+  and the channels path retains the same error-frame shape even though
+  the open op's `input` is the negotiation (alktty ADR-009) — because
+  post-allocation failures have nowhere better to go. That is
+  per-crate reinvention of a protocol-level capability every ALPN
+  crate will need: a structured, typed, **establishment-failure reply
+  to the open op**.
+
+### The cost today, concretely
+
+- A consumer cannot distinguish "ACL denied" (call error,
+  `channel:forbidden` — never allocated) from "dial refused" (open
+  succeeded, instant EOF) from "target accepted then instantly closed"
+  (open succeeded, instant EOF). Retry policy, client UX, and error
+  reporting are impossible on the second and third.
+- ADR-016's typed error details (`CallError.details`) — which the
+  wrapper already uses for `channel:too_many_channels` with
+  `{count, max}` details (`operations.rs:530-545`) — cannot carry
+  dial-failure reasons.
+- The alktty in-band error-frame path exists *only* because the
+  wrapper can't fail the open post-allocation; every future ALPN crate
+  faces the same fork: reinvent an in-band error vocabulary or
+  silently-EOF.
+
+### The ask (proposed shape, for the ADR — not a prescriptive API)
+
+Give the open-op wrapper an **establishment phase it awaits before
+replying**. Minimal, backward-compatible shape:
+
+1. `OpenHandler` gains an establishment result. Two candidate shapes:
+   - **Split the hook**: `OpenEstablisher` (async, awaited by the
+     wrapper — validates params semantically, prepares/dials the
+     backend, returns `Result<Establishment, EstablishmentError>`)
+     followed by `OpenHandler` (spawned on the established channel, as
+     today). The dial is the natural establisher step for tunnels; the
+     pumps remain the spawned handler.
+   - **Await-and-inspect**: keep the single `OpenHandler` returning
+     `JoinHandle<OpenResult>`; the wrapper awaits a bounded
+     establishment phase (a `JoinHandle::timeout` equivalent — select
+     on the handle vs an establishment deadline) before replying. The
+     handler signals "established, continue" via an agreed value
+     (e.g. the handler resolves a first `Result<(), HandlerError>`
+     promptly, or the wrapper watches a oneshot the handler signals).
+2. On establishment failure: the wrapper tears down the just-allocated
+   channel (`teardown_channel` — the ledger/policy paths already
+   handle this atomically) and replies with a **new typed CallError**,
+   e.g. `channel:open_failed`, with `details` carrying a reason code +
+   message. Reason-code vocabulary per the SSH four (the survey's
+   finding): policy-denied (already distinct — `channel:forbidden`),
+   dial-failed, unknown-resource-or-substrate, resource-shortage —
+   mapping 1:1 onto what an open handler can actually produce. Wire
+   addition is additive (new error code string + optional details
+   shape), no existing consumer breaks.
+3. Backward compatibility: the existing `OpenHandler` signature is
+   preserved if the split shape is chosen (old handlers still compile —
+   the establisher is a new, separately-registered hook, defaulting to
+   an always-OK establisher for the no-establishment-work case).
+
+### Alternative considered and rejected
+
+An in-band establishment/error frame (alktty-style, on the channel
+stream, alktunnels' original OQ-TN-09 direction) works without an
+upstream change, but: (a) it forces every ALPN crate to define a frame
+vocabulary and a disambiguation scheme (alktty's `0x00` peek is
+exactly this cost, paid once per crate); (b) it cannot carry typed
+`CallError.details` or participate in ADR-016 error schemas; (c) it
+leaves the phantom-opened channel in the manager (allocation/ledger/
+policy all fire for a channel that never carried data); (d) SSH's
+semantics — the failure is the open's reply, the channel never exists
+opener-side — are the cleaner contract, and channels is at exactly the
+maturity point (three downstream dependents, alkcall 0.4.x) to fix it
+upstream cheaply.
+
+### Severity
+
+[major] — not [critical]: no data corruption, and the capability is
+reachable via per-crate workarounds (alktty proves it). But it is the
+shape every future protocol crate will fight, the fix is cheaper now
+than after the next consumer, and the workaround path (in-band frames)
+bakes in a wire format that would then need to stay stable per crate.
+
+---
+
+# Part B — Smaller findings from the same sweep
+
+## E-02 [minor] — `services/list` discloses no per-op metadata; openable resources are indistinguishable by name alone
+
+`services_list_handler` (`src/registry/discovery.rs:247-269`) maps
+`list_operations()` to `{name, namespace, op_type}` only. For a tunnel
+registry, the consumer's discovery question is "which tunnel resources
+may I open" — and the answer arrives as a bare list of op names
+(`channels/tunnel/sub`...). Per-resource identity (which target, which
+substrate, human description) has no field to live in:
+
+- `services/schema` (`spec_to_json_pub`, `discovery.rs:211-236`) can
+  disclose it *per op* (input schema, access_control), so the data
+  path exists — but it is N+1 round-trips, and the input schema
+  describes the *open params contract*, not the *set of produced
+  resources* (a tunnel producer registers one op and N resources).
+- ADR-047 §6 already anticipated the dynamic half:
+  `channel/resources/subscribe` aggregates per-ALPN resource
+  enumerators — but the handler is a not-implemented stub
+  (`channel:resources_not_implemented`, OQ-40,
+  `operations.rs:274-299`).
+
+This is not an alkcall defect — OQ-40 is decided-deferred and the stub
+fails loudly by design. Filing it because alktunnels' discovery need
+(OQ-TN-08 resolution: "the ops listing IS tunnel-resource discovery")
+makes OQ-40 load-bearing for the first time: a consumer UI cannot
+distinguish produced tunnel resources without either the enumerator
+aggregation or a listing enrichment. Recommend deciding (small ADR or
+OQ-40 update) whether:
+
+1. `channel/resources/subscribe` lands (per-ALPN enumerators — the
+   decided shape), or
+2. `services/list` gains an additive per-op `description`/`metadata`
+   field (static, registry-side — cheap, but describes the op, not the
+   resource set), or
+3. Both: subscribe for live resource sets, list enriched for op
+   descriptions.
+
+alktunnels Phase 1 can proceed with (3)'s shape assumed; the minimal
+v1 consumer can also just know the op name out-of-band (config), which
+is why this is [minor] today.
+
+## E-03 [minor] — `OpenHandler`-exit teardown races `channel/close`'s awaited teardown, but the ledger `take` makes it benign (verify + document)
+
+`run_open_wrapper`'s spawned teardown task (`operations.rs:505-518`)
+and the `channel/close` handler's teardown path
+(`make_close_handler`, `operations.rs:170-238` — 5s await on the
+handler task, then ledger `take` + `on_close`) both walk
+`opener_ledger().take(id)` → `policy.on_close(opener)`. The `take` is
+atomic (first caller removes the entry), so no double-decrement — the
+cap cannot drift upward. But the loser of the race:
+- The wrapper task's `teardown_channel(id)` returns
+  `Err(UnknownChannel)` (logged? no — `let _ =` discard,
+  `operations.rs:509`) and skips the ledger/policy half silently.
+- The close handler's `Ok(task)` arm then awaits a task that is
+  already exiting.
+
+Verified benign for the cap invariant (`take` is the gate —
+`operations.rs:510`, `operations.rs:210`), but the `let _ =` discard
+at `operations.rs:509` means a real `UnknownChannel` after a
+`set_handler_task` failure (`operations.rs:520-527` — the "channel
+vanished between open and handler-task install" warn) is
+indistinguishable from a benign race. Recommend either a debug log on
+the discard or a comment pinning the race as designed. No correctness
+impact; filing for the record since it was checked during the E-01
+trace.
+
+## E-04 [minor] — Early-arrival park cap (64) interacts with push-first producers under slow adopters — cap-drop is silent at the consumer
+
+The early-arrival buffer (`EARLY_ARRIVAL_CAP = 64`,
+`manager.rs:111`, `park_early_arrival` `manager.rs:440-462`) is
+per-channel and drops past the cap with a debug log + counter —
+correct per the adopt-race design. But for a *tunnel* producer whose
+handler dials then immediately pumps (the common case), 64 chunks can
+arrive before the consumer's `adopt_channel` runs if the open-op
+response is delayed (relay hops, scheduling). The drops are counted
+(`dropped_unknown_chunks`) but not visible to the channel's
+consumer — data loss presents as a truncated stream with clean framing
+elsewhere. Not a correctness bug (the cap is the documented behavior;
+the fix shipped in `a22b2b8` is the right shape), but worth a note in
+the tunnel-crate's POC checklist: the UDP POC's MTU-vs-buffer sizing
+should treat 64 parked chunks as the observable bound. No alkcall
+change requested; filed so the constraint is visible to the next
+consumer.
+
+## Non-findings (verified correct, recorded to bound the re-review)
+
+- **The open-op ACL path is complete**: `invoke_streaming` runs the
+  same visibility + `AccessControl::check` + `input_schema` gates as
+  `invoke` (`registration.rs:380-404` vs `:347+`); the Sub-typed open
+  op's ACL failure is a `call.error` on the open, no channel
+  allocated. Verified against the `invoke_streaming_acl_denied_yields_
+  forbidden` test (`registration.rs:1628`).
+- **`input_schema` enforcement covers open params** (0.4.0, the
+  alktty-review-L1 fix): `check_input_schema` runs before the handler
+  in all three dispatch entry points; schema-invalid open params are
+  `INVALID_INPUT` call errors — never a phantom channel. The
+  semantic-beyond-schema gap is E-01's subject and is properly
+  post-schema.
+- **EOF arms are unified and clean**: both the sentinel (`Bytes::new`)
+  and sender-drop arms of `MpscRecvStream::poll_read` yield clean EOF
+  (`reassembly.rs:111-135`); the mux pump writes the implicit-EOF
+  chunk for handler-drop-without-shutdown (`mux.rs:78-81` +
+  `mux_pump_writes_eof_on_implicit_close` test). The two-pump
+  shutdown contract (alknet ADR-078) has its upstream half in place.
+- **The `channel_open` marker survives the wire round-trip**
+  (`spec_to_json_pub` emits the boolean; `rebuild_spec_for` re-derives
+  the ALPN from the op name — `from_call.rs:265-280`, `:298-314`),
+  including the `custom/proto` multi-segment case. The G-04
+  `resource_id_path` fix is present (`from_call.rs:260`,
+  round-trip test `from_call.rs:610-617`).
+- **The opener-ledger cap decrement is atomic with removal**
+  (`opener_ledger().take` gates every `on_close` path); the
+  double-decrement concern from ADR-047 §7 is closed at every call
+  site traced.
+
+---
+
+# Remediation sketch (original, superseded — see "Remediation plan (post-verification)")
+
+**Unit 1 — E-01 (the establishment phase).** Decided-shape ADR first
+(this is ADR-047 §3 contract territory — the `OpenHandler` type shape
+is a cross-crate API surface, and both existing consumers' handlers
+must be considered; alktty's `TtyOpenHandler` is the migration
+prototype). Implementation sketch: `ChannelCore::register_openable`
+gains an optional establisher hook; `run_open_wrapper` awaits it
+bounded (establishment deadline — a constant, e.g. 10s, or per-spec),
+tears down on failure, replies `channel:open_failed` with
+`{reason, message}` details on failure and `{channel_id}` on success.
+alktty migrates its channels-path error-frame to the call-error path
+where applicable (its direct-ALPN path keeps the in-band frame — two
+transports, two contracts). alkhttp unaffected (no openable ops).
+
+**Unit 2 — E-02 (discovery enrichment).** Decide via OQ-40 update +
+small ADR amendment: recommend (3) — subscribe for live resource sets
+(the decided shape, now load-bearing), plus an additive
+`description` field on the listing (cheap, immediately useful).
+**Implemented 2026-09-06 (alkcall 0.5.0):** the listing half landed
+(`OperationSpec.description`, four touchpoints as the appendix
+corrected); the subscribe half stays deferred (OQ-40, now with the
+load-bearing note).
+
+**Unit 3 — E-03/E-04.** E-03: log-or-comment; E-04: doc note. Trivial.
+
+# Remediation plan (post-verification)
+
+Firm ordering, decided 2026-09-06. E-01's ADR is **ADR-049**
+(`docs/architecture/decisions/049-channel-open-establishment-phase.md`)
+— decided shape: the **split hook** (`OpenEstablisher` awaited bounded
+by the wrapper, `OpenHandler` spawned unchanged after success), chosen
+over await-and-inspect because it preserves the `OpenHandler` type
+(backward compatible by construction), keeps establishment and pump
+lifecycles separate (SSH semantics: the dial is synchronous with the
+open reply), and restores ADR-047 §3's original "channel plan" wrapper
+shape. N-1 rides the same unit — without the client error-type fix,
+`channel:open_failed`'s typed reason is unreachable through the
+primary client path.
+
+**Unit 1 — E-01 + N-1 (alkcall 0.5.0).** `OpenEstablisher` +
+`register_openable_with_establisher` (no-establisher = always-OK,
+existing registrations compile unchanged); wrapper flow: `check_open`
+→ `open_channel` → await establisher bounded (dispatch deadline when
+`Some`, else `ESTABLISHMENT_TIMEOUT` = 10s) → on failure:
+`teardown_channel` + ledger `take` + `policy.on_close` + reply
+`channel:open_failed` with `details: {reason, message}` (reason ∈
+`dial_failed` / `unknown_resource` / `resource_shortage` /
+`handler_error` / `timeout`); on success: spawn pumps,
+`set_handler_task`, reply `{channel_id}`. `ChannelClient::open_channel`
+returns a typed error carrying the `CallError`. Concurrency is safe:
+the dispatcher spawns Once invocations as independent tasks
+(`dispatch.rs` `spawn_once_dispatch`), so an awaited establisher does
+not head-of-line-block channel 0. Version 0.5.0 (the `open_channel`
+error-type change is semver-relevant). **Status: IMPLEMENTED
+(2026-09-06)** — with two implementation-shape notes recorded in
+ADR-049's amendment: the establisher takes `(input, auth)` only (the
+yield-once channel `BiStream` belongs exclusively to the pump
+handler), and the effective bound is `min(dispatch deadline,
+registration timeout | ESTABLISHMENT_TIMEOUT)`. All four verification
+gates below are tests in the crate.
+
+**Unit 2 — E-02 (ride the 0.5.0 release).** Additive
+`description: Option<String>` on `OperationSpec` — note this is four
+touchpoints, not one (see the verification appendix's E-02
+correction): struct field + `spec_to_json_pub` emit +
+`rebuild_spec_for` parse + the `services/list` output-schema doc.
+`services/list` emits it when set. OQ-40 stays deferred but gains a
+"load-bearing for alktunnels discovery UI" note; the
+`channel/resources/subscribe` half stays deferred (alktunnels v1 uses
+config-known op names). **Status: IMPLEMENTED (2026-09-06)** — the
+discovery decision (3: enriched listing now, subscribe deferred) is
+recorded as an amendment to ADR-047 §6.
+
+**Unit 3 — E-03/E-04/N-2 (trivial batch, same PR series as Unit 1).**
+E-03: debug log (or pinning comment) on the discarded `UnknownChannel`
+at the wrapper's teardown discard. E-04: doc note on `EARLY_ARRIVAL_CAP`
+(the 64-parked-chunks observable bound) for tunnel-crate-facing
+consumers. N-2: expose an accessor for `early_arrival_count` or remove
+the write-only counter. **Status: IMPLEMENTED (2026-09-06)** — E-03:
+debug log + benign-race pinning comment on the wrapper's handler-exit
+teardown (mirroring the sibling log the Unit 1 establisher-failure
+teardown already carries); E-04: consumer-side doc note in
+`channel-client.md` plus the const doc; N-2: accessor
+(`ChannelManager::early_arrival_count()`, documented as monotonic —
+adopt-drain does not decrement) + test.
+
+**Sequencing:** ADR-049 (landed) → alkcall 0.5.0 (Units 1+2+3) →
+alktty migration (channels-path semantic failures move into an
+establisher; the direct-ALPN in-band error frame is retained — two
+transports, two contracts) → alkhttp mechanical pass
+(`OpenableAlpn.establisher: Option<...>`, default `None`). alktunnels
+Phase 1 blocks only on the ADR decision (landed), not the
+implementation: its OQ-TN-09 direction ("self-contained control frame")
+shrinks to *post-establishment* control only once `channel:open_failed`
+exists.
+
+## Verification gates for the E-01 remediation
+
+- A channels end-to-end test: producer handler whose establisher fails
+  after channel allocation → consumer's `open_channel` resolves
+  `Err` with `channel:open_failed` + reason details; no channel in the
+  manager's `channel_ids()` afterward (the SSH "channel never exists
+  opener-side" property, consumer-visible as "no `channel_id` was
+  ever returned").
+- A bounded-establishment test: establisher that never completes →
+  open op fails with a timeout-flavored error within the deadline,
+  channel torn down, ledger decremented.
+- An alktty-migration test: the existing
+  `open_via_channels_surfaces_negotiation_rejected` scenario resolves
+  via call error (or retained error-frame — per the ADR's chosen
+  compat shape) unchanged in behavior.
+- (Added post-verification) A compat gate: a no-establisher
+  registration behaves exactly as today — `{channel_id}` reply,
+  handler spawned, teardown on handler exit.
+
+## Verification appendix (2026-09-06 re-verification pass)
+
+All findings re-verified by independent source trace at tree `88e3f5e`.
+Verdicts, corrections, and the additional findings:
+
+- **E-01 CONFIRMED — and strengthened.** The wrapper's
+  spawn-then-reply flow is as described
+  (`src/channels/operations.rs` `run_open_wrapper`: handler spawned,
+  reply written before the handler performs any work). New supporting
+  evidence the original pass missed: **ADR-047 §3's decision text**
+  describes the ALPN open handler as "validate params, consult
+  ownership, prepare the backend, return a 'channel plan'" — an
+  awaited preparation the wrapper consults before replying. The
+  implemented `OpenHandler` (`JoinHandle<()>`) collapsed that phase
+  into a fire-and-forget spawn. E-01 is therefore **drift from
+  ADR-047 §3's own wrapper shape**, not merely a missing convenience —
+  the remediation restores the decided design, which lowers the ADR's
+  contention cost. Also verified: the serving loop spawns Once
+  invocations as independent tasks, so an awaited establishment phase
+  does not head-of-line-block other calls on channel 0 (a fix-feasibility
+  question the original pass did not address).
+- **E-02 CONFIRMED — one correction.** `services_list_handler` emits
+  `{name, namespace, op_type}` only, as described. But the "cheap,
+  additive `description` field" framing understates the work:
+  `OperationSpec` has **no `description` field at all** (the
+  `description` in `spec.rs` is on `ErrorDefinition`). The change is
+  four touchpoints: struct field, `spec_to_json_pub` emit,
+  `rebuild_spec_for` parse, and the `services/list` output-schema doc.
+  Still small; still [minor].
+- **E-03 CONFIRMED.** Both teardown paths gate on the atomic
+  `opener_ledger().take(id)`; the race loser gets `UnknownChannel` /
+  `take → None` — no double-decrement. The `let _ =` discard on the
+  wrapper's `teardown_channel` result is as described. Also traced:
+  the `set_handler_task` failure path still runs the wrapper task to
+  completion (self-teardown), so no leak in that arm either. The
+  log-or-comment remedy stands.
+- **E-04 CONFIRMED.** `EARLY_ARRIVAL_CAP = 64`, per-channel, FIFO,
+  drop-past-cap with debug log + `dropped_unknown_chunks` counter.
+  Doc-note-only remedy stands.
+- **N-1 [minor today, blocking for E-01's consumer visibility] —
+  `ChannelClient::open_channel` erases the typed error.**
+  (`src/channels/client.rs`) It flattens the `CallError` into a
+  `String` via `format!("open op failed: {e:?}")`. Even once the
+  wrapper replies `channel:open_failed` with reason details, a
+  consumer cannot branch on the reason — the error type destroys it.
+  E-01's verification gate ("consumer's `open_channel` resolves `Err`
+  with `channel:open_failed` + reason details") is unreachable without
+  changing this error type, so the fix is in scope for the E-01 unit
+  (ADR-049 §4), not deferred.
+- **N-2 [trivial] — `early_arrival_count` is write-only.** Incremented
+  in `park_early_arrival`, never read anywhere (no accessor; only
+  `dropped_unknown_chunks` is exposed). Either expose an accessor
+  (observability for the E-04 bound) or remove the counter.
+- **N-3 [observation, pinned by ADR-049 §6] — panicked pump handlers
+  are EOF-shaped by design.** The wrapper's teardown task swallows the
+  pump handler's `JoinError` (`let _ = raw_task.await`). A panicked
+  handler = phantom channel + instant EOF, indistinguishable from a
+  clean short-lived channel. With the establisher split, the pump-phase
+  panic stays in this category (correct — there is no mid-stream error
+  channel by design; establishment errors are the only kind that
+  belong in the open reply). ADR-049 §6 pins this posture; no change.
+
+## References
+
+- alknet ADR-078 / channels two-pump contract — the teardown half this
+  review's EOF-arms non-finding confirms upstream.
+- alkcall ADR-047 (openable ALPNs are operations), ADR-016 (typed
+  error schemas — the vehicle for `channel:open_failed` details),
+  ADR-040/041 (backpressure/caps — untouched by E-01).
+- alktty ADR-009 (the open op's input is the negotiation) + review
+  #001 L1/L3 resolution — the per-crate workaround E-01 obsoletes;
+  `send_negotiation_error` (`alktty/src/adapter.rs:177-187`) and the
+  `0x00`-peek (`alktty/docs/architecture/tty-adapter.md:186-197`) are
+  the in-band mechanism the upstream establisher replaces for the
+  channels path.
+- alktunnels Phase 0 (`docs/research/phase-0-findings.md` OQ-TN-09)
+  and the SSH/SOCKS5 survey (`docs/research/ssh-socks5-survey.md`
+  §"Open-failure path", §"Comparison") — the prior art motivating
+  E-01's reason-code vocabulary.
+- The consumer-findings ledger convention (`docs/reviews/consumer-
+  findings-ledger.md`) — findings here follow the same spirit
+  (downstream-discovered, filed for upstream action); E-01..E-04 are
+  alktunnels-discovered but numbered in alkcall's review series since
+  they are alkcall findings.
+- **ADR-049** (`docs/architecture/decisions/049-channel-open-
+  establishment-phase.md`) — the E-01/N-1 resolution (split-hook
+  `OpenEstablisher`, bounded establishment, `channel:open_failed`
+  typed error, client error-type fix).
@@ -0,0 +1,343 @@
+# Review 007 — Establishment Follow-Ups (from the alktunnels UDP POC)
+
+## Status
+
+Resolved — all three units landed in alkcall 0.6.0 (2026-09-07):
+Unit 1 `dc4ad2b` (R-01 + R-02's doc notes), Unit 2 `8f122b0` (R-02's
+telemetry), Unit 3 `9c6fec1` (R-03 + ADR-050). Two deviations from
+the sketches below, both recorded in the ADRs: (1) R-01's plan is
+**typed-opaque** (`ChannelPlan = Arc<dyn Any + Send + Sync>`), not
+`Option<Value>` — the sketch could not satisfy this review's own
+verification gate, because the payloads establishers hand off are
+live handles (dialed sockets, TTY handles) with no JSON
+representation; (2) R-03's helper returns `(u64, u64)`, not
+`io::Result<(u64, u64)>` — both pumps swallow copy errors by the
+ADR-078 contract (mid-stream error = abrupt close), so an `Err` state
+would be dead code. Original findings below, retained as filed
+(verified against tree `36e74cd`, 0.5.0).
+
+Open — findings filed from the alktunnels UDP POC pass
+(`alktunnels-udp-poc`, 2026-09-06; summary at
+`/workspace/@alkdev/alktunnels/docs/research/poc-summary.md`). This
+review exists to prevent a second fix→publish→update-dependents cycle:
+every finding below is either (a) guaranteed to be needed by
+alktunnels Phase 1 implementation, or (b) a documented contract gap
+that will bite the next `OpenHandler` author the way it bit the POC.
+Nothing here is speculative — each finding was reached by writing
+working code against 0.5.0 and finding the shape insufficient.
+
+Findings continue the review numbering with prefix `R` (001–006 used
+P/C/R/A/B/C/D/F/G/E — each review numbers independently).
+
+> **Post-remediation note (2026-09-07):** the "Open —" paragraph
+> above is the original filing state, retained for the record. All
+> units landed; see Status above and ADR-049 amendment 2 + ADR-050.
+
+## Scope
+
+The ADR-049 establishment surface (`OpenEstablisher`, `Establishment`,
+`EstablishmentError`, `register_openable_with_establisher`) and the
+`OpenHandler` contract, reviewed from the alktunnels UDP POC's
+consumer/producer implementations. Everything verified against source
+at tree `36e74cd` (0.5.0). Cross-references: alkcall review 006
+(E-01..E-04), alkcall ADR-049, alktunnels `poc-summary.md`
+(§Issues Surfaced), alktty's channels establisher
+(`make_tty_establisher`).
+
+```
+Verified against: alkcall 36e74cd (0.5.0)
+Reading list: src/channels/operations.rs (OpenEstablisher, Establishment,
+  run_open_wrapper, teardown_failed_channel), src/channels/client.rs
+  (ChannelOpenError::establishment_reason), src/channels/manager.rs
+  (teardown_channel, adopt_channel), docs/architecture/decisions/
+  047 + 049, and the consumers: alktty src/channels.rs (make_tty_
+  establisher / make_tty_open_handler), alkhttp src/websocket/
+  upgrade.rs (OpenableAlpn ferry), alktunnels-udp-poc src/producer.rs
+```
+
+## Severity legend
+
+Same scale as reviews 004–006.
+
+---
+
+# Part A — The findings
+
+## R-01 [major] — `Establishment` is payloadless, but the channel plan is exactly what establishers need to hand to the pump handler
+
+**Verified:** YES — by building against the API. The ADR-049 §1 text
+itself anticipates this: *"Reserved for a channel plan — today the
+wrapper consults only success/failure, so `()` carries no data"*
+(`src/channels/operations.rs:341-345`, the empty
+`pub struct Establishment {}`).
+
+### The mechanism
+
+The establisher is pre-data-plane: it cannot see the channel's
+yield-once `BiStream` (ADR-049 amendment), so anything it
+establishes — a dialed socket, an allocated handle — must cross to
+the pump handler through a side channel the ALPN crate invents. The
+alktunnels POC's workaround is a resource-keyed
+`Mutex<HashMap<String, SubstrateHandle>>` + a poll-loop `take`
+(`producer.rs::HandleHandoff`) that works only because the wrapper
+guarantees establisher-before-handler ordering. The costs:
+
+1. **Concurrent same-resource opens race the slot.** Two opens of the
+   same resource: the second establisher's `deliver` overwrites the
+   first handler's not-yet-taken handle. The POC documents this as a
+   simplification; a real crate cannot.
+2. **alktty hit the same wall and documented it as a limitation.**
+   `alktty/src/channels.rs:253-257`: the establisher cannot carry the
+   allocated `TtyHandle` across, so *backend allocation* stays
+   post-open in the pump handler (`allocate_failed` remains an
+   in-band negotiation error frame — ADR-010) — exactly the
+   phantom-channel-ish shape ADR-049 exists to eliminate, still
+   alive one layer down. TTY's establisher can only validate/lookup/
+   ownership-check; the one thing that can actually fail with a
+   runtime error (allocate) is unreachable from the typed error path.
+3. **Every ALPN crate pays the side-channel tax again.** Handoffs,
+   slots, poll loops or oneshots — per crate, per resource key, all
+   with the same concurrency caveat.
+
+### The ask
+
+Give `Establishment` its payload — the channel plan ADR-047 §3
+originally described ("return a 'channel plan'... the wrapper consults
+its result"). Minimal shape:
+
+```rust
+pub struct Establishment {
+    /// ALPN-defined plan data — the dialed handle, an allocation
+    /// ticket, whatever the pump phase needs. Opaque to alkcall.
+    pub plan: Option<Value>,
+}
+```
+
+or, keeping it typed at the boundary:
+
+```rust
+pub struct Establishment { pub plan: Option<Value> }
+```
+
+with the wrapper passing `establishment.plan` (or `Null`) to the
+`OpenHandler`'s `input` — e.g. as a well-known key the pump handler
+reads, or as a third callback parameter. The wire surface is
+**unchanged** (the plan is process-local: establisher → wrapper →
+handler in the same process on the producing side; nothing crosses
+the transport that isn't already the open op's input). Consumers'
+`Ok(Establishment {})` construction sites (alktty has two; alkhttp's
+ferry has none) break mechanically at 0.6 — `Establishment::new(plan)`
+/ `Establishment::default()` make the migration one-liners.
+
+**The break is the point of doing this now:** 0.5.0 published
+yesterday with `Establishment {}` documented as reserved. The next
+consumer (alktunnels) needs the payload in Phase 1 — implementing
+Phase 1 without it means shipping the POC's side-channel handoff into
+the real crate, with its same-resource race, and then the payload
+lands later anyway as *another* breaking release. Filling the
+reserved field now is the cheap moment; the alternative is paying the
+breaking change twice.
+
+### Severity
+
+[major] — the capability gap is structural for any establisher whose
+backend produces a handle (tunnels: dial; TTY: allocate), not a
+polish item. Not [critical] because workarounds exist (the POC proves
+one), but every workaround carries the same-resource race or forces
+failure classes back into per-crate in-band frames — the exact cost
+ADR-049 was written to remove.
+
+---
+
+## R-02 [minor] — The `OpenHandler` `JoinHandle` lifetime contract is undocumented and load-bearing (found empirically by the POC)
+
+The POC's first pump implementation returned a wrapper task that
+spawned the pump as a nested fire-and-forget task. The result:
+**every tunnel connected then instantly EOF'd with zero bytes** — the
+wrapper awaited the (already-complete) handler task, tore the channel
+down at birth, and both pumps saw immediate EOF. Everything upstream
+(establisher, open reply, channel routing) looked healthy; the bug
+was purely in the handler's return-value semantics.
+
+The contract, as implemented: the wrapper awaits the returned
+`JoinHandle` and *that completion is the teardown trigger*
+(`run_open_wrapper`'s spawned task: `let _ = raw_task.await;`
+→ `teardown_channel(id)` → drop the demux sender → EOF to the
+handler's read half). Therefore:
+
+- **The returned `JoinHandle` must track the data-plane lifetime.** A
+  handler that returns before its pumps finish tears the channel down
+  at birth. The pump must be awaited *inline* inside the handler task
+  (`let _ = pump_halves(...).await;`), not spawned-and-forgotten.
+- Half-open semantics fall out of this correctly (one pump finishing
+  shuts down the opposite sink per ADR-078; the handler's task
+  completes when both pumps finish — which is when teardown *should*
+  happen). The contract is right; only its documentation is missing.
+
+The current type docs (`operations.rs:325-339`) say the handle is
+"recorded for teardown (abort on `channel/close` / connection drop)"
+— abort semantics — but never say **early return = teardown-at-birth**.
+alktty got this right by accident of shape (`drive_session_pre_negotiated`
+awaited inline in its single spawned task — `channels.rs:355-395`);
+the POC got it wrong the natural way. The next consumer will write
+the wrong shape too, because the natural reading of "spawn your
+protocol and return the `JoinHandle`" is a task-spawner, not a
+lifecycle promise.
+
+**The ask:** doc note on `OpenHandler` and
+`ChannelCore::register_openable*` — "the returned `JoinHandle` must
+track the data-plane lifetime: the wrapper awaits it and tears the
+channel down on completion; return a task that runs the handler to
+completion, never a spawner that exits early" — plus the ADR-049
+amendment (§1 or §6) recording the semantics. Optional hardening (not
+required): a `debug!` in `run_open_wrapper` when the awaited handler
+exits without the channel's `BiStream` having been accepted (a
+telemetry hint for the birth-teardown pattern; the accept is
+observable in-process). Doc-only; no break.
+
+---
+
+## R-03 [minor, optional unit] — The two-pump helper's convergence test is satisfied; extracting it now removes the last reason for a later sweep
+
+alknet ADR-078 deferred helper extraction until a second two-pump
+consumer existed and the shapes converged. The POC supplies both
+halves of that test:
+
+- **Producer side:** the alktunnels POC's `pump_halves` — two
+  `tokio::io::copy` pumps over split channel-vs-substrate halves,
+  each pump shutting down the opposite sink on completion, joined.
+- **Consumer side:** `TunnelSession::take_halves` + the assembly
+  layer's copy — the same shape modulo channel side.
+
+The shapes converged. The helper (`pump_bidi` or similar) is a
+candidate for **this same 0.6 sweep** — additive (a new pub fn in
+`channels` or `core`), zero breaking change, and it pins the
+ADR-078 contract in one place instead of three. The natural signature
+follows the POC:
+
+```rust
+pub async fn pump_bidi<A, B>(a: A, b: B) -> io::Result<(u64, u64)>
+where
+    A: AsyncRead + AsyncWriteExt + Send + Unpin,
+    B: AsyncRead + AsyncWriteExt + Send + Unpin,
+```
+
+(join'd two-pump with shutdown-on-completion; returns the copy
+counts for observability). alktty's three-pump session does not fit
+it (the exit future is a third signal) — that is fine; the helper
+serves the two-pump shape, TTY stays as-is.
+
+**The ask:** decide in this sweep — either extract in 0.6 (additive;
+recommended, since alktunnels Phase 1 will implement the pattern
+anyway and an upstream helper makes the third consumer free), or
+record the explicit decision to keep it per-crate. Do not leave it
+half-decided: an un-extracted helper is not itself a break, but
+finding this out during Phase 1 would be the same
+fix→publish→update treadmill for a purely additive change.
+
+---
+
+# Part B — Verified non-issues (bounded so the next review doesn't re-check)
+
+- **The reverse-flow (`-R`) story needs no upstream change.** A hub
+  proxy opening a channel *toward* a worker is the worker serving its
+  own open op on the connect side — supported by
+  `ChannelClient::from_connection_with_serving` (ADR-022 §2 both-sides
+  semantics) + `ChannelOperations::register_on` on the serving
+  registry + the wrapper allocating on the serving side (ADR-047 §5
+  "the side that holds the `ChannelManager` allocates" — both sides
+  do, with odd/even split per ADR-047 §5). Verified by trace; no API
+  gap. alktunnels' reverse-flow POC (OQ-TN-10 #2) will exercise this
+  end-to-end, but no upstream mechanism is missing.
+- **The establisher receives registry-validated input** —
+  `invoke_streaming`'s `input_schema` check runs before the wrapper
+  (`registration.rs:397`); the establisher's `input.clone()`
+  (`operations.rs:718`) is post-schema. Confirmed; no gap.
+- **Typed establishment errors are complete on the wire** —
+  `establishment_error_to_call_error` carries both `reason` and
+  `message` in `details` (`operations.rs:646-653`); the client-side
+  `establishment_reason()` branches on it (`client.rs:75-83`); alktty's
+  open spec declares the matching `ErrorDefinition` (ADR-016). The
+  vocabulary needs no extension for tunnels (`dial_failed` /
+  `unknown_resource` / `resource_shortage` / `handler_error` /
+  `timeout` cover every tunnel establisher failure class — verified by
+  the POC's three typed-error tests).
+- **The early-arrival park cap (64)** — reviewed in 006 E-04; the POC
+  treated it as a sizing constraint, not a defect. Unchanged.
+- **`EstablishmentError`'s reason set is sufficient** — the POC's
+  establisher used three of four reasons; `handler_error` covers
+  params-parse failures (the TTY pattern). No new reason needed.
+
+---
+
+# Remediation plan
+
+## Unit 1 — `Establishment` carries the channel plan (R-01)
+
+1. ADR-049 amendment (or ADR-050-adjacent amendment): `Establishment`
+   gains `plan: Option<Value>` (ALPN-opaque); the wrapper threads
+   `plan` into the pump handler (third `OpenHandler` parameter, or
+   merged into `input` under a reserved key — decide in the ADR; the
+   separate-parameter shape avoids colliding with the input schema).
+2. Bump to 0.6.0 (breaks `Ok(Establishment {})` construction sites —
+   alktty, two sites; mechanical `Establishment::default()` or
+   `Establishment { plan: None }`).
+3. Migration: alktty can then move backend `allocate` into its
+   establisher (killing the in-band `allocate_failed` frame on the
+   channels path — ADR-010's reason for that frame disappears);
+   alktunnels Phase 1 uses `plan` for the dialed handle; alkhttp's
+   ferry passes `Option` through unchanged.
+
+## Unit 2 — `OpenHandler` lifetime doc note (R-02)
+
+Doc-only (type docs + ADR-049 amendment). Optional debug warning.
+No break.
+
+## Unit 3 (optional) — `pump_bidi` helper extraction (R-03)
+
+Additive pub fn + tests. No break. Do it in the same 0.6 or record
+the decision not to.
+
+## What must NOT ride along
+
+Nothing else. The remaining alktunnels Phase 1 needs (UDP codec ADR,
+reverse-flow lifecycle, access-policy details) are alktunnels-local
+spec work — the POC validated the mechanics and found no further
+upstream gaps. The deliberate goal of this review: **0.6 is the last
+breaking sweep forced by known work**; anything after it should be a
+genuinely new discovery, not a known-dangling item.
+
+## Verification gates
+
+- Unit 1: end-to-end test — establisher dials, `plan` carries the
+  handle, pump handler receives it; concurrent same-resource opens
+  each get their own handle (the race the POC documented is
+  unreachable); alktty migration test (`allocate` in the establisher
+  → `allocate_failed` is a call error, no in-band frame).
+- Unit 2: doc gate only (`cargo doc` clean; the note present on both
+  the type and the registration entry points).
+- Unit 3: helper test — the POC's two-pump semantics (EOF from one
+  direction completes the other; shutdown-on-completion) reproduced
+  through the helper.
+
+## References
+
+- alkcall review 006 (E-01 establishment gap; R-01 is the payload
+  half of E-01's own remediation — ADR-047 §3's "channel plan"
+  through the reserved `Establishment` field) and ADR-049 (the
+  establishment phase; §1's original sketch already described the
+  plan-carrying shape).
+- alkcall ADR-047 §3 ("return a 'channel plan'" — the original shape
+  this review restores), ADR-022 §2 (both-sides serving — the
+  reverse-flow non-finding), ADR-047 §5 (odd/even allocation —
+  reverse-flow allocation on the serving side).
+- alknet ADR-078 (the two-pump contract; R-03's helper pins it
+  upstream).
+- alktunnels `docs/research/poc-summary.md` (§Issues Surfaced #1/#2 —
+  the empirical findings; §#4 — the convergence input for R-03) and
+  the POC crate (`/workspace/alktunnels-udp-poc`, 17 tests — the
+  empirical basis for every finding here).
+- alktty `src/channels.rs:253-257` — the existing documentation of
+  the R-01 cost on the TTY side (`allocate` cannot cross; in-band
+  `allocate_failed` remains), the second consumer confirming the gap
+  is not tunnel-specific.
@@ -0,0 +1,519 @@
+# Review 008 — Graduation Upstream Asks (from the alktunnels graduation)
+
+## Status
+
+Resolved — all three remediation units landed in alkcall 0.8.0
+(2026-09-18): Unit 1 `82ddddf` (U-2, ADR-049 amendment 3), Unit 2
+`620180d` (U-1, ADR-047 amendment 3), Unit 3a `90c1820` (the in-tree
+`ChannelRelay`, ADR-051), Unit 3b `4e52bd4` (the hub-leg install
+template, ADR-051 §5), Unit 3c (the gate-2 e2e harness in
+`src/channels/gate2_tests.rs` + the relay's producer-leg teardown +
+this release's bookkeeping). Two notes on the as-filed text: the U-2
+line citation is 945, not 955 (see Errata), and U-1's gate 2 landed as
+an in-tree relay component plus a permanent e2e gate rather than a
+test-only harness (the escalation the remediation plan pinned above).
+Original findings below, retained as filed (verified against tree
+`3b36b40`, 0.7.1).
+
+> **Errata (post-landing):** U-2 cites the reply construction at
+> `src/channels/operations.rs:955`; the cf-006/007 commit had already
+> shifted it to 945 by filing time. The citation in the finding below
+> is left as filed; the verified line is 945.
+
+Open — filed 2026-09-16 from the alktunnels graduation spec work
+(ADRs 007/008 at
+`/workspace/@alkdev/alktunnels/docs/architecture/decisions/`;
+research record at
+`/workspace/@alkdev/alktunnels/docs/research/tunnels-graduation.md`).
+Both asks are prerequisites for the alktunnels graduation
+implementation (the direct op + the listen-metadata shape), which is
+deliberately sequenced AFTER these land — alksocks (the first
+consumer) composes against the graduated surface, so the discovery
+and reply shapes must be final before it pins them. Verified against
+alkcall tree @ HEAD, 0.7.1 (all code references below cite current
+files/lines).
+
+Findings continue the review numbering with prefix `U`.
+
+## Scope
+
+The two wire-adjacent surfaces the graduation's ADRs depend on:
+(1) the open-op ↔ discovery relationship (alkcall ADR-047's op-name →
+ALPN derivation and its relay reconstruction), which flavor-form open
+op ids must survive; (2) the establishment → reply boundary
+(alkcall ADR-049's wrapper), which a bind-first listen establisher
+must be able to project metadata into. Both are additive; neither
+changes the channels data-plane wire format (ADR-034/071 untouched).
+
+## U-1: Flavor-form open-op ids in discovery derivation
+
+**Finding.** *(Resolved — ADR-047 amendment 3, Unit 2 `620180d`; the
+explicit `channel_open_alpn` field plus the last-segment derivation,
+exactly the pinned (b)+(c) shape. Gate 2 landed as the in-tree relay +
+`src/channels/gate2_tests.rs`, Unit 3.)* ADR-047 §1 pins the open-op
+naming to exactly two shapes
+per ALPN — `channels/<alpn>/sub` and `channels/<alpn>/pub` — and Gap
+F's marker derivation (`rebuild_spec_for`,
+`src/client/from_call.rs:209` + `derive_alpn_from_op_name`,
+`src/client/from_call.rs:305`) parses exactly those suffixes to
+reconstruct the `channel_open` marker after discovery
+(`spec_to_json` serializes the marker as a boolean,
+`src/registry/discovery.rs:244` — the ALPN string itself does not
+survive the round trip). alktunnels' graduation pins two NEW
+`Sub`-typed open ops on the existing `alk/tunnel` ALPN with
+flavor-form op ids:
+
+- `channels/tunnel/direct` (ADR-007 — dynamic-target egress; the
+  ssh `direct-tcpip` capability, scope `tunnel:direct`)
+- `channels/tunnel/forwarded` (ADR-008 — accept-as-open toward the
+  listen-opener side; the ssh `forwarded-tcpip` capability, scope
+  `tunnel:forwarded`)
+
+Runtime is NOT blocked today: registration sets the ALPN marker
+explicitly (`with_channel_open`), dispatch never parses the op name
+(`register_openable_with_establisher` accepts any spec name with a
+marker — verified, `src/channels/operations.rs:596`), and the client
+takes the ALPN as an argument (`open_channel(op_id, params, alpn)`).
+The gap is **discovery + hub relay**: a flavor-form op id fails
+`derive_alpn_from_op_name`'s suffix match, so `rebuild_spec_for`
+rebuilds the spec WITHOUT the `channel_open` marker, so a hub
+consuming through discovery (the `from_call` relay path, ADR-047 Gap
+C — the alknodes re-produce shape) treats the open op as a plain
+forwarding stub instead of wrapping it with relay machinery.
+
+**Prior art in-tree.** `derive_alpn_from_op_name` already tolerates
+multi-segment ALPNs (`segment.contains('/')` → used verbatim, so
+`channels/x-y/sub` → `alk/x-y`); the shape is one suffix away from
+flavor support.
+
+**Requested change.** Extend the op-name convention (ADR-047
+amendment): `channels/<alpn>/<flavor>` is a valid open-op name where
+`<flavor>` is a bare path segment (no `/`); the derivation generalizes
+from "strip `/sub` or `/pub`" to "strip the LAST segment when it is a
+known op-type marker (`sub`, `pub`) or a flavor registered with an
+explicit ALPN marker." Two viable implementation shapes, either
+acceptable:
+
+- **(a) Suffix-set extension** — `strip_suffix` against
+  `["/sub", "/pub"]` extended with a flavor allowlist threaded from
+  registration. Minimal, but couples discovery to a registry.
+- **(b) Wire the flavor op's ALPN explicitly through discovery** —
+  add an optional `channel_open_alpn` string field to the
+  `services/schema` payload (`spec_to_json` emits the ALPN string
+  instead of `true` when the op name is not a standard `…/sub`/`…/pub`
+  shape; `rebuild_spec_for` prefers the explicit string). This also
+  future-proofs the boolean-only marker (Gap F) whose round-trip is
+  lossy by construction for any non-derivable name.
+
+alktunnels ADR-002 Amendment 1 pins the convention sentence ("new
+flavors are new op ids — additive; the `…/sub` op is never reused for
+a different meaning"); alkcall's amendment should mirror it. The
+boolean marker's wire meaning for standard-shape ops is unchanged.
+
+**Why one-way-door timing:** the op ids are wire-stable from the
+first consumer (alksocks). If discovery's derivation ships after
+consumers exist, hubs deployed in between cannot relay the new ops —
+the failure is silent (plain forwarding stub instead of channel
+relay), which is the worst failure mode for a relay.
+
+**Verification gates:**
+
+1. `rebuild_spec_for("channels/tunnel/direct" summary)` reconstructs
+   the spec WITH `channel_open = alk/tunnel`.
+2. A hub-relay round trip over a real channels connection: consumer →
+   hub (`from_call` + relay wrapper) → producer, opening
+   `channels/tunnel/direct` end to end, the hub forwarding the
+   channel (the ADR-042 relay path riding the reconstructed marker).
+3. Old boolean-marker ops (`channels/tty/sub`) round-trip unchanged
+   (no regression on the existing derivation).
+
+## U-2: Establisher → reply projection (`Establishment` contributing reply fields)
+
+**Finding.** *(Resolved — ADR-049 amendment 3, Unit 1 `82ddddf`: the
+`reply_fields` carrier, the `channel_id` reservation failing loudly,
+`open_channel_with_reply` on the client.)* The open-op success reply
+is constructed by the wrapper
+and hardcoded to the channel id:
+`ResponseEnvelope::ok(request_id, json!({ "channel_id": channel_id }))`
+(`src/channels/operations.rs:955` in `run_open_wrapper`). ADR-049 §1
+explicitly reserved the establishment phase as the wire's pre-data
+moment and ADR-049 amendment 2 landed the typed-opaque plan
+(`Establishment { plan }`) for the establisher → handler direction —
+but the establisher has no path to contribute to the REPLY (the
+establisher → opener direction). alktunnels ADR-008's bind-first
+listen establisher needs exactly that: establishment ends at bind
+time, and the observed OS-chosen bound address must ride the open-op
+reply as an additive `"bound"` field (the SOCKS5 BIND reply#1
+`BND.ADDR` fidelity ask; the alternative — an out-of-band query op —
+is a new wire surface, strictly worse than an optional reply field).
+
+**Shape note.** `#[non_exhaustive]` on `Establishment`
+(ADR-049 amendment 2) anticipated exactly this carrier change. The
+sketch:
+
+- `Establishment` gains optional reply fields — e.g.
+  `Establishment::new(plan).with_reply_field("bound", json!({...}))`
+  or `reply_fields: Option<Map<String, Value>>` (bikeshed: builder
+  vs struct field; the map shape generalizes beyond `bound` without
+  a second amendment).
+- The wrapper merges them into the success output AFTER reserving
+  `channel_id` (wrapper-owned key: an establisher-provided
+  `channel_id` key is an establisher bug — reject or
+  `handler_error`-class it loudly rather than shadowing).
+- Absent fields → the reply is byte-identical to today's; no schema
+  change on the wrapper side (the output schema is the op's own
+  concern — alktunnels' listen-op spec documents `bound` as an
+  optional output field).
+
+**Consumer-compat check:** `open_channel` extracts `channel_id` from
+the response and ignores unknown fields (the client-side parse,
+`src/channels/client.rs:932`'s contract: "respond `{ channel_id }` —
+asserts the response carries a channel_id"), so old consumers are
+unaffected by a NEW field; new consumers reading `bound` against an
+OLD alkcall simply see the field absent — the additive posture
+alktunnels ADR-008 §2 pins ("until upstream lands, the field is
+simply absent").
+
+**Requested change (ADR-049 amendment 3):** the reply projection as
+sketched above, with the `channel_id` reservation documented.
+
+**Verification gates:**
+
+1. An establisher returning a reply field produces
+   `{ channel_id, bound }` on the wire; one returning none produces
+   `{ channel_id }` (byte-identical to today's).
+2. An establisher attempting to set `channel_id` fails loudly (the
+   reservation holds).
+3. The existing establishment tests (establisher-success pump
+   round-trip, no-establisher compat) pass unchanged.
+
+## Non-asks (recorded to bound the review)
+
+- **The channels data plane is untouched** — the forwarded op's data
+  plane is the existing `BiStream` + `pump_bidi`; the `bound` field
+  is call-plane JSON. ADR-034/071's one-way doors stay closed.
+- **No new alkcall op types** — both new tunnel ops are `Sub`-typed
+  open ops (the existing `HandlerKind::Stream` wrapper path).
+- **No identity/ACL changes** — the new scopes (`tunnel:direct`,
+  `tunnel:forwarded`) ride the existing op-spec `required_scopes`;
+  the per-call opener identity (CF-005/CF-006) is the only identity
+  surface the establisher/handler need (the forwarded op's `peer`
+  param is producer-asserted data, not transport truth — alkcall need
+  not validate it).
+
+## References
+
+- alktunnels ADR-007 (`docs/architecture/decisions/007-direct-open-op.md`),
+  ADR-008 (`008-listen-metadata-forwarded-op.md`) — the consumers of
+  both asks, with the full context and alternatives
+- alktunnels ADR-002 Amendment 1 — the flavor-form op-id convention
+  sentence
+- alkcall ADR-047 (open ops, Gap F, the derivation),
+  ADR-049 (establishment; amendment 2 — the plan payload whose
+  `#[non_exhaustive]` anticipates this carrier), ADR-042 (hub relay —
+  the relay path U-1's gate 2 exercises)
+- alksocks `poc-bind-findings.md` (the two fidelity asks with
+  evidence; the upstream-ask ledger this review retires)
+- Review 007 (the precedent for this filing: POC-driven upstream asks
+  before the dependent implementation)
+
+---
+
+# Remediation plan (adopted 2026-09-16 — findings verified, plan pinned)
+
+Both findings verified against HEAD `3b36b40` (0.7.1) — all code
+citations check out, with one line drift: U-2's reply construction is
+`src/channels/operations.rs:945` (review cites 955; the cf-006/007
+commit shifted the wrapper down ten lines). One review-scope deviation
+from the as-filed text, adopted in planning:
+
+- **U-1's gate 2 escalates from "test harness" to an in-tree relay
+  component.** The as-filed review treated ADR-042's relay wrapper as
+  consumer-side code (the ADR's §Scope note pins the implementation
+  downstream). The consumer decision is that the re-produce/relay shape
+  is general (alkhttp's fallback hub, alknodes, the vpn-like endgame all
+  compose it), and a real consumer now requires it — so ADR-042 is
+  amended: the relay implementation moves into alkcall as a reusable
+  component, and gate 2 becomes a genuine in-tree e2e.
+
+Design decisions pinned above the as-filed option lists:
+
+- **2026-09-17 (Unit 3 planning session): Unit 3 split into 3a/3b/3c
+  and design pinned in ADR-051** (`docs/architecture/decisions/
+  051-channel-relay-and-hub-leg.md`) — the session's discussion
+  expanded the unit's scope beyond the as-pinned sketch: the hub/spoke
+  family (hub or spoke may relay; the hub re-exposes spoke services by
+  ACL without binding ports) needs the call-half support too (the
+  hub-leg install template — now Unit 3b). Key decisions, all in
+  ADR-051: the relay holds `Arc<CallConnection>` + `ChannelManager`
+  per producer leg (not a `ChannelClient` — `take_call_connection`'s
+  detach is wrong for a hub with three `CallConnection` claimants);
+  the reason mapping preserves the spoke's code+message (`timeout` is
+  the one non-1:1 case — it maps to `dial_failed`); the registration
+  seam is two-phase (fork mechanism, §4); the relay map and
+  `channel/close` translation dissolve (implicit mapping + EOF
+  cascade, recorded as the ADR-042 amendment's mechanism supersessions);
+  Pub-typed marked specs are a loud assembly error; establishment
+  bounds compound per hop (noted, no fix).
+- **U-1 shape: combined (b) + (c).** The as-filed option (a) is
+  unsound as stated — the derivation runs consumer-side against a wire
+  JSON payload, so an allowlist "threaded from registration" has no
+  path to `rebuild_spec_for` (both its consumers — `from_call`,
+  `op/register` — are wire-fed). The pinned shape: `spec_to_json_pub`
+  emits an explicit `channel_open_alpn` string alongside the boolean
+  when the op name is not a standard `…/sub`/`…/pub` shape (standard
+  shapes stay byte-identical); `rebuild_spec_for` prefers the explicit
+  string, else generalizes the derivation to strip the LAST segment
+  when the boolean marker is present (the marker is the gate, so any
+  bare-segment flavor works; `op/register` is fixed by the same
+  parser).
+- **U-2 client read path: add the ergonomic accessor now** —
+  `open_channel_with_reply` returning the extra reply fields alongside
+  the streams; `open_channel` unchanged. Keeps alkcall's primary
+  surface intact while giving alktunnels' `TunnelListener::open` a
+  first-class way to read `bound`.
+
+## Unit 1 — U-2: establisher reply projection (ADR-049 amendment 3)
+
+Land first: the relay component (Unit 3a) projects a spoke's extra reply
+fields through `Establishment`, so the projection must exist before the
+e2e can assert `bound` flowing through a relay.
+
+1. `Establishment` gains `reply_fields: Option<Map<String, Value>>` +
+   builder (`Establishment::new(plan).with_reply_field("bound",
+   json!({...}))`; also `with_reply_fields(map)` / `reply_fields()`
+   accessor). `#[non_exhaustive]` holds; additive, no break.
+2. `run_open_wrapper`: on establisher success, merge
+   `reply_fields` into the success output AFTER reserving
+   `channel_id`. An establisher-supplied `channel_id` key is an
+   establisher bug — fail loudly as
+   `EstablishmentError::HandlerError` (reason `handler_error`, message
+   naming the reserved key), tearing the channel down (the wrapper's
+   existing failure path). No silent shadowing.
+3. Client: `ChannelClient::open_channel_with_reply(operation_id, input,
+   alpn) -> Result<(u32, Value, MpscSendStream, MpscRecvStream),
+   ChannelOpenError>` — the full success output (the consumer reads
+   `bound` from it); `open_channel` delegates with the fields
+   discarded. Additive; no signature change.
+4. Doc: ADR-049 amendment 3 (the projection, the `channel_id`
+   reservation, the accessor). The output schema remains the op's own
+   concern (alktunnels' listen-op spec documents `bound` as optional).
+
+Verification gates (from the review, tightened):
+
+- Establisher returning a reply field produces `{ channel_id, bound }`
+  on the wire; one returning none produces `{ channel_id }`
+  (byte-identical to today's — assert exact JSON).
+- Establisher attempting `channel_id` → `channel:open_failed` with
+  reason `handler_error`; channel torn down; ledger decremented.
+- The existing establishment tests (establisher-success pump
+  round-trip, plan-flow, no-establisher compat) pass unchanged.
+- `open_channel_with_reply` returns the extra fields end-to-end over a
+  real channels connection; `open_channel` behavior unchanged.
+
+## Unit 2 — U-1: flavor-form derivation + explicit ALPN field (ADR-047 amendment)
+
+1. `derive_alpn_from_op_name` (`src/client/from_call.rs:305`)
+   generalizes from strip-`/sub`|`/pub` to strip the LAST path segment
+   (`rsplit_once('/')`), which is a strict superset of today's behavior
+   (standard two-suffix shapes derive identically; multi-segment ALPNs
+   survive the same way). The marker boolean remains the gate in
+   `rebuild_spec_for` — the derivation is only consulted for marked
+   ops, so plain ops named `channels/x/y` are unaffected (the
+   `channels/tty/query`-returns-None unit test moves from the function
+   to the marker-gated rebuild level).
+2. `spec_to_json_pub` (`src/registry/discovery.rs:222`): when
+   `channel_open` is set and the op name is NOT a standard
+   `channels/<seg>/(sub|pub)` shape, emit `"channel_open": true` PLUS
+   `"channel_open_alpn": "<alpn>"`. Standard shapes keep the boolean
+   only — byte-stable for every existing consumer. The advertised
+   `operation_spec_schema` (`discovery.rs:159`) gains the optional
+   string property (schema-type widening, additive).
+3. `rebuild_spec_for` (`from_call.rs:209`): prefer the explicit
+   `channel_open_alpn` string; else boolean → generalized derivation.
+   Covers both wire consumers (`from_call`, `op/register`) by
+   construction.
+4. Doc: ADR-047 amendment — the convention sentence mirroring
+   alktunnels ADR-002 Amendment 1 (`channels/<alpn>/<flavor>` is a
+   valid open-op name, `<flavor>` a bare segment; flavors are additive,
+   the `…/sub` op is never reused), the explicit-field wire shape, and
+   the one-way-door note (the field joins the stable
+   `services/schema` payload; the boolean's meaning for standard-shape
+   ops is unchanged). Record the residual ambiguity: an ALPN segment
+   that itself collides with a flavor name (`channels/x/direct` where
+   the ALPN is `alk/x/direct`-shaped) is undecidable from the name
+   alone — the explicit field is the disambiguator.
+
+Verification gates:
+
+- Review gates 1 and 3 as unit/round-trip tests:
+  `rebuild_spec_for("channels/tunnel/direct" summary)` reconstructs
+  WITH `channel_open = alk/tunnel`; `channels/tty/sub` (boolean) and
+  `channels/custom/proto/sub` (multi-segment) round-trip unchanged;
+  flavor-form spec serializes with the explicit string and rebuilds
+  from it; `op/register` announced flavor-form spec round-trips with
+  the marker.
+- Review gate 2 (hub-relay e2e) lands with Unit 3c.
+
+## Unit 3 — the in-tree relay component (ADR-042 amendment, ADR-051) + gate 2 e2e
+
+Adopted 2026-09-17, design pinned in ADR-051 (`docs/architecture/
+decisions/051-channel-relay-and-hub-leg.md`): the relay is the wrapper
+composition (translate hop = the ADR-049 establisher shape; byte-
+forward hop = `pump_bidi` per ADR-050), the ADR-042 relay map
+dissolves (implicit per-channel mapping), `channel/close` needs no
+translation surface (the EOF cascade propagates with correct ledger
+accounting on both legs), and the registration seam is two-phase
+(discover/stash → per-connection fork-register — the ADR-047 §4
+amendment's fork mechanism makes a one-call import impossible without
+adapter changes). The call-half support the hub/spoke family needs is
+the hub-leg install template (Unit 3b) — composition of existing
+pieces, not a new protocol surface. Three sub-units, three sessions'
+scope:
+
+### Unit 3a — `ChannelRelay` (the relay component)
+
+New module `src/channels/relay.rs`:
+
+1. `ChannelRelay::register_relay_openable(consumer_registry, spec,
+   producer_leg)` — for a from_call-imported spec with `channel_open`
+   set, registers on the hub's consumer-leg channel-0 fork registry
+   via `register_openable_with_establisher`, where:
+   - **`producer_leg`** is `Arc<CallConnection>` +
+     producer-leg `ChannelManager` (ADR-051 §2 — not a
+     `ChannelClient`: the hub's `CallConnection` is shared by import,
+     relay establisher, and hub ops, so `take_call_connection`'s
+     detach is wrong; the establisher builds its forwarded payload
+     directly — the hub as caller, the consumer as `forwarded_for`
+     from the per-call identity, ADR-026 §3).
+   - The **establisher** (the translate hop, ADR-042 layer 1): calls
+     the producer leg's open op with the forwarded payload, adopts the
+     returned spoke `channel_id` into the producer-leg manager, and
+     returns `Establishment::new(plan)` whose plan carries the
+     spoke-leg streams. The spoke reply's `channel_id` is stripped;
+     the reply's other fields ride `with_reply_fields` (`bound`
+     flows end-to-end, per-hop truthful). Failure mapping per
+     ADR-051 §3 (the reason table; spoke `CallError` code + message
+     preserved in the mapped variant).
+   - The **OpenHandler** (the byte-forward hop, ADR-042 layer 2):
+     `pump_bidi(consumer_leg_bistream, spoke_recv, spoke_send)` —
+     the relay never parses chunk framing (per-leg mux/demux absorbs
+     the 8-byte header; no ID rewrite exists — ids are
+     per-connection). Awaited inline (R-02); on completion both legs
+     tear down (the wrapper's handler-exit teardown covers the
+     consumer leg; the pump's drops EOF the spoke leg).
+   - The consumer leg keeps the full wrapper machinery: ACL,
+     per-identity cap/ledger, establishment bound (bounds the spoke
+     dial round-trip), teardown-on-failure — no parallel
+     authorization path.
+2. Rejection postures (ADR-051 §6): a `Pub`-typed marked spec is an
+   assembly error at registration (`channel:pub_open_not_implemented`
+   class, C-08 blocker) — never a silent stub; an unmarked spec
+   passed to the relay registration is likewise an error (branch on
+   the marker before calling).
+
+Verification gates:
+
+- The establisher populates `forwarded_for` from the consumer's
+  per-call identity; the spoke reply's `channel_id` is stripped (the
+  consumer reply carries the hub-allocated id).
+- A spoke `channel:open_failed` maps to the consumer-leg
+  `channel:open_failed` with the mapped reason and the spoke's
+  message preserved; consumer leg tears down (ledger decremented);
+  no spoke channel leaks (the adopt-then-fail window is covered).
+- `bound` (Unit 1's projection) survives the relay to the consumer
+  reply.
+- Pub-typed and unmarked specs are rejected at registration.
+
+### Unit 3b — the hub-leg install template (the call-half support)
+
+Landed (2026-09-17): `src/channels/hub_leg.rs` — `HubLegImports`
+(the `Clone` stash split by the marker) and `HubLegTemplate`
+(the §5 composition exported as the `InstallChannelZero` hook;
+`serving identity` via the CF-005 seam). One assembly rule the
+planning sketch missed, surfaced by the template's gate e2e:
+`from_call` discovers the spoke's bootstrap discovery ops like any
+plain op, so the template skips
+`registry::discovery::BOOTSTRAP_DISCOVERY_OPS` when re-registering
+plain bundles — the template's own install (closed over the fork,
+review 004 F-06) supersedes the imported copies. Unit 3c (the
+gate-2 e2e) remains.
+
+The hub-side composition every test hand-rolls
+(`make_install_channel_zero`-shaped), exported in-tree (ADR-051 §5 —
+two-way-door API shape):
+
+1. Fork the hub's base registry (ADR-047 §4 amendment mechanism).
+2. Register the generic channel ops (`ChannelOperations::register_on`)
+   and the bootstrap discovery ops (closed over the fork, so
+   `services/list` sees the fork's ops — review 004 F-06).
+3. Register the stashed plain bundles as-is (the existing forwarding
+   handlers) and the marked specs via Unit 3a's relay registration.
+   The stash is the `Clone`able `Vec<HandlerRegistration>` `from_call`
+   returned (registrations and `HandlerKind` are `Clone`; one
+   discovered set serves any number of consumer legs).
+4. Per-call identity resolution for the serving dispatch
+   (`ServingConfig`-shaped precedence: payload token → explicit
+   override → transport identity), then the single-stream dispatch
+   loop.
+5. Per-consumer op-subset filtering composes here (the fork is per
+   consumer leg — ADR-051 §4's composition note). ACL layering is
+   pinned in ADR-051 §5: the spoke's `AccessControl` sees only the
+   hub identity; the end consumer's identity is `forwarded_for`
+   metadata, never checked by any `AccessControl::check`.
+
+Verification gates:
+
+- The template composes fork + generic ops + bootstrap discovery +
+  plain bundles + relay openables + serving identity and dispatches
+  channel 0; `services/list` on the consumer leg shows the
+  re-exposed ops; a plain imported op round-trips through the hub
+  (the call-half forwarding path exercised for real).
+
+### Unit 3c — gate 2, the review's full e2e harness
+
+The review's verification gate 2, now with the in-tree components:
+
+1. Consumer → hub (Unit 3b's template on the consumer leg;
+   `ChannelsAdapter` both legs) → producer, opening
+   `channels/tunnel/direct` end to end: the open resolves on the
+   consumer with the hub-allocated `channel_id`, the
+   establisher-contributed `bound` field (Unit 1) survives the relay
+   to the consumer reply, data flows both directions on the data
+   channel (the hub never parses it), and hub-side disconnect /
+   spoke-side close tears down both legs' channels.
+2. The mid-establishment disconnect window (ADR-051 §6): consumer
+   leg dies between spoke open and pump spawn — the spoke channel is
+   reclaimed when the pumps run (EOF cascade), both ledgers
+   decremented, no leak.
+3. A companion `channels/tty/sub` relay run pins no regression on
+   standard shapes.
+
+Remaining bookkeeping for the final unit: ADR-042 amendment (landed
+with ADR-051 — the §Scope-note revision and the two mechanism
+supersessions), changelog + minor version bump (new pub API:
+`ChannelRelay`, `register_relay_openable`, the hub-leg template;
+`open_channel_with_reply` and `Establishment::with_reply_field*`
+landed with Units 1–2).
+
+## Sequencing and non-goals
+
+Order: Unit 1 → Unit 2 → Unit 3a → Unit 3b → Unit 3c (Unit 3a is the
+component; 3b the assembly; 3c the e2e gate asserting `bound` through
+the relay — Units 1–2 are prerequisites of 3a; 3b and 3c of each
+other). One release (minor bump), matching the review-007 precedent.
+Not in scope (extends the review's non-asks): the data-plane wire
+format (untouched — the relay rides `MpscSendStream`/`MpscRecvStream`
+and `pump_bidi`; no header rewrite exists — ids are per-connection,
+ADR-051), any `channel/control` translation surface (close propagates
+through the EOF cascade; control is per-leg, OQ-39 — a hub wanting
+cross-leg control translation composes it downstream), the Pub-typed
+open path (rejected loudly; C-08 blocker), and the alktunnels-side
+work (the bind-first establisher, the listen-op spec's `bound`
+documentation, ADR-007/008 implementation) which sequences AFTER these
+land.
+
+Review-008 status updates when units land: mark U-1/U-2 resolved with
+commit refs (the review-007 Status pattern), and correct the U-2 line
+citation (955 → 945) in an errata note rather than silently editing the
+as-filed text.
@@ -0,0 +1,247 @@
+# Review 009 — Post-landing audit of the review-008 remediation (0.7.1 → 0.8.0)
+
+## Status
+
+Resolved — all seven findings landed in alkcall 0.8.0 (2026-09-18,
+same working tree as the audit's inline fixes): C-1 (plain-bundle arm
+pinned + the ADR-051 §5 coverage note), C-2 (`filtered` closure unit +
+the empty-stash e2e gate), C-3 (the batch-form reserved key), C-4
+(the `open_channel_with_reply` failure path), C-5 (both golden pins),
+C-6 (the derivation edge shapes), C-7 (last-win pinned + the doc
+sentence). Three errata on the as-filed text (marked per finding).
+No wire or API changes were needed. Verified at resolution: 680
+tests pass, clippy/fmt clean, wasm check clean.
+
+Open — filed 2026-09-18 from the post-landing audit of the six commits
+`82ddddf..50182d7` (review 008's three units). Scope: correctness
+review of the full diff, test-coverage mapping, and the classic
+implementation-issue sweep. Verified against HEAD at filing (0.8.0 +
+the audit's inline hardening commit): 672 tests pass, clippy/fmt/doc
+clean, wasm check clean.
+
+The audit's code findings were fixed inline at filing time (see the
+CHANGELOG [Unreleased] entry): the adopted-entry leak windows
+(audit F-1/F-2 — `RelayPlan` drop guard), the empty explicit
+`channel_open_alpn` (audit F-3), the `channels//sub` silent-stub
+shape (audit N-4), and the reserved-key message/log-level nits
+(audit N-1/N-2). ADR-051 §6 documents the closed post-adopt window.
+What remains from the audit is the **test-coverage debt** below —
+deliberately deferred to this review so the fix commit stayed small.
+
+Findings continue the review numbering with prefix `C` (coverage).
+
+## Scope
+
+Test-coverage gaps in the 0.8.0 surface: the Unit 3 modules
+(`src/channels/relay.rs`, `src/channels/hub_leg.rs`) and the Unit 1/2
+diff surfaces (`src/channels/operations.rs`, `src/channels/client.rs`,
+`src/client/from_call.rs`, `src/registry/discovery.rs`). No production
+code changes are requested by this review unless a gap's write-up
+says otherwise; each finding names the test(s) to add and what they
+pin. None block a consumer — the e2e gates the review-008 plan pinned
+are all landed and passing; these gaps are the paths the gates never
+walk.
+
+## C-1: `HubLegTemplate::install_hook` failure arms are loud-only-in-code
+
+**Errata (2026-09-18, at resolution).** The as-filed route (a) —
+"a duplicate name between a plain bundle and the generic channel ops"
+— does not fail `OperationRegistry::register` (same-name registration
+overwrites; the map is an insert). The honest failure mechanism used
+is the registry's other fail-closed rule: an un-compilable
+`input_schema` (`{"type": "object", "required": "not-an-array"}`,
+the CF-003 shape). Resolved with route (c)'s documentation half for
+the generic-ops/bootstrap-discovery arms: ADR-051 §5 now carries the
+loud-install coverage note (two arms pinned, two arms
+best-effort-loud — the crate-internal specs compile by construction,
+so an injectable seam would test the seam, not the arm).
+
+**Finding.** `src/channels/hub_leg.rs:232-275` — four install arms end
+the leg with only a `tracing::warn!`: generic channel ops registration
+failure, plain-bundle registration failure, relay-openable
+registration failure, bootstrap-discovery install failure. ADR-051 §6
+pins the posture as "loud, never a silent stub" and only the
+relay-openable arm is test-pinned
+(`hub_leg_tests.rs` `template_pub_typed_marked_spec_is_loud_at_install`).
+The other three are near-unreachable (generic ops and bootstrap
+discovery cannot realistically fail; plain bundles were already
+registered on the producing side) — but the ADR's posture claim rests
+on code that no test walks.
+
+**Requested change.** Unit-test the three unpinned arms. The plain
+routes: (a) a plain bundle that fails registration — e.g. a duplicate
+name between a plain bundle and the generic channel ops — asserts the
+install task ends before `run_loop_single_stream`; (b) the same shape
+for a relay-openable failure is already pinned; (c) the
+generic-ops/bootstrap-discovery arms need an injectable failure seam
+if they are to be tested honestly — if that is disproportionate,
+instead demote the claim: document in ADR-051 §5 that only the
+relay-openable arm is test-pinned and the others are
+best-effort-loud, so the ADR and the code say the same thing.
+
+**Verification gates:**
+
+1. The template's install task provably ends (channel 0 never
+   dispatches) on each exercised failure arm.
+2. The ADR-051 §5/§6 text matches what is actually pinned.
+
+## C-2: `HubLegImports::filtered` / `only` have no test
+
+**Errata (2026-09-18, at resolution).** The as-filed "no unit test"
+overstated: `stash_filter_keeps_named_ops_only` (landed with Unit 3b)
+already exercised `only` at filing time. The real gaps — the
+`filtered` closure path and the empty-filter e2e shape — are what
+landed (`stash_only_keeps_the_marked_direct_spec_and_drops_the_rest`,
+`stash_filtered_closure_partitions_both_halves`,
+`template_empty_only_stash_installs_generic_ops_and_discovery_only`).
+
+**Finding.** `src/channels/hub_leg.rs:91-111` — the per-consumer
+op-subset filter, the mechanism behind ADR-051 §4's "per-consumer ACL
+differentiation is a composition consequence" note, has no unit test.
+Trivial code, but it is exported pub API (`HubLegImports` is a crate
+export) and the filter story is load-bearing for the hub/spoke family.
+
+**Requested change.** Unit tests: `from_bundles` splits by marker;
+`filtered`/`only` partition both halves; a `#[must_use]` misuse
+compiles with a warning (already enforced by the attribute — just
+exercise the two builders).
+
+**Verification gates:**
+
+1. `only(&["channels/tunnel/direct"])` keeps the marked direct spec,
+   drops everything else, plain bundle untouched by the marked list.
+2. An empty `only` stash installs a leg that serves only the generic
+   ops + discovery (no re-exposed ops in `services/list`).
+
+## C-3: Batch-form reserved reply key
+
+**Finding.** `src/channels/operations.rs` — the reserved-key teardown
+test (`with_reply_field("channel_id", …)`, `operations.rs:~2606`)
+covers only the builder form. The wrapper's check inspects the merged
+map, so `with_reply_fields(map)` smuggling `channel_id` is covered by
+construction — but the batch path is the shape a hub's
+`Establishment::with_reply_fields(relay_map)` will actually use, and
+it is unasserted.
+
+**Requested change.** One-line extension of the existing test (or a
+sibling): the batch form fails with reason `handler_error`, channel
+torn down, ledger decremented.
+
+**Verification gates:**
+
+1. `Establishment::default().with_reply_fields(json_map_containing_channel_id)`
+   → `channel:open_failed` / `handler_error`; `count_for == 0` after.
+
+## C-4: `open_channel_with_reply` wire failure path
+
+**Finding.** `src/channels/client.rs:1654` — the new client API's e2e
+test covers the success path only. The failure path (a
+`channel:open_failed` resolving through `open_channel_with_reply`) is
+covered only indirectly (wrapper-level test + the generic
+`establisher_failure_resolves_typed_open_failed_on_the_client`).
+Low risk — the parse path is shared with `open_channel` — but the new
+pub API's error path has no direct pin.
+
+**Requested change.** One e2e test against the existing
+establisher-always-fails harness: `open_channel_with_reply` resolves
+`Err(ChannelOpenError::CallFailed)` with the `channel:open_failed`
+code and details intact.
+
+**Verification gates:**
+
+1. The full reply shape (`reason`, `message` in `details`) is
+   assertable by the caller through the new API.
+
+## C-5: Byte-identical claims are shape-pinned, not golden-pinned
+
+**Finding.** Two "byte-identical" claims are pinned structurally
+(key-set equality), not by literal:
+
+- `run_open_wrapper_without_reply_fields_is_byte_identical_to_pre_amendment`
+  (`operations.rs:2553`) asserts `v == json!({"channel_id":
+  v["channel_id"]})` — pins the exact key set but builds the expected
+  from the actual (a wrong-typed `channel_id` value would pass).
+- The Unit-2 standard-shape wire payload
+  (`spec_standard_shape_channel_open_stays_boolean_only`) pins the
+  key *absence* of `channel_open_alpn` (the real pin, solid) but not
+  the payload's full key set.
+
+**Requested change.** Golden-pin both: assert serialized bytes or a
+literal `json!` against the actual for the no-fields reply, and a
+full-object comparison for the standard-shape payload. Cheap, and it
+converts "structurally equal" into "these exact bytes" for the two
+claims the ADRs advertise as wire-stable.
+
+**Verification gates:**
+
+1. The no-fields open reply equals `json!({"channel_id": <exact
+   literal>})` — not a self-referential compare.
+2. The standard-shape `services/schema` payload compares equal to a
+   literal object including key order (serde_json default map).
+
+## C-6: `derive_alpn_from_op_name` edge shapes unpinned
+
+**Errata (2026-09-18, at resolution).** The as-filed expectation
+`"channels/x/sub/extra"` → `Some("alk/x/sub")` mis-stated the actual
+behavior: the last-segment strip yields `rest = "x/sub/extra"`, and
+`x/sub` (multi-segment, non-`alk/*`) rides as a full ALPN per the
+ALPNs-without-the-prefix rule — `Some("x/sub")`, the same rule the
+existing 5-segment test (`vendor/service/run`) pins. The landed test
+asserts the actual behavior with the behavior-change-vs-pre-amendment
+annotation.
+
+**Finding.** `src/client/from_call.rs:326-337` — the empty-segment
+guard (`segment.is_empty()`) and the bare-no-slash name have no unit
+test, and the 4-segment name behavior *changed* (pre-amendment:
+`None`; now: `Some("x/sub")`) without any test noticing. The audit
+closed the `channels//sub` serialization half (N-4); the derivation
+function's own edge-shape unit tests remain unlanded.
+
+**Requested change.** Unit tests over the derivation directly:
+`"channels//sub"` → `None`; `"channels//direct"` → `None`;
+`"channels"` → `None`; `"channels/x/sub/extra"` → `Some("alk/x/sub")`
+(the deliberate strict-superset behavior, worth pinning as intended);
+`"channels/alk/tty/sub"` → `Some("alk/tty")` (the verbatim case).
+
+**Verification gates:**
+
+1. All five shapes assert as above; the 4-segment case is annotated
+   as a behavior change vs the pre-amendment derivation.
+
+## C-7: Builder overwrite semantics unpinned
+
+**Finding.** `src/channels/operations.rs:420-434` — two
+`with_reply_field("same-key", …)` calls silently last-win; the batch
+form extends (also last-win). Establisher-own concern, nit-level, but
+it is pub-API behavior a consumer will rely on or be confused by.
+
+**Requested change.** Either pin last-win with a test (and one doc
+sentence on `with_reply_field`), or reject duplicates loudly at
+build time. Prefer pinning: rejection adds a failure mode with no
+consumer ask behind it.
+
+**Verification gates:**
+
+1. `.with_reply_field("k", v1).with_reply_field("k", v2)` →
+   `reply_fields()["k"] == v2`.
+
+## Non-goals (recorded to bound the review)
+
+- **No wire-format or API changes** — everything above is tests plus
+  at most doc text. The audit's code findings are already landed;
+  they are not re-opened here.
+- **No new ADRs** — C-1's documentation route (if chosen) edits
+  ADR-051 §5/§6 text only.
+- **alktunnels-side work** (the bind-first establisher, the listen-op
+  spec) sequences after this review as planned; nothing here blocks
+  it.
+
+## References
+
+- ADR-051 §6 (the post-adopt teardown bullet the drop guard landed;
+  C-1 pins its assembly-arm siblings)
+- ADR-047 amendment 3 (C-6's derivation shapes), ADR-049 amendment 3
+  (C-3/C-7's reply projection), ADR-047 (C-5's wire-stability claims)
+- CHANGELOG [Unreleased] — the audit's inline fixes this review
+  complements
+- Review 008 — the remediation whose surface this review audits
@@ -17,6 +17,135 @@ Format: date | found-in (alkhttp context) | severity | status.

 ## Resolved

+### CF-005 — connect-side serving path (`from_connection_with_serving`) has no caller-identity capture; scope-gated ops are satisfiable only via payload `auth_token` (2026-09-07) — RESOLVED 2026-09-07
+
+- **Found in:** alktunnels reverse-flow POC
+  (`alktunnels-reverse-poc`, summary at
+  `/workspace/@alkdev/alktunnels/docs/research/reverse-poc-summary.md`
+  §W1; verified against alkcall 0.6.0). The worker is the connect side
+  AND the serving side (ADR-022 §2 both-sides): it serves its tunnel
+  open op to the hub over the connection it dialed. The open op is
+  scope-gated (`AccessControl.required_scopes`), but the identity the
+  ACL sees comes from `Dispatcher::dispatch_start` →
+  `resolve_identity(connection_identity, payload)`, and:
+  - `connection.identity()` is `None` — `from_connection_with_serving`
+    builds channel 0 internally via `Connection::from_source`
+    (`client.rs` channel-0 block) and never sets an identity; there is
+    no capture point for the transport-authenticated peer
+    (mTLS/QUIC identity) on this path.
+  - The only caller-identity path is the payload `auth_token` →
+    `ServingConfig.identity_provider` (`resolve_from_token`).
+  - Corollary: the `AuthContext` closed over by
+    `register_openable*`'s wrapper (what the establisher and pump
+    handler receive) is the connection-establishment-time context, not
+    the per-call opener's identity — on the accept side the install
+    hook receives the transport `AuthContext` and can
+    `channel0_conn.set_identity`, but `from_connection_with_serving`
+    has no equivalent seam.
+- **Impact:** a connect-side serving op with a scope gate cannot
+  authenticate the legitimate peer by transport identity — the POC
+  had to attach `auth_token` payloads from the hub side
+  (`CallConnection::call_with_payload`). Acceptable for hub-forwarding
+  topologies (from_call's ADR-017 §7 token path), but a gap for
+  direct connect-side serving where the transport already
+  authenticated the peer.
+- **Verification:** confirmed statically (the chain
+  `Connection::from_source` → empty `OnceLock` identity →
+  `dispatch_start` → `resolve_identity(None, payload)` →
+  `AccessControl::check(None)` fails closed) and empirically (e2e
+  duplex tests reproducing the POC shape; the tokenless scope-gated
+  call was denied `FORBIDDEN: authentication required` while the
+  token path succeeded).
+- **Fix (both remediations (a) + (b), 2026-09-07):** the caller
+  identity for the connect-side serving dispatch resolves in
+  precedence order — (1) payload `auth_token` →
+  `ServingConfig.identity_provider` (unchanged; the hub-forwarding /
+  browser-token fallback, ADR-017 §7); (2) new
+  `ServingConfig.identity: Option<Identity>` — the explicit override
+  (remediation (a)); (3) the transport connection's identity,
+  propagated automatically: `from_connection_with_serving` copies
+  `connection.identity()` to the channel-0 connection via
+  `set_identity` before the serving loop starts (remediation (b) —
+  the native-client mTLS/QUIC key-based path; mirrors the accept
+  side's install-hook `set_identity`). Also added the public
+  `core::auth::NoopIdentityProvider` (resolves nothing) — the
+  identity-less posture and the `ServingConfig::default()`
+  identity provider; three private test copies of it existed.
+  - **Behavior change (semver-relevant):** `ServingConfig` gained an
+    `identity` field — struct literals must add `identity: None`
+    (0.x; changelog note). The call half is unaffected
+    (`spawn_dispatch` takes the consumer-owned `Connection`, so the
+    consumer can `set_identity` before wrapping).
+  - The corollary (`register_openable`'s closed-over
+    establishment-time `AuthContext` vs the per-call opener identity)
+    was resolved in the same batch (2026-09-07, CF-006 below).
+- **Status:** resolved — 2026-09-07 (regression gates: `cf005_*`
+  tests in `src/channels/client.rs`).
+
+### CF-006 — open-op establisher/pump handler receive the install-time `AuthContext`, never the per-call opener's identity (CF-005 corollary) (2026-09-07) — RESOLVED 2026-09-07
+
+- **Found in:** the CF-005 verification pass (same alktunnels
+  reverse-flow POC W1 material; the ledger's CF-005 entry named it as
+  a "design follow-up, tracked separately"). `run_open_wrapper`
+  (`src/channels/operations.rs`) closed over the
+  `install_channel_zero`-time `AuthContext` and passed `auth.clone()`
+  verbatim to both the establisher (ADR-049 §1) and the pump handler
+  (`OpenHandler`'s 4th parameter). The per-call opener's identity —
+  the same identity the ACL gate and the per-identity cap check saw —
+  reached neither hook. On a per-connection registry (ADR-047 §4)
+  install-time identity IS the caller's, so the gap was invisible
+  there; it shows on hub-forwarded opens (the establisher saw the
+  hub, not the end client) and on the connect-side serving path
+  (token- or `ServingConfig.identity`-resolved callers). alktty
+  review 002 R3 independently recorded the same seam (closed
+  per-connection by design, with the "registry must stay
+  per-connection" constraint).
+- **Impact:** an establisher doing per-principal authorization or
+  ownership checks on the backend could not see the actual opener;
+  the pump handler tagging sessions by principal saw the hub.
+- **Fix (2026-09-07):** `run_open_wrapper` derives a **per-call
+  `AuthContext`** — the opener's dispatch-resolved identity overlaid
+  onto the install-time context — and passes it to both the
+  establisher and the pump handler. When the call has no resolved
+  identity, the install-time identity is kept (anonymous-keep; no
+  synthetic-`anonymous` rewrite of a real install-time identity).
+  Transport-truthful fields (`alpn`, `remote_addr`,
+  `tls_client_fingerprint`) are never rewritten. Signatures are
+  unchanged (`OpenEstablisher`, `OpenHandler` still take
+  `AuthContext`) — behavior-only, additive; downstream code compiles
+  unchanged. Regression gates:
+  `open_wrapper_overlays_per_call_identity_on_install_time_auth` +
+  `open_wrapper_keeps_install_time_identity_when_call_identityless`
+  in `src/channels/operations.rs`.
+- **Also in this batch:** `ChannelPlan`'s type doc now spells out the
+  `Send + Sync` payload constraint (alktunnels POC F-1 re-derived it
+  by compiler error — a doc line prevents the next consumer repeating
+  that).
+- **Status:** resolved — 2026-09-07.
+
+### CF-007 — ADR-016's protocol-code list is stale: omits `ALREADY_EXISTS` and `CONNECTION_CLOSED` (2026-09-07) — RESOLVED 2026-09-07
+
+- **Found in:** alkhttp review 006, Part C
+  (`alkhttp/docs/reviews/006-alkcall-0.3.0-consequence-review.md`
+  L207–233, L319–324 — "upstream doc drift … flagged for the next
+  alkcall doc pass"). ADR-016 said "six codes" and its table listed
+  only the original six, while the wire vocabulary had grown:
+  `ALREADY_EXISTS` (ADR-022 collision sub-amendment, 0.3.0) and
+  `CONNECTION_CLOSED` (CF-001, 0.4.x, the retryable
+  provably-undelivered-call code). Downstream consumers already
+  handle both; the authoritative ADR was the thing that was wrong.
+- **Fix (2026-09-07):** ADR-016 amended — Status notes the 2026-09-07
+  extension to eight; the Context paragraph and the §3 table carry
+  both codes with their semantics (`ALREADY_EXISTS` non-retryable,
+  registration state; `CONNECTION_CLOSED` retryable — the only
+  protocol code a caller may auto-retry), a §2a subsection documents
+  the undelivered-vs-ambiguous write-failure distinction, the
+  `from_openapi` collision rule lists all eight, and the
+  cross-references cite the two amendments. Doc-only; the wire
+  surface is unchanged.
+- **Status:** resolved — 2026-09-07.
+
+---
 ### CF-004 — `services_schema_handler` discloses Internal/ACL-restricted op specs — no visibility or AccessControl check (2026-08-30) — RESOLVED 2026-08-31

 - **Found in:** alkhttp Review 002, finding PRJ-16
@@ -0,0 +1,6 @@
+target
+corpus/*
+!corpus/chunk_header
+!corpus/envelope_frame
+artifacts
+coverage
@@ -0,0 +1,52 @@
+[package]
+name = "alkcall-fuzz"
+version = "0.0.0"
+publish = false
+edition = "2021"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+alkcall-fuzz-shared = { path = "shared" }
+
+[dependencies.alkcall]
+path = ".."
+
+[[bin]]
+name = "chunk_header"
+path = "fuzz_targets/chunk_header.rs"
+test = false
+doc = false
+bench = false
+
+[[bin]]
+name = "envelope_frame"
+path = "fuzz_targets/envelope_frame.rs"
+test = false
+doc = false
+bench = false
+
+[[bin]]
+name = "manager_routing"
+path = "fuzz_targets/manager_routing.rs"
+test = false
+doc = false
+bench = false
+
+[[bin]]
+name = "envelope_semantic"
+path = "fuzz_targets/envelope_semantic.rs"
+test = false
+doc = false
+bench = false
+
+[[bin]]
+name = "spec_parse"
+path = "fuzz_targets/spec_parse.rs"
+test = false
+doc = false
+bench = false
+
+[workspace]
@@ -0,0 +1,53 @@
+# alkcall fuzzing
+
+libFuzzer targets for alkcall's wire formats (see
+`docs/research/fuzzing.md` for the full rationale and campaign plan).
+
+## Layout
+
+- `fuzz_targets/` — one binary per target; thin `fuzz_target!` wrappers.
+- `shared/` — the invariant logic, as a plain library so normal
+  `cargo test` (stable toolchain) can replay the committed corpora
+  through the same invariants (`fuzz/shared/src/*.rs` `#[cfg(test)]`
+  modules; quinn's CI pattern). The fuzz binaries are nightly-only;
+  the shared crate is stable-clean.
+- `corpus/<target>/` — committed hand-made seeds (regenerate with
+  `python3 fuzz/gen_fuzz_seeds.py` from the repo root). Grown corpora
+  and artifacts are gitignored.
+- `run-detached.sh` — mandatory runner for agent sessions: wraps
+  `cargo fuzz run` in `setsid` + `nohup` + log redirection so an OOM
+  in a target can never take down the agent host (research doc §7.6).
+- `json.dict` — JSON token dictionary for the envelope targets.
+
+## Targets
+
+| Target | Drives | Invariants |
+|---|---|---|
+| `chunk_header` | `parse_header` / `write_header` (`channels/wire.rs`) | no-panic; round-trip identity; `TooLarge` iff `length > MAX_CHUNK_LEN`; consumption accounting (8 bytes); input never mutated |
+| `envelope_frame` | `FrameFramedReader::new(Cursor).read_frame()` on a current-thread runtime | no-panic; never allocates > `MAX_FRAME_SIZE`; clean `FrameError` on truncation/oversize/zero-length; exact consumption; structural `write_frame` round-trip |
+
+## Commands
+
+`cargo fuzz build` and `cargo fuzz run` must be executed with `fuzz/`
+(or deeper) as the working directory so rustup selects the pinned
+nightly toolchain — the detached runner handles that itself.
+
+```sh
+# build (nightly, pinned by rust-toolchain.toml inside fuzz/; run from fuzz/)
+cargo fuzz build
+
+# agent sessions: detached campaign (never foreground; CWD-independent)
+FUZZ_RUNTIME_SECS=600 fuzz/run-detached.sh chunk_header
+FUZZ_RUNTIME_SECS=600 fuzz/run-detached.sh envelope_frame -max_len=65536 -dict=json.dict
+
+# corpus replay through the invariants (stable toolchain, no nightly)
+cargo test --manifest-path fuzz/shared/Cargo.toml
+
+# coverage
+cargo fuzz coverage <target>
+```
+
+The fuzz workspace is excluded from the main workspace and from the
+published package (`exclude` in the root `Cargo.toml`); it pins its own
+nightly toolchain via `rust-toolchain.toml` and does not affect the
+crate's stable MSRV.
@@ -0,0 +1 @@
+��������
@@ -0,0 +1 @@
+
@@ -0,0 +1 @@
+
@@ -0,0 +1 @@
+
@@ -0,0 +1 @@
+
@@ -0,0 +1 @@
+
@@ -0,0 +1 @@
+
@@ -0,0 +1 @@
+