feat(review 006 Unit 3): teardown-race log, early-arrival bound docs, count accessor (E-03, E-04, N-2)

- E-03: the open wrapper's handler-exit teardown no longer discards UnknownChannel silently — debug log + benign-race pinning comment (ledger take is the atomic gate; no double-decrement) - E-04: consumer-facing doc note on the 64-parked-chunks observable bound (channel-client.md + EARLY_ARRIVAL_CAP const doc) for tunnel-style push-first producers - N-2: ChannelManager::early_arrival_count() accessor (the observability choice over removing the write-only counter), documented monotonic, with a park/adopt-drain monotonicity test - review 006: Unit 3 marked implemented in Status and remediation plan Verification: 617 tests pass; clippy -D warnings clean (host + wasm32 check); fmt clean; doc clean
feat(review 006 Unit 2): additive OperationSpec.description disclosed via discovery (E-02)
2026-09-06 19:35:18 +00:00 · 2026-09-06 19:26:51 +00:00 · 2026-09-06 19:00:04 +00:00 · 2026-09-06 10:57:20 +00:00 · 2026-09-06 09:54:13 +00:00
16 changed files with 2348 additions and 32 deletions
@@ -4,6 +4,55 @@ 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/).

+## [0.5.0] - 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
@@ -27,7 +27,7 @@ dependencies = [

 [[package]]
 name = "alkcall"
-version = "0.4.1"
+version = "0.5.0"
 dependencies = [
 "async-trait",
 "bytes",
@@ -1,6 +1,6 @@
 [package]
 name = "alkcall"
-version = "0.4.1"
+version = "0.5.0"
 edition = "2021"
 rust-version = "1.85"
 license = "MIT OR Apache-2.0"
@@ -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
@@ -8,7 +8,40 @@ 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 (§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 +1,356 @@
+# 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
+
+## 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).
+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).
@@ -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 +1,561 @@
+# 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).
@@ -25,13 +25,69 @@ use tokio::sync::Mutex;

 use crate::core::types::{Connection, StreamError};
 use crate::protocol::connection::CallConnection;
-use crate::protocol::wire::ResponseEnvelope;
+use crate::protocol::wire::{CallError, ResponseEnvelope};
 use crate::registry::registration::OperationRegistry;

 use super::manager::{ChannelManager, ChannelSide};
 use super::mux::MuxRunner;
 use super::reassembly::{MpscRecvStream, MpscSendStream};

+/// The typed error from [`ChannelClient::open_channel`] (ADR-049 §4 —
+/// review 006 N-1). The open op's `CallError` — including the
+/// `channel:open_failed` code with `details: { reason, message }`
+/// (ADR-049 §3) — is carried verbatim instead of flattened into a
+/// string, so the consumer can branch on the establishment-failure
+/// reason (`dial_failed`, `unknown_resource`, `resource_shortage`,
+/// `handler_error`, `timeout`).
+#[derive(Debug, Clone, PartialEq, thiserror::Error)]
+pub enum ChannelOpenError {
+    /// The open op failed — the `CallError` carries the wire code and
+    /// typed `details` (`channel:open_failed` + `details.reason` per
+    /// ADR-049 §3, `channel:too_many_channels`, `FORBIDDEN`, …).
+    #[error("open op failed: {error:?}")]
+    CallFailed { error: CallError },
+    /// The open op succeeded but the response carried no `channel_id`
+    /// (malformed responder).
+    #[error("open op response missing channel_id")]
+    MissingChannelId,
+    /// The open op succeeded but local channel adoption failed (the
+    /// per-connection cap, or an ID collision).
+    #[error("adopt_channel failed: {0}")]
+    AdoptFailed(#[from] super::manager::ManagerError),
+}
+
+impl ChannelOpenError {
+    /// The wire `CallError` behind this failure, when the open op
+    /// itself failed. `None` for the local-only variants
+    /// (`MissingChannelId` comes from a success envelope;
+    /// `AdoptFailed` is post-reply).
+    pub fn call_error(&self) -> Option<&CallError> {
+        match self {
+            ChannelOpenError::CallFailed { error } => Some(error),
+            ChannelOpenError::MissingChannelId | ChannelOpenError::AdoptFailed(_) => None,
+        }
+    }
+
+    /// The establishment-failure reason code — `details.reason` of a
+    /// `channel:open_failed` error (`dial_failed`, `unknown_resource`,
+    /// `resource_shortage`, `handler_error`, `timeout`). `None` for
+    /// any other failure shape.
+    pub fn establishment_reason(&self) -> Option<&str> {
+        match self {
+            ChannelOpenError::CallFailed { error }
+                if error.code == super::operations::CHANNEL_OPEN_FAILED =>
+            {
+                error
+                    .details
+                    .as_ref()
+                    .and_then(|d| d.get("reason"))
+                    .and_then(|r| r.as_str())
+            }
+            _ => None,
+        }
+    }
+}
+
 /// The client-side handle for a channels connection. Constructed via
 /// [`ChannelClient::from_connection`] from an established
 /// `Connection`. Holds the `ChannelManager` (for the demux/mux state)
@@ -224,26 +280,33 @@ impl ChannelClient {
    ///
    /// `alpn` is the data-plane ALPN (e.g. `alk/tty`), used for
    /// observability in the local manager.
+    ///
+    /// The error is typed (ADR-049 §4 — review 006 N-1): a failed open
+    /// resolves [`ChannelOpenError::CallFailed`] carrying the
+    /// wire `CallError` verbatim — branch on
+    /// [`ChannelOpenError::establishment_reason`] for
+    /// `channel:open_failed`'s reason code (`dial_failed`,
+    /// `unknown_resource`, `resource_shortage`, `handler_error`,
+    /// `timeout`).
    pub async fn open_channel(
        &self,
        operation_id: &str,
        input: Value,
        alpn: &str,
-    ) -> Result<(u32, MpscSendStream, MpscRecvStream), String> {
+    ) -> Result<(u32, MpscSendStream, MpscRecvStream), ChannelOpenError> {
        let response = self.call_open_op(operation_id, input).await;
        let out = response
            .result
-            .map_err(|e| format!("open op failed: {e:?}"))?;
+            .map_err(|error| ChannelOpenError::CallFailed { error })?;
        let channel_id = out
            .get("channel_id")
            .and_then(|v| v.as_u64())
-            .ok_or_else(|| "open op response missing channel_id".to_string())?
-            as u32;
+            .ok_or(ChannelOpenError::MissingChannelId)? as u32;

        self.manager
            .adopt_channel(channel_id, alpn, None)
            .await
-            .map_err(|e| format!("adopt_channel failed: {e}"))
+            .map_err(ChannelOpenError::AdoptFailed)
            .map(|(send, recv)| (channel_id, send, recv))
    }

@@ -1256,6 +1319,260 @@ mod tests {
        );
    }

+    /// ADR-049 Unit 1 acceptance gate (review 006 E-01/N-1) — the
+    /// establisher fails after channel allocation: the consumer's
+    /// `open_channel` resolves `Err` carrying the wire `CallError`
+    /// (`channel:open_failed` + `details.reason`), no `channel_id` was
+    /// ever returned (the SSH "channel never exists opener-side"
+    /// property, consumer-visible), and the accept side's manager has
+    /// no channel afterward (teardown + ledger un-increment).
+    #[tokio::test]
+    async fn establisher_failure_resolves_typed_open_failed_on_the_client() {
+        use crate::channels::operations::{
+            ChannelCore, EstablishmentError, OpenEstablisher, OpenHandler,
+        };
+        use crate::channels::policy::PerIdentityChannelPolicy;
+        use crate::registry::spec::ChannelOpenSpec;
+
+        let policy: Arc<PerIdentityChannelPolicy> = Arc::new(PerIdentityChannelPolicy::new(256));
+        let policy_for_hook: Arc<dyn ChannelLifecyclePolicy> =
+            Arc::clone(&policy) as Arc<dyn ChannelLifecyclePolicy>;
+        let policy_for_assert = Arc::clone(&policy);
+
+        let open_handler: OpenHandler =
+            Arc::new(|_input, _channel_conn, _auth| tokio::spawn(async {}));
+        let establisher: OpenEstablisher = Arc::new(|_input, _auth| {
+            Box::pin(async {
+                Err(EstablishmentError::DialFailed {
+                    message: "target refused the connection".to_string(),
+                })
+            })
+        });
+
+        let install_hook: crate::channels::adapter::InstallChannelZero =
+            Arc::new(move |manager, channel0_conn, auth| {
+                let open_handler = Arc::clone(&open_handler);
+                let establisher = Arc::clone(&establisher);
+                let policy = Arc::clone(&policy_for_hook);
+                tokio::spawn(async move {
+                    let channel0_bidi = match channel0_conn.accept_bi().await {
+                        Ok(s) => s,
+                        Err(_) => return,
+                    };
+                    let (writer, reader) = split_single_stream(channel0_bidi);
+                    let core = ChannelCore::new(manager, policy);
+                    let registry = crate::registry::registration::OperationRegistry::new();
+                    let spec = OperationSpec::new(
+                        "channels/tty/sub",
+                        OperationType::Sub,
+                        Visibility::External,
+                        serde_json::json!({}),
+                        serde_json::json!({
+                            "type": "object",
+                            "properties": { "channel_id": { "type": "integer" } }
+                        }),
+                        vec![],
+                        AccessControl::default(),
+                        None,
+                    )
+                    .with_channel_open(ChannelOpenSpec::new("alk/tty"));
+                    core.register_openable_with_establisher(
+                        spec,
+                        Some(establisher),
+                        open_handler,
+                        &registry,
+                        auth.clone(),
+                        None,
+                    )
+                    .expect("register_openable_with_establisher");
+                    let registry = Arc::new(registry);
+                    let provider: Arc<dyn IdentityProvider> = Arc::new(NoopIdProvider);
+                    let call_connection = Arc::new(CallConnection::new_single_stream(
+                        channel0_conn,
+                        Arc::clone(&writer),
+                    ));
+                    let dp = Dispatcher::new(registry, provider);
+                    dp.run_loop_single_stream(call_connection, reader, writer)
+                        .await;
+                })
+            });
+
+        let (client_end, server_end) = tokio::io::duplex(64 * 1024);
+        let client_conn =
+            Connection::from_bidi(client_end, b"alk/channels".to_vec(), Some(TEST_ADDR));
+        let server_conn =
+            Connection::from_bidi(server_end, b"alk/channels".to_vec(), Some(TEST_ADDR));
+
+        let adapter = ChannelsAdapter::new(install_hook, Arc::new(NoCap));
+        let auth = AuthContext::anonymous(b"alk/channels");
+        let _server_handle = tokio::spawn(async move {
+            let _ = crate::core::types::ProtocolHandler::handle(&adapter, server_conn, &auth).await;
+        });
+
+        let client = ChannelClient::from_connection(client_conn)
+            .await
+            .expect("channel client init");
+
+        let err = tokio::time::timeout(
+            std::time::Duration::from_secs(10),
+            client.open_channel(
+                "channels/tty/sub",
+                serde_json::json!({ "container": "abc" }),
+                "alk/tty",
+            ),
+        )
+        .await
+        .expect("open_channel timed out");
+        let err = match err {
+            Err(e) => e,
+            Ok(_) => panic!("establisher failure must resolve Err through the client"),
+        };
+
+        // N-1 gate: the typed error carries the wire CallError verbatim.
+        let call_error = err.call_error().expect("CallFailed carries the CallError");
+        assert_eq!(call_error.code, "channel:open_failed");
+        assert_eq!(
+            err.establishment_reason(),
+            Some("dial_failed"),
+            "consumer branches on the typed reason code"
+        );
+
+        // The SSH property, consumer-visible: no channel_id was ever
+        // returned, and the accept side holds no channel for the failed
+        // open (channel 0 is the pre-negotiated call channel — always
+        // present, never the failed open's).
+        assert!(
+            client.manager().channel_ids().into_iter().all(|id| id == 0),
+            "no data channel exists for the failed open"
+        );
+        let anonymous = crate::core::auth::Identity {
+            id: "anonymous".to_string(),
+            scopes: vec![],
+            resources: Default::default(),
+        };
+        assert_eq!(
+            policy_for_assert.count_for(&anonymous),
+            0,
+            "ledger un-incremented on the accept side after establishment failure"
+        );
+    }
+
+    /// ADR-049 Unit 1 acceptance gate (companion to the E-01 gate) —
+    /// establisher success through a real channels connection: the
+    /// client's `open_channel` adopts and the pumps flow (the happy
+    /// path is unchanged by the establishment phase).
+    #[tokio::test]
+    async fn establisher_success_opens_and_pumps_data_end_to_end() {
+        use crate::channels::operations::{
+            ChannelCore, Establishment, OpenEstablisher, OpenHandler,
+        };
+        use crate::channels::policy::NoCap;
+        use crate::registry::spec::ChannelOpenSpec;
+        use tokio::io::AsyncReadExt;
+
+        let (data_tx, mut data_rx) = tokio::sync::mpsc::channel::<Vec<u8>>(1);
+
+        let open_handler: OpenHandler = Arc::new(move |_input, channel_conn, _auth| {
+            let data_tx = data_tx.clone();
+            tokio::spawn(async move {
+                let mut bidi = channel_conn.accept_bi().await.expect("accept_bi");
+                let mut buf = [0u8; 4];
+                bidi.read_exact(&mut buf).await.expect("read");
+                data_tx.send(buf.to_vec()).await.expect("send to channel");
+            })
+        });
+        let establisher: OpenEstablisher =
+            Arc::new(|_input, _auth| Box::pin(async { Ok(Establishment::default()) }));
+
+        let establisher_for_hook = Arc::clone(&establisher);
+        let open_handler_for_hook = Arc::clone(&open_handler);
+        let install_hook: crate::channels::adapter::InstallChannelZero =
+            Arc::new(move |manager, channel0_conn, auth| {
+                let establisher = Arc::clone(&establisher_for_hook);
+                let open_handler = Arc::clone(&open_handler_for_hook);
+                tokio::spawn(async move {
+                    let channel0_bidi = match channel0_conn.accept_bi().await {
+                        Ok(s) => s,
+                        Err(_) => return,
+                    };
+                    let (writer, reader) = split_single_stream(channel0_bidi);
+                    let core = ChannelCore::new(manager, Arc::new(NoCap));
+                    let registry = crate::registry::registration::OperationRegistry::new();
+                    let spec = OperationSpec::new(
+                        "channels/tty/sub",
+                        OperationType::Sub,
+                        Visibility::External,
+                        serde_json::json!({
+                            "type": "object",
+                            "properties": { "container": { "type": "string" } },
+                            "required": ["container"]
+                        }),
+                        serde_json::json!({
+                            "type": "object",
+                            "properties": { "channel_id": { "type": "integer" } }
+                        }),
+                        vec![],
+                        AccessControl::default(),
+                        None,
+                    )
+                    .with_channel_open(ChannelOpenSpec::new("alk/tty"));
+                    core.register_openable_with_establisher(
+                        spec,
+                        Some(establisher),
+                        open_handler,
+                        &registry,
+                        auth.clone(),
+                        None,
+                    )
+                    .expect("register_openable_with_establisher");
+                    let registry = Arc::new(registry);
+                    let provider: Arc<dyn IdentityProvider> = Arc::new(NoopIdProvider);
+                    let call_connection = Arc::new(CallConnection::new_single_stream(
+                        channel0_conn,
+                        Arc::clone(&writer),
+                    ));
+                    let dp = Dispatcher::new(registry, provider);
+                    dp.run_loop_single_stream(call_connection, reader, writer)
+                        .await;
+                })
+            });
+
+        let (client_end, server_end) = tokio::io::duplex(64 * 1024);
+        let client_conn =
+            Connection::from_bidi(client_end, b"alk/channels".to_vec(), Some(TEST_ADDR));
+        let server_conn =
+            Connection::from_bidi(server_end, b"alk/channels".to_vec(), Some(TEST_ADDR));
+
+        let adapter = ChannelsAdapter::new(install_hook, Arc::new(NoCap));
+        let auth = AuthContext::anonymous(b"alk/channels");
+        let _server_handle = tokio::spawn(async move {
+            let _ = crate::core::types::ProtocolHandler::handle(&adapter, server_conn, &auth).await;
+        });
+
+        let client = ChannelClient::from_connection(client_conn)
+            .await
+            .expect("channel client init");
+
+        let (channel_id, mut send, _recv) = client
+            .open_channel(
+                "channels/tty/sub",
+                serde_json::json!({ "container": "abc" }),
+                "alk/tty",
+            )
+            .await
+            .expect("open_channel with establisher success");
+
+        assert!(channel_id > 0, "channel_id should be non-zero");
+        send.write_all(b"ping").await.expect("write ping");
+        drop(send);
+
+        let data = tokio::time::timeout(std::time::Duration::from_secs(5), data_rx.recv())
+            .await
+            .expect("timed out waiting for handler data")
+            .expect("handler should receive data");
+        assert_eq!(&data, b"ping", "handler received ping post-establishment");
+    }
+
    // --- review 004 Unit 3 acceptance gates (F-04 serving half) -----------

    /// F-04 gate 1: hub→consumer call over an existing `ChannelClient`
@@ -108,6 +108,16 @@ struct Inner {
 /// the open-op response/first-data race). A channel whose adopter never
 /// arrives leaks its parked chunks until `clear_all`; the cap bounds
 /// that leak per channel.
+///
+/// Consumer-facing bound (review 006 E-04): for a push-first producer
+/// (dial-then-pump is the common tunnel shape), up to `EARLY_ARRIVAL_CAP`
+/// chunks per channel can be parked before the consumer's
+/// `adopt_channel` runs — and chunks past the cap drop silently at the
+/// consumer (data loss presents as a truncated stream with clean
+/// framing elsewhere; `dropped_unknown_chunks` /
+/// `early_arrival_count` are the producer-side observability). A
+/// tunnel crate's sizing (e.g. a UDP POC's MTU-vs-buffer math) should
+/// treat 64 parked chunks as the observable bound and adopt promptly.
 const EARLY_ARRIVAL_CAP: usize = 64;

 impl ChannelManager {
@@ -192,6 +202,19 @@ impl ChannelManager {
        self.inner.dropped_unknown_chunks.load(Ordering::Relaxed)
    }

+    /// The number of chunks parked in the early-arrival buffer since
+    /// the connection started (monotonic — parked chunks handed to the
+    /// adopter are not subtracted). Together with
+    /// [`Self::dropped_unknown_chunks`] this bounds the two observable
+    /// halves of the open-op-response/first-data race: how many of a
+    /// push-first producer's first chunks were buffered
+    /// (`early_arrival_count`) versus lost to the per-channel cap
+    /// (`dropped_unknown_chunks` — see `EARLY_ARRIVAL_CAP`, review 006
+    /// E-04). Observability only — neither counter drives control flow.
+    pub fn early_arrival_count(&self) -> u64 {
+        self.inner.early_arrival_count.load(Ordering::Relaxed)
+    }
+
    /// The mux handle — for registering new channels' write halves.
    pub fn mux(&self) -> &MuxHandle {
        &self.inner.mux
@@ -712,6 +735,42 @@ mod tests {
        );
    }

+    /// `early_arrival_count` observes parked chunks (review 006 N-2 —
+    /// the counter was write-only before the accessor). Monotonic by
+    /// design: it counts chunks parked since connection start; draining
+    /// on adopt does not subtract (paired with `dropped_unknown_chunks`
+    /// it bounds the open-response/first-data race's two halves).
+    #[tokio::test]
+    async fn early_arrival_count_tracks_parked_chunks_monotonically() {
+        let manager = make_manager_with_runner().await;
+        assert_eq!(manager.early_arrival_count(), 0);
+        for _ in 0..3 {
+            manager
+                .route_payload(7, Bytes::from_static(b"parked"))
+                .await;
+        }
+        assert_eq!(
+            manager.early_arrival_count(),
+            3,
+            "each parked chunk increments the counter"
+        );
+        // Adoption drains the buffer into the receiver but does not
+        // decrement (the accessor is an observability counter, not a
+        // live-depth gauge).
+        let (_send, mut recv) = manager
+            .adopt_channel(7, "alk/tty", None)
+            .await
+            .expect("adopt");
+        assert_eq!(
+            manager.early_arrival_count(),
+            3,
+            "adopt-drain does not decrement the monotonic counter"
+        );
+        use tokio::io::AsyncReadExt;
+        let mut buf = [0u8; 6 * 3];
+        recv.read_exact(&mut buf).await.expect("read parked chunks");
+    }
+
    #[tokio::test]
    async fn route_payload_to_known_channel_does_not_increment_dropped_counter() {
        let manager = make_manager_with_runner().await;
@@ -14,7 +14,9 @@
 //! See `docs/architecture/channel-operations.md` for the spec.

 use std::sync::Arc;
+use std::time::{Duration, Instant};

+use futures::future::BoxFuture;
 use serde_json::{json, Value};

 use crate::core::auth::{AuthContext, Identity};
@@ -295,7 +297,10 @@ fn make_resources_subscribe_handler(manager: ChannelManager) -> StreamingHandler
 }

 /// `ChannelCore` — the channel machinery the ALPN crate's open-op
-/// wrapper uses (ADR-047 §3). Provides [`ChannelCore::register_openable`],
+/// wrapper uses (ADR-047 §3, as amended by ADR-049 — the wrapper
+/// gains an awaited, bounded establishment phase via
+/// [`ChannelCore::register_openable_with_establisher`]). Provides
+/// [`ChannelCore::register_openable`],
 /// which wraps the ALPN's open handler with channel-id allocation,
 /// `ChannelManager` integration, opener-ledger recording,
 /// `ChannelLifecyclePolicy` consultation, and teardown hooks.
@@ -333,6 +338,85 @@ pub struct ChannelCore {
 pub type OpenHandler =
    Arc<dyn Fn(Value, Connection, AuthContext) -> tokio::task::JoinHandle<()> + Send + Sync>;

+/// The establishment-phase result (ADR-049 §1). Reserved for a channel
+/// plan — today the wrapper consults only success/failure, so `()`
+/// carries no data.
+#[derive(Debug, Clone, Default)]
+pub struct Establishment {}
+
+/// The establishment-failure reason code the wrapper puts in the open
+/// reply's `details.reason` (ADR-049 §3). The vocabulary maps 1:1 onto
+/// what an establisher can actually produce (per the SSH four;
+/// review 006's survey) plus the wrapper's own deadline.
+#[derive(Debug, Clone, PartialEq, Eq, thiserror::Error)]
+pub enum EstablishmentError {
+    /// The backend/target could not be reached or refused the
+    /// connection.
+    #[error("dial failed: {message}")]
+    DialFailed { message: String },
+    /// The requested resource does not exist.
+    #[error("unknown resource: {message}")]
+    UnknownResource { message: String },
+    /// The backend is out of capacity (ports, fds, slots).
+    #[error("resource shortage: {message}")]
+    ResourceShortage { message: String },
+    /// Establisher-internal failure not covered above.
+    #[error("handler error: {message}")]
+    HandlerError { message: String },
+}
+
+impl EstablishmentError {
+    /// The wire-visible reason code (`details.reason` in
+    /// `channel:open_failed`).
+    pub fn reason(&self) -> &'static str {
+        match self {
+            EstablishmentError::DialFailed { .. } => "dial_failed",
+            EstablishmentError::UnknownResource { .. } => "unknown_resource",
+            EstablishmentError::ResourceShortage { .. } => "resource_shortage",
+            EstablishmentError::HandlerError { .. } => "handler_error",
+        }
+    }
+
+    /// The human-readable detail message.
+    pub fn message(&self) -> &str {
+        match self {
+            EstablishmentError::DialFailed { message }
+            | EstablishmentError::UnknownResource { message }
+            | EstablishmentError::ResourceShortage { message }
+            | EstablishmentError::HandlerError { message } => message,
+        }
+    }
+}
+
+/// The establisher hook (ADR-049 §1): the awaited establishment phase
+/// of a channel open — validate params semantically, consult ownership,
+/// prepare/dial the backend. **Awaited by the open-op wrapper,
+/// bounded** (dispatch deadline or `ESTABLISHMENT_TIMEOUT`, whichever
+/// is earlier) — before the reply is written, before the pump handler
+/// is spawned. On failure the wrapper tears down the just-allocated
+/// channel and replies `channel:open_failed` with `details.reason`.
+///
+/// The establisher takes the open op's `input` (params) and the peer's
+/// `AuthContext`. It deliberately does **not** receive the channel's
+/// `Connection`: the channel `BiStream` is yield-once
+/// (`ChannelBidiStreamSource`) and belongs exclusively to the pump
+/// handler (the `OpenHandler`); the establisher is pre-data-plane (its
+/// dial targets the backend, not the channel). Amendment to the
+/// ADR-049 §1 signature sketch.
+pub type OpenEstablisher = Arc<
+    dyn Fn(Value, AuthContext) -> BoxFuture<'static, Result<Establishment, EstablishmentError>>
+        + Send
+        + Sync,
+>;
+
+/// The default bound on the establisher await (ADR-049 §2) when the
+/// `OperationContext` carries no deadline and the registration set no
+/// override.
+pub const ESTABLISHMENT_TIMEOUT: Duration = Duration::from_secs(10);
+
+/// The wire-visible error code for establishment failure (ADR-049 §3).
+pub const CHANNEL_OPEN_FAILED: &str = "channel:open_failed";
+
 /// The error code prefix for channel-open failures (ADR-047 §3). The
 /// wrapper maps `ChannelError` / `ManagerError` to `CallError` with
 /// codes prefixed by `channel:` so the initiator can branch on the
@@ -374,10 +458,17 @@ impl ChannelCore {
    /// spawn the protocol on the channel's `BiStream`). This wrapper
    /// does the channel machinery: ACL check (run by the registry's
    /// `invoke`/`invoke_streaming`/`invoke_sink` before the wrapper) →
-    /// `check_open(identity)` → `manager.open_channel(alpn, opener)`
-    /// → spawn the ALPN handler on the channel's `Connection` →
+    /// `check_open(identity)` → `manager.open_channel(alpn, opener)` →
+    /// spawn the ALPN handler on the channel's `Connection` →
    /// respond with `{ "channel_id": <id> }`.
    ///
+    /// **No establisher**: the open op cannot fail after allocation —
+    /// establishment work inside the handler is invisible to the open
+    /// reply (review 006 E-01's subject). Use
+    /// [`ChannelCore::register_openable_with_establisher`] when the
+    /// establishment phase can fail and the failure belongs in the
+    /// open reply (ADR-049).
+    ///
    /// The op is registered on the given `registry` (the connection
    /// overlay registry, Layer 2 per ADR-019 — this is the
    /// per-connection registration the §4 amendment blesses). The
@@ -402,6 +493,38 @@ impl ChannelCore {
        open_handler: OpenHandler,
        registry: &OperationRegistry,
        auth: AuthContext,
+    ) -> Result<(), String> {
+        self.register_openable_with_establisher(spec, None, open_handler, registry, auth, None)
+    }
+
+    /// Register a per-ALPN open op with an establishment phase
+    /// (ADR-049 §1/§5). The `establisher` is **awaited by the wrapper,
+    /// bounded** — after allocation, before the reply and before the
+    /// pump handler is spawned. On establisher failure (error or
+    /// deadline) the wrapper tears down the just-allocated channel and
+    /// replies `channel:open_failed` with
+    /// `details: { reason, message }`; on success the pump handler is
+    /// spawned exactly as [`ChannelCore::register_openable`] does.
+    ///
+    /// `timeout` bounds the establisher when the dispatch carries no
+    /// deadline (`None` = [`ESTABLISHMENT_TIMEOUT`], 10s). When the
+    /// `OperationContext` carries a deadline, the effective bound is
+    /// the earlier of the two (ADR-049 §2). The bound applies only to
+    /// the establisher — the spawned pump's lifetime is governed by
+    /// the existing teardown machinery, unchanged.
+    ///
+    /// Backward compatible by construction: `establisher: None` behaves
+    /// exactly like [`ChannelCore::register_openable`] (the
+    /// no-establisher shape), and existing `OpenHandler`s compile
+    /// unchanged.
+    pub fn register_openable_with_establisher(
+        &self,
+        spec: OperationSpec,
+        establisher: Option<OpenEstablisher>,
+        open_handler: OpenHandler,
+        registry: &OperationRegistry,
+        auth: AuthContext,
+        timeout: Option<Duration>,
    ) -> Result<(), String> {
        let op_type = spec.op_type;
        let channel_open = spec.channel_open.clone();
@@ -417,17 +540,22 @@ impl ChannelCore {
            .alpn
            .to_string();

+        let establisher = establisher.map(|establisher| EstablisherHook {
+            establisher,
+            timeout,
+        });
        let manager = self.manager.clone();
        let policy = Arc::clone(&self.policy);
        let open_handler = Arc::clone(&open_handler);

        let handler_kind = match op_type {
            OperationType::Query | OperationType::Mutation => HandlerKind::Once(
-                make_open_handler_once(manager, policy, open_handler, auth, alpn),
+                make_open_handler_once(manager, policy, establisher, open_handler, auth, alpn),
            ),
            OperationType::Sub => HandlerKind::Stream(make_open_handler_stream(
                manager,
                policy,
+                establisher,
                open_handler,
                auth,
                alpn,
@@ -435,6 +563,7 @@ impl ChannelCore {
            OperationType::Pub => HandlerKind::Sink(make_open_handler_sink(
                manager,
                policy,
+                establisher,
                open_handler,
                auth,
                alpn,
@@ -467,22 +596,103 @@ fn opener_identity_from_context(ctx: &OperationContext) -> Identity {
    })
 }

+/// The establisher hook + its per-registration bound override,
+/// threaded from `ChannelCore::register_openable_with_establisher`
+/// into the wrapper factories. `timeout: None` = `ESTABLISHMENT_TIMEOUT`.
+#[derive(Clone)]
+struct EstablisherHook {
+    establisher: OpenEstablisher,
+    timeout: Option<Duration>,
+}
+
+/// The effective bound on the establisher await (ADR-049 §2): the
+/// earlier of the dispatch deadline (when the `OperationContext`
+/// carries one) and the establishment timeout (the per-registration
+/// override, else `ESTABLISHMENT_TIMEOUT`). A deadline already in the
+/// past yields a zero bound — the timeout fires immediately.
+fn establishment_bound(timeout_override: Option<Duration>, deadline: Option<Instant>) -> Duration {
+    let timeout = timeout_override.unwrap_or(ESTABLISHMENT_TIMEOUT);
+    deadline
+        .map(|d| d.saturating_duration_since(Instant::now()).min(timeout))
+        .unwrap_or(timeout)
+}
+
+/// Tear down a just-allocated channel after establishment failure
+/// (ADR-049 §3): drop the demux sender (EOF to nothing — no handler
+/// was ever spawned), take the opener-ledger entry, and un-reserve the
+/// per-identity count (`policy.on_close` — the same un-increment path
+/// the allocation-failure arms run; the ledger `take` is the atomic
+/// gate, ADR-047 §7).
+fn teardown_failed_channel(
+    manager: &ChannelManager,
+    policy: &Arc<dyn ChannelLifecyclePolicy>,
+    channel_id: u32,
+    opener: &Identity,
+) {
+    if let Err(e) = manager.teardown_channel(channel_id) {
+        tracing::debug!(
+            channel_id,
+            error = %e,
+            "open wrapper: establisher-failure teardown found no channel to remove"
+        );
+    }
+    if manager.opener_ledger().take(channel_id).is_some() {
+        policy.on_close(opener);
+    }
+}
+
+/// The `channel:open_failed` reply for an establisher error
+/// (ADR-049 §3): `details` carries the reason code + message.
+fn establishment_error_to_call_error(err: &EstablishmentError) -> CallError {
+    CallError::new(
+        CHANNEL_OPEN_FAILED,
+        format!("channel establishment failed: {}", err.message()),
+        false,
+    )
+    .with_details(json!({ "reason": err.reason(), "message": err.message() }))
+}
+
+/// The `channel:open_failed` reply for a deadline expiry — same
+/// `details` shape, reason `timeout`.
+fn establishment_timeout_call_error() -> CallError {
+    CallError::new(
+        CHANNEL_OPEN_FAILED,
+        "channel establishment exceeded the deadline",
+        false,
+    )
+    .with_details(json!({
+        "reason": "timeout",
+        "message": "establishment exceeded the deadline",
+    }))
+}
+
 /// Run the open-op wrapper's shared post-ACL steps: `check_open` →
-/// `open_channel` → build the channel `Connection` → spawn the ALPN
-/// handler → return `{ channel_id }` on success, or a `CallError` on
-/// any failure. The ACL check has already run (by the registry's
-/// `invoke`/`invoke_streaming`/`invoke_sink` before the wrapper); this
-/// function is the `check_open` → `allocate` → `ledger` → `spawn` →
-/// `respond` tail of the ADR-047 §3 flow.
+/// `open_channel` → **await the establisher bounded** (ADR-049 §1/§2 —
+/// no-op when no establisher is registered) → build the channel
+/// `Connection` → spawn the ALPN handler → return `{ channel_id }` on
+/// success, or a `CallError` on any failure. The ACL check has already
+/// run (by the registry's `invoke`/`invoke_streaming`/`invoke_sink`
+/// before the wrapper); this function is the `check_open` →
+/// `allocate` → `establish` → `ledger` → `spawn` → `respond` tail of
+/// the ADR-047 §3 flow (as amended by ADR-049).
+///
+/// On establishment failure (error or deadline) the wrapper tears down
+/// the just-allocated channel (demux sender, opener-ledger entry,
+/// `policy.on_close` un-increment) and replies `channel:open_failed`
+/// with `details: { reason, message }` — the SSH "channel never exists
+/// opener-side" property: the consumer's open resolves `Err` and no
+/// `channel_id` was ever returned.
 ///
 /// `input` is the open op's input (params), passed through to the
-/// ALPN's `OpenHandler` so it can validate params and prepare the
-/// backend. `opener_id` is the `PeerId` recorded in the opener ledger
-/// (the direct caller's identity id).
+/// establisher (when registered) and the ALPN's `OpenHandler`.
+/// `opener_id` is the `PeerId` recorded in the opener ledger (the
+/// direct caller's identity id). `opener_identity` is the identity the
+/// cap was reserved against (un-reserved on failure paths).
 #[allow(clippy::too_many_arguments)]
 async fn run_open_wrapper(
    manager: &ChannelManager,
    policy: &Arc<dyn ChannelLifecyclePolicy>,
+    establisher: Option<&EstablisherHook>,
    open_handler: &OpenHandler,
    auth: &AuthContext,
    alpn: &str,
@@ -490,6 +700,7 @@ async fn run_open_wrapper(
    opener_id: String,
    opener_identity: Identity,
    request_id: String,
+    deadline: Option<Instant>,
 ) -> ResponseEnvelope {
    if let Err(channel_err) = policy.check_open(&opener_identity) {
        return ResponseEnvelope::error(request_id, map_channel_error_to_call_error(&channel_err));
@@ -497,6 +708,39 @@ async fn run_open_wrapper(

    let channel_id = match manager.open_channel(alpn, opener_id, None).await {
        Ok((id, send, recv)) => {
+            // The establishment phase (ADR-049 §1): awaited bounded,
+            // before the reply and before the pump handler is spawned.
+            // No establisher registered = an always-OK establisher
+            // (the pre-ADR-049 shape, unchanged).
+            if let Some(hook) = establisher {
+                let bound = establishment_bound(hook.timeout, deadline);
+                let establishment =
+                    tokio::time::timeout(bound, (hook.establisher)(input.clone(), auth.clone()))
+                        .await;
+                match establishment {
+                    Err(_elapsed) => {
+                        teardown_failed_channel(manager, policy, id, &opener_identity);
+                        return ResponseEnvelope::error(
+                            request_id,
+                            establishment_timeout_call_error(),
+                        );
+                    }
+                    Ok(Err(e)) => {
+                        tracing::debug!(
+                            channel_id = id,
+                            reason = e.reason(),
+                            "open wrapper: establisher failed; tearing down channel"
+                        );
+                        teardown_failed_channel(manager, policy, id, &opener_identity);
+                        return ResponseEnvelope::error(
+                            request_id,
+                            establishment_error_to_call_error(&e),
+                        );
+                    }
+                    Ok(Ok(_establishment)) => {}
+                }
+            }
+
            let remote_addr = manager.remote_addr();
            let source = super::source::channel_source(recv, send, remote_addr);
            let channel_conn = Connection::from_source(source, alpn.as_bytes().to_vec());
@@ -506,7 +750,23 @@ async fn run_open_wrapper(
            let teardown_policy = Arc::clone(policy);
            let task = tokio::spawn(async move {
                let _ = raw_task.await;
-                let _ = teardown_manager.teardown_channel(id);
+                // Benign-race pin (review 006 E-03): `channel/close`'s
+                // awaited teardown and this handler-exit teardown both
+                // gate on the atomic `opener_ledger().take(id)`, so the
+                // loser of the race gets `UnknownChannel` here and skips
+                // the ledger/policy half — no double-decrement. A
+                // vanished-after-install channel (transport EOF
+                // `clear_all`) is equally benign: `clear_all` drained
+                // the ledger and decremented the policy itself. The
+                // vanished-between-open-and-install case surfaces as the
+                // `set_handler_task` warn below.
+                if let Err(e) = teardown_manager.teardown_channel(id) {
+                    tracing::debug!(
+                        channel_id = id,
+                        error = %e,
+                        "open wrapper: handler-exit teardown found no channel to remove (benign when racing channel/close)"
+                    );
+                }
                if let Some(opener_id) = teardown_manager.opener_ledger().take(id) {
                    let opener = Identity {
                        id: opener_id,
@@ -584,6 +844,7 @@ fn map_channel_error_to_call_error(err: &ChannelError) -> CallError {
 fn make_open_handler_once(
    manager: ChannelManager,
    policy: Arc<dyn ChannelLifecyclePolicy>,
+    establisher: Option<EstablisherHook>,
    open_handler: OpenHandler,
    auth: AuthContext,
    alpn: String,
@@ -591,6 +852,7 @@ fn make_open_handler_once(
    Arc::new(move |input: Value, ctx: OperationContext| {
        let manager = manager.clone();
        let policy = Arc::clone(&policy);
+        let establisher = establisher.clone();
        let open_handler = Arc::clone(&open_handler);
        let auth = auth.clone();
        let alpn = alpn.clone();
@@ -601,6 +863,7 @@ fn make_open_handler_once(
            run_open_wrapper(
                &manager,
                &policy,
+                establisher.as_ref(),
                &open_handler,
                &auth,
                &alpn,
@@ -608,6 +871,7 @@ fn make_open_handler_once(
                opener_id,
                opener_identity,
                request_id,
+                ctx.deadline,
            )
            .await
        })
@@ -625,6 +889,7 @@ fn make_open_handler_once(
 fn make_open_handler_stream(
    manager: ChannelManager,
    policy: Arc<dyn ChannelLifecyclePolicy>,
+    establisher: Option<EstablisherHook>,
    open_handler: OpenHandler,
    auth: AuthContext,
    alpn: String,
@@ -632,6 +897,7 @@ fn make_open_handler_stream(
    Arc::new(move |input: Value, ctx: OperationContext| {
        let manager = manager.clone();
        let policy = Arc::clone(&policy);
+        let establisher = establisher.clone();
        let open_handler = Arc::clone(&open_handler);
        let auth = auth.clone();
        let alpn = alpn.clone();
@@ -642,6 +908,7 @@ fn make_open_handler_stream(
            run_open_wrapper(
                &manager,
                &policy,
+                establisher.as_ref(),
                &open_handler,
                &auth,
                &alpn,
@@ -649,6 +916,7 @@ fn make_open_handler_stream(
                opener_id,
                opener_identity,
                request_id,
+                ctx.deadline,
            )
            .await
        }))
@@ -675,6 +943,7 @@ fn make_open_handler_stream(
 fn make_open_handler_sink(
    _manager: ChannelManager,
    _policy: Arc<dyn ChannelLifecyclePolicy>,
+    _establisher: Option<EstablisherHook>,
    _open_handler: OpenHandler,
    _auth: AuthContext,
    _alpn: String,
@@ -1039,6 +1308,7 @@ mod tests {
        let handler = make_open_handler_once(
            manager.clone(),
            policy,
+            None,
            open_handler,
            auth,
            "alk/tty".to_string(),
@@ -1069,6 +1339,7 @@ mod tests {
        let handler = make_open_handler_stream(
            manager.clone(),
            policy,
+            None,
            open_handler,
            auth,
            "alk/tty".to_string(),
@@ -1096,8 +1367,14 @@ mod tests {
        let policy = super::super::policy::default_policy();
        let open_handler: OpenHandler = Arc::new(|_input, _conn, _auth| tokio::spawn(async {}));
        let auth = AuthContext::anonymous(b"alk/call");
-        let handler =
-            make_open_handler_sink(manager, policy, open_handler, auth, "alk/tty".to_string());
+        let handler = make_open_handler_sink(
+            manager,
+            policy,
+            None,
+            open_handler,
+            auth,
+            "alk/tty".to_string(),
+        );
        let publish_stream: crate::registry::registration::PublishStream =
            Box::pin(futures::stream::empty());
        let env = handler(json!({}), test_context("open-sink-1"), publish_stream).await;
@@ -1265,6 +1542,7 @@ mod tests {
        let env = run_open_wrapper(
            &manager,
            &policy,
+            None,
            &open_handler,
            &auth,
            "alk/tty",
@@ -1272,6 +1550,7 @@ mod tests {
            opener_id.id.clone(),
            opener_id,
            "req-cap-deny".to_string(),
+            None,
        )
        .await;
        match env.result {
@@ -1279,4 +1558,368 @@ mod tests {
            Ok(_) => panic!("cap 0 should deny open"),
        }
    }
+
+    // --- ADR-049 Unit 1: the establishment phase -------------------------
+
+    fn failing_establisher() -> OpenEstablisher {
+        Arc::new(|_input, _auth| {
+            Box::pin(async {
+                Err(EstablishmentError::DialFailed {
+                    message: "connection refused".to_string(),
+                })
+            })
+        })
+    }
+
+    fn ok_establisher() -> OpenEstablisher {
+        Arc::new(|_input, _auth| Box::pin(async { Ok(Establishment::default()) }))
+    }
+
+    fn hook(establisher: OpenEstablisher, timeout: Option<Duration>) -> Option<EstablisherHook> {
+        Some(EstablisherHook {
+            establisher,
+            timeout,
+        })
+    }
+
+    fn identity(id: &str) -> Identity {
+        Identity {
+            id: id.to_string(),
+            scopes: vec![],
+            resources: HashMap::new(),
+        }
+    }
+
+    #[tokio::test]
+    async fn run_open_wrapper_establisher_failure_tears_down_and_replies_open_failed() {
+        let manager = make_manager().await;
+        let concrete_policy = Arc::new(super::super::policy::PerIdentityChannelPolicy::new(8));
+        let policy: Arc<dyn ChannelLifecyclePolicy> =
+            Arc::clone(&concrete_policy) as Arc<dyn ChannelLifecyclePolicy>;
+        let spawned = Arc::new(AtomicBool::new(false));
+        let spawned_clone = Arc::clone(&spawned);
+        let open_handler: OpenHandler = Arc::new(move |_input, _conn, _auth| {
+            spawned_clone.store(true, Ordering::SeqCst);
+            tokio::spawn(async {})
+        });
+        let auth = AuthContext::anonymous(b"alk/call");
+        let env = run_open_wrapper(
+            &manager,
+            &policy,
+            hook(failing_establisher(), None).as_ref(),
+            &open_handler,
+            &auth,
+            "alk/tty",
+            json!({}),
+            "alice".to_string(),
+            identity("alice"),
+            "req-est-fail".to_string(),
+            None,
+        )
+        .await;
+        match env.result {
+            Err(e) => {
+                assert_eq!(e.code, "channel:open_failed");
+                assert!(!e.retryable);
+                let details = e.details.expect("details carry the reason");
+                assert_eq!(details["reason"], "dial_failed");
+                assert_eq!(details["message"], "connection refused");
+            }
+            Ok(_) => panic!("establisher failure must fail the open"),
+        }
+        // The SSH "channel never exists opener-side" property: the
+        // channel was torn down and no `channel_id` was ever returned.
+        assert!(
+            manager.channel_ids().is_empty(),
+            "no channel survives a failed establishment"
+        );
+        assert_eq!(manager.open_count(), 0);
+        // The per-identity cap reservation was un-incremented.
+        assert_eq!(
+            concrete_policy.count_for(&identity("alice")),
+            0,
+            "ledger take + policy.on_close restored the cap count"
+        );
+        // The pump handler was never spawned.
+        assert!(
+            !spawned.load(Ordering::SeqCst),
+            "pump handler must not spawn on establishment failure"
+        );
+    }
+
+    #[tokio::test]
+    async fn run_open_wrapper_establisher_timeout_replies_timeout_reason() {
+        let manager = make_manager().await;
+        let concrete_policy = Arc::new(super::super::policy::PerIdentityChannelPolicy::new(8));
+        let policy: Arc<dyn ChannelLifecyclePolicy> =
+            Arc::clone(&concrete_policy) as Arc<dyn ChannelLifecyclePolicy>;
+        let open_handler: OpenHandler = Arc::new(|_input, _conn, _auth| tokio::spawn(async {}));
+        let auth = AuthContext::anonymous(b"alk/call");
+        let hanging: OpenEstablisher = Arc::new(|_input, _auth| {
+            Box::pin(async {
+                tokio::time::sleep(Duration::from_secs(5)).await;
+                Ok(Establishment::default())
+            })
+        });
+        let env = run_open_wrapper(
+            &manager,
+            &policy,
+            hook(hanging, Some(Duration::from_millis(50))).as_ref(),
+            &open_handler,
+            &auth,
+            "alk/tty",
+            json!({}),
+            "alice".to_string(),
+            identity("alice"),
+            "req-est-timeout".to_string(),
+            None,
+        )
+        .await;
+        match env.result {
+            Err(e) => {
+                assert_eq!(e.code, "channel:open_failed");
+                let details = e.details.expect("details carry the reason");
+                assert_eq!(details["reason"], "timeout");
+            }
+            Ok(_) => panic!("a hung establisher must fail the open within the bound"),
+        }
+        assert!(manager.channel_ids().is_empty(), "channel torn down");
+        assert_eq!(
+            concrete_policy.count_for(&identity("alice")),
+            0,
+            "ledger decremented on timeout"
+        );
+    }
+
+    #[tokio::test]
+    async fn run_open_wrapper_dispatch_deadline_bounds_establisher() {
+        let manager = make_manager().await;
+        let policy = super::super::policy::default_policy();
+        let open_handler: OpenHandler = Arc::new(|_input, _conn, _auth| tokio::spawn(async {}));
+        let auth = AuthContext::anonymous(b"alk/call");
+        let hanging: OpenEstablisher = Arc::new(|_input, _auth| {
+            Box::pin(async {
+                tokio::time::sleep(Duration::from_secs(5)).await;
+                Ok(Establishment::default())
+            })
+        });
+        // No per-registration override; the dispatch deadline (50ms) is
+        // the bound — the earlier of the two per ADR-049 §2.
+        let env = run_open_wrapper(
+            &manager,
+            &policy,
+            hook(hanging, None).as_ref(),
+            &open_handler,
+            &auth,
+            "alk/tty",
+            json!({}),
+            "alice".to_string(),
+            identity("alice"),
+            "req-est-deadline".to_string(),
+            Some(Instant::now() + Duration::from_millis(50)),
+        )
+        .await;
+        match env.result {
+            Err(e) => {
+                assert_eq!(e.code, "channel:open_failed");
+                assert_eq!(e.details.as_ref().expect("details")["reason"], "timeout");
+            }
+            Ok(_) => panic!("deadline must bound the establisher"),
+        }
+        assert!(manager.channel_ids().is_empty());
+    }
+
+    #[tokio::test]
+    async fn run_open_wrapper_establisher_success_spawns_pumps_and_replies_channel_id() {
+        let manager = make_manager().await;
+        let policy = super::super::policy::default_policy();
+        let spawned = Arc::new(AtomicBool::new(false));
+        let spawned_clone = Arc::clone(&spawned);
+        let open_handler: OpenHandler = Arc::new(move |_input, _conn, _auth| {
+            spawned_clone.store(true, Ordering::SeqCst);
+            tokio::spawn(async {})
+        });
+        let auth = AuthContext::anonymous(b"alk/call");
+        let env = run_open_wrapper(
+            &manager,
+            &policy,
+            hook(ok_establisher(), None).as_ref(),
+            &open_handler,
+            &auth,
+            "alk/tty",
+            json!({}),
+            "alice".to_string(),
+            identity("alice"),
+            "req-est-ok".to_string(),
+            None,
+        )
+        .await;
+        match env.result {
+            Ok(v) => {
+                let channel_id = v["channel_id"].as_u64().expect("channel_id");
+                assert!(channel_id > 0);
+                assert!(manager.has_channel(channel_id as u32));
+            }
+            Err(e) => panic!("successful establishment should open, got: {e:?}"),
+        }
+        assert!(spawned.load(Ordering::SeqCst));
+    }
+
+    #[test]
+    fn establishment_error_reason_mapping_covers_the_vocabulary() {
+        let cases: Vec<(EstablishmentError, &str)> = vec![
+            (
+                EstablishmentError::DialFailed {
+                    message: "refused".into(),
+                },
+                "dial_failed",
+            ),
+            (
+                EstablishmentError::UnknownResource {
+                    message: "gone".into(),
+                },
+                "unknown_resource",
+            ),
+            (
+                EstablishmentError::ResourceShortage {
+                    message: "no fds".into(),
+                },
+                "resource_shortage",
+            ),
+            (
+                EstablishmentError::HandlerError {
+                    message: "boom".into(),
+                },
+                "handler_error",
+            ),
+        ];
+        for (err, reason) in cases {
+            let call_err = establishment_error_to_call_error(&err);
+            assert_eq!(call_err.code, "channel:open_failed");
+            let details = call_err.details.expect("details");
+            assert_eq!(details["reason"], reason);
+            assert_eq!(details["message"], err.message());
+        }
+    }
+
+    #[test]
+    fn establishment_timeout_error_carries_timeout_reason() {
+        let err = establishment_timeout_call_error();
+        assert_eq!(err.code, "channel:open_failed");
+        assert_eq!(err.details.as_ref().expect("details")["reason"], "timeout");
+    }
+
+    #[test]
+    fn establishment_bound_is_the_earlier_of_deadline_and_timeout() {
+        // No deadline → the override (or the 10s default).
+        assert_eq!(establishment_bound(None, None), ESTABLISHMENT_TIMEOUT);
+        assert_eq!(
+            establishment_bound(Some(Duration::from_secs(3)), None),
+            Duration::from_secs(3)
+        );
+        // Deadline earlier than the timeout → the deadline.
+        let soon = Instant::now() + Duration::from_millis(100);
+        let bound = establishment_bound(None, Some(soon));
+        assert!(bound <= Duration::from_millis(100));
+        // Deadline later than the timeout → the timeout wins.
+        let late = Instant::now() + Duration::from_secs(60);
+        assert_eq!(
+            establishment_bound(Some(Duration::from_secs(3)), Some(late)),
+            Duration::from_secs(3)
+        );
+        // Deadline already past → zero bound (timeout fires immediately).
+        let past = Instant::now() - Duration::from_secs(1);
+        assert_eq!(establishment_bound(None, Some(past)), Duration::ZERO);
+    }
+
+    #[tokio::test]
+    async fn register_openable_with_establisher_fails_via_invoke_streaming() {
+        let manager = make_manager().await;
+        let concrete_policy = Arc::new(super::super::policy::PerIdentityChannelPolicy::new(8));
+        let policy: Arc<dyn ChannelLifecyclePolicy> =
+            Arc::clone(&concrete_policy) as Arc<dyn ChannelLifecyclePolicy>;
+        let core = ChannelCore::new(manager.clone(), policy);
+        let spec = OperationSpec::new(
+            "channels/tty/sub",
+            OperationType::Sub,
+            Visibility::External,
+            json!({}),
+            json!({ "type": "object", "properties": { "channel_id": { "type": "integer" } } }),
+            vec![],
+            AccessControl::default(),
+            None,
+        )
+        .with_channel_open(ChannelOpenSpec::new("alk/tty"));
+        let open_handler: OpenHandler = Arc::new(|_input, _conn, _auth| tokio::spawn(async {}));
+        let registry = OperationRegistry::new();
+        core.register_openable_with_establisher(
+            spec,
+            Some(failing_establisher()),
+            open_handler,
+            &registry,
+            AuthContext::anonymous(b"alk/call"),
+            None,
+        )
+        .expect("register");
+        let mut stream =
+            registry.invoke_streaming("channels/tty/sub", json!({}), test_context("reg-est-fail"));
+        let env = stream.next().await.expect("one envelope");
+        match env.result {
+            Err(e) => {
+                assert_eq!(e.code, "channel:open_failed");
+                assert_eq!(
+                    e.details.as_ref().expect("details")["reason"],
+                    "dial_failed"
+                );
+            }
+            Ok(_) => panic!("establisher failure must surface as a call error"),
+        }
+        assert!(manager.channel_ids().is_empty());
+        assert_eq!(
+            concrete_policy.count_for(&identity("alice")),
+            0,
+            "no-establisher compat: registry-level failure un-reserves the ledger"
+        );
+    }
+
+    #[tokio::test]
+    async fn register_openable_no_establisher_behaves_as_today() {
+        let manager = make_manager().await;
+        let policy = super::super::policy::default_policy();
+        let core = ChannelCore::new(manager.clone(), policy);
+        let spec = OperationSpec::new(
+            "channels/tty/sub",
+            OperationType::Query,
+            Visibility::External,
+            json!({}),
+            json!({ "type": "object", "properties": { "channel_id": { "type": "integer" } } }),
+            vec![],
+            AccessControl::default(),
+            None,
+        )
+        .with_channel_open(ChannelOpenSpec::new("alk/tty"));
+        let spawned = Arc::new(AtomicBool::new(false));
+        let spawned_clone = Arc::clone(&spawned);
+        let open_handler: OpenHandler = Arc::new(move |_input, _conn, _auth| {
+            spawned_clone.store(true, Ordering::SeqCst);
+            tokio::spawn(async {})
+        });
+        let registry = OperationRegistry::new();
+        core.register_openable(
+            spec,
+            open_handler,
+            &registry,
+            AuthContext::anonymous(b"alk/call"),
+        )
+        .expect("register");
+        let env = registry
+            .invoke("channels/tty/sub", json!({}), test_context("reg-compat"))
+            .await;
+        match env.result {
+            Ok(v) => assert!(v["channel_id"].as_u64().is_some()),
+            Err(e) => panic!("no-establisher open should succeed, got: {e:?}"),
+        }
+        assert!(spawned.load(Ordering::SeqCst));
+        assert_eq!(manager.open_count(), 1, "channel stays open (compat)");
+    }
 }
@@ -285,6 +285,10 @@ pub(crate) fn rebuild_spec_for(
        }
    }

+    if let Some(description) = schema_json.get("description").and_then(|v| v.as_str()) {
+        spec = spec.with_description(description);
+    }
+
    Ok(spec)
 }

@@ -768,6 +772,64 @@ mod tests {
        assert_eq!(rebuilt.publish_schema.as_ref(), Some(&publish_schema));
    }

+    /// E-02 gate (review 006): `description` survives the spec wire
+    /// round-trip — `spec_to_json_pub` serializes it when set,
+    /// `rebuild_spec_for` parses it back (the `op/register` announced-spec
+    /// path and the `from_call` import path both parse through here).
+    #[test]
+    fn spec_round_trips_description() {
+        use crate::registry::discovery::spec_to_json_pub;
+
+        let spec = OperationSpec::new(
+            "channels/tty/sub",
+            OperationType::Sub,
+            Visibility::External,
+            json!({}),
+            json!({}),
+            vec![],
+            crate::registry::spec::AccessControl::default(),
+            None,
+        )
+        .with_description("Interactive TTY sessions");
+        let wire = spec_to_json_pub(&spec);
+        assert_eq!(
+            wire.get("description").and_then(|v| v.as_str()),
+            Some("Interactive TTY sessions"),
+            "description serialized"
+        );
+
+        let rebuilt = rebuild_spec_for(&wire, "channels/tty/sub", &None).expect("rebuild");
+        assert_eq!(
+            rebuilt.description.as_deref(),
+            Some("Interactive TTY sessions"),
+            "description survives the round-trip"
+        );
+    }
+
+    /// E-02 companion: a spec without `description` serializes no
+    /// `description` key and rebuilds with `None` (additive optional
+    /// field — absent stays absent, old producers stay parseable).
+    #[test]
+    fn spec_without_description_stays_absent_through_round_trip() {
+        use crate::registry::discovery::spec_to_json_pub;
+
+        let spec = OperationSpec::new(
+            "fs/readFile",
+            OperationType::Query,
+            Visibility::External,
+            json!({}),
+            json!({}),
+            vec![],
+            crate::registry::spec::AccessControl::default(),
+            None,
+        );
+        let wire = spec_to_json_pub(&spec);
+        assert!(wire.get("description").is_none());
+
+        let rebuilt = rebuild_spec_for(&wire, "fs/readFile", &None).expect("rebuild");
+        assert_eq!(rebuilt.description, None);
+    }
+
    #[test]
    fn derive_alpn_from_op_name_strips_channels_prefix() {
        assert_eq!(
@@ -33,6 +33,10 @@ pub fn services_list_spec() -> OperationSpec {
                            "op_type": {
                                "type": "string",
                                "enum": ["query", "mutation", "sub", "pub"]
+                            },
+                            "description": {
+                                "type": "string",
+                                "description": "Human-readable op description (review 006 E-02). Absent when the producer declares none."
                            }
                        }
                    }
@@ -87,6 +91,10 @@ pub fn services_list_peers_spec() -> OperationSpec {
                                        "op_type": {
                                            "type": "string",
                                            "enum": ["query", "mutation", "sub", "pub"]
+                                        },
+                                        "description": {
+                                            "type": "string",
+                                            "description": "Human-readable op description. Absent when the op declares none."
                                        }
                                    }
                                }
@@ -116,6 +124,9 @@ fn operation_spec_schema() -> Value {
                "type": "string",
                "enum": ["external", "internal"]
            },
+            "description": {
+                "description": "Human-readable op description (review 006 E-02). Absent when the op declares none; disclosed verbatim in `services/list` when set."
+            },
            "input_schema": {},
            "output_schema": {},
            "error_schemas": {
@@ -227,6 +238,9 @@ pub fn spec_to_json_pub(spec: &OperationSpec) -> Value {
    if let Some(resource_id_path) = &spec.resource_id_path {
        json["resource_id_path"] = json!(resource_id_path);
    }
+    if let Some(description) = &spec.description {
+        json["description"] = json!(description);
+    }
    if spec.channel_open.is_some() {
        json["channel_open"] = json!(true);
    }
@@ -259,11 +273,15 @@ pub fn services_list_handler(registry: Arc<OperationRegistry>) -> Handler {
                        .is_allowed()
                })
                .map(|s| {
-                    json!({
+                    let mut listing = json!({
                        "name": s.name,
                        "namespace": s.namespace,
                        "op_type": op_type_str(s.op_type),
-                    })
+                    });
+                    if let Some(description) = &s.description {
+                        listing["description"] = json!(description);
+                    }
+                    listing
                })
                .collect();
            ResponseEnvelope::ok(ctx.request_id, json!({ "operations": ops }))
@@ -333,11 +351,15 @@ pub fn services_list_peers_handler(registry: Arc<OperationRegistry>) -> Handler
                        .is_allowed()
                })
                .map(|s| {
-                    json!({
+                    let mut listing = json!({
                        "name": s.name,
                        "namespace": s.namespace,
                        "op_type": op_type_str(s.op_type),
-                    })
+                    });
+                    if let Some(description) = &s.description {
+                        listing["description"] = json!(description);
+                    }
+                    listing
                })
                .collect();
            let mut peers: Vec<Value> = Vec::new();
@@ -1057,6 +1079,106 @@ mod tests {
        );
    }

+    // --- review 006 E-02: `description` on OperationSpec -------------------
+
+    #[test]
+    fn spec_to_json_emits_description_when_set() {
+        let spec = external_spec("fs/readFile").with_description("Read a file");
+        let json_val = spec_to_json(&spec);
+        assert_eq!(json_val.get("description"), Some(&json!("Read a file")));
+    }
+
+    #[test]
+    fn spec_to_json_omits_description_when_absent() {
+        let spec = external_spec("fs/readFile");
+        let json_val = spec_to_json(&spec);
+        assert!(
+            json_val.get("description").is_none(),
+            "description must be absent when not set (additive optional field)"
+        );
+    }
+
+    #[tokio::test]
+    async fn services_list_emits_description_when_set() {
+        let registry = Arc::new(OperationRegistry::new());
+        registry
+            .register(HandlerRegistration::new(
+                external_spec("channels/tty/sub").with_description("Interactive TTY sessions"),
+                HandlerKind::Once(echo_handler()),
+                OperationProvenance::Local,
+                None,
+                None,
+                Capabilities::new(),
+            ))
+            .unwrap();
+        registry
+            .register(HandlerRegistration::new(
+                external_spec("fs/readFile"),
+                HandlerKind::Once(echo_handler()),
+                OperationProvenance::Local,
+                None,
+                None,
+                Capabilities::new(),
+            ))
+            .unwrap();
+        let handler = services_list_handler(Arc::clone(&registry));
+        let response = handler(json!({}), root_context("req-e02-1")).await;
+        let output = response.result.expect("ok response");
+        let ops = output
+            .get("operations")
+            .and_then(|v| v.as_array())
+            .expect("operations array")
+            .iter()
+            .map(|o| {
+                (
+                    o.get("name").and_then(|n| n.as_str()).unwrap_or(""),
+                    o.get("description").and_then(|d| d.as_str()),
+                )
+            })
+            .collect::<Vec<_>>();
+        assert!(
+            ops.contains(&("channels/tty/sub", Some("Interactive TTY sessions"))),
+            "described op carries its description: {ops:?}"
+        );
+        assert!(
+            ops.contains(&("fs/readFile", None)),
+            "undescribed op omits the description key: {ops:?}"
+        );
+    }
+
+    #[tokio::test]
+    async fn services_schema_discloses_description() {
+        let registry = registry_with_ops();
+        let handler = services_schema_handler(Arc::clone(&registry));
+        let described = external_spec("fs/readFile").with_description("Read a file");
+        registry
+            .register(HandlerRegistration::new(
+                described,
+                HandlerKind::Once(echo_handler()),
+                OperationProvenance::Local,
+                None,
+                None,
+                Capabilities::new(),
+            ))
+            .unwrap();
+        let response = handler(json!({ "name": "fs/readFile" }), root_context("req-e02-2")).await;
+        let spec = response.result.expect("ok response");
+        assert_eq!(spec.get("description"), Some(&json!("Read a file")));
+    }
+
+    #[test]
+    fn operation_spec_schema_documents_description_property() {
+        let schema = operation_spec_schema();
+        let props = schema
+            .get("properties")
+            .and_then(|v| v.as_object())
+            .expect("properties object");
+        assert!(
+            props.contains_key("description"),
+            "operation_spec_schema must advertise description"
+        );
+    }
+
    #[tokio::test]
    async fn services_list_filters_by_access_control_authorized_peer() {
        let registry = registry_with_access_controlled_ops();
@@ -181,6 +181,13 @@ pub struct OperationSpec {
    pub output_schema: Value,
    pub error_schemas: Vec<ErrorDefinition>,
    pub access_control: AccessControl,
+    /// Human-readable op description, disclosed by `services/list` when
+    /// set and by `services/schema` (`spec_to_json_pub`) — review 006
+    /// E-02. `None` (absent on the wire) for ops that declare none; the
+    /// field is additive and registry-side (it describes the op, not the
+    /// produced resource set — ADR-047 §6 keeps the live half of
+    /// discovery in `channel/resources/subscribe`).
+    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"`
@@ -234,12 +241,22 @@ impl OperationSpec {
            output_schema,
            error_schemas,
            access_control,
+            description: None,
            resource_id_path,
            publish_schema: None,
            channel_open: None,
        }
    }

+    /// Set the op's `description` (review 006 E-02). Disclosed by
+    /// `services/list` when set; carried in the `services/schema` wire
+    /// shape (`spec_to_json_pub` / `rebuild_spec_for`). Builder-style;
+    /// returns `self` for chaining at registration sites.
+    pub fn with_description(mut self, description: impl Into<String>) -> Self {
+        self.description = Some(description.into());
+        self
+    }
+
    /// Set the `publish_schema` (Pub ops only, ADR-046). Validates each
    /// `call.published` chunk's `input`. Builder-style; returns `self`
    /// for chaining at registration sites.
@@ -359,6 +376,27 @@ mod tests {
        assert_eq!(spec.channel_open, None);
    }

+    #[test]
+    fn description_defaults_to_none_and_builder_sets_it() {
+        let spec = OperationSpec::new(
+            "channels/tty/sub",
+            OperationType::Sub,
+            Visibility::External,
+            serde_json::json!({}),
+            serde_json::json!({}),
+            vec![],
+            AccessControl::default(),
+            None,
+        );
+        assert_eq!(spec.description, None);
+
+        let described = spec.with_description("Interactive TTY sessions");
+        assert_eq!(
+            described.description.as_deref(),
+            Some("Interactive TTY sessions")
+        );
+    }
+
    #[test]
    fn with_channel_open_sets_marker() {
        let spec = OperationSpec::new(
Author	SHA1	Message	Date
glm-5.3-flash	36e74cda11	feat(review 006 Unit 3): teardown-race log, early-arrival bound docs, count accessor (E-03, E-04, N-2) - E-03: the open wrapper's handler-exit teardown no longer discards UnknownChannel silently — debug log + benign-race pinning comment (ledger take is the atomic gate; no double-decrement) - E-04: consumer-facing doc note on the 64-parked-chunks observable bound (channel-client.md + EARLY_ARRIVAL_CAP const doc) for tunnel-style push-first producers - N-2: ChannelManager::early_arrival_count() accessor (the observability choice over removing the write-only counter), documented monotonic, with a park/adopt-drain monotonicity test - review 006: Unit 3 marked implemented in Status and remediation plan Verification: 617 tests pass; clippy -D warnings clean (host + wasm32 check); fmt clean; doc clean	2026-09-06 19:35:18 +00:00
glm-5.3-flash	f8dad9dbc8	feat(review 006 Unit 2): additive OperationSpec.description disclosed via discovery (E-02) - OperationSpec gains description: Option<String> (builder with_description, defaults None; no struct-literal construction sites exist, so additive by construction) - spec_to_json_pub emits description when set; rebuild_spec_for parses it back — the field survives from_call discovery and op/register announcement (same round-trip pattern as resource_id_path / publish_schema) - services/list and the local-ops half of services/list-peers emit description when set; output-schema docs on both listing specs and operation_spec_schema advertise the field - Tests: builder/default, emit/omit, listing emission, schema disclosure, schema-doc presence, round-trip + absent-stays-absent (8 new; 616 total) - Docs: review 006 Unit 2 marked IMPLEMENTED; ADR-047 §6 amendment records the E-02 discovery decision (listing enrichment lands, the channel/resources/subscribe half stays deferred); OQ-40 gains the load-bearing note; operation-registry.md struct + listing docs; CHANGELOG Verification: cargo test (616 pass), clippy -D warnings (host + wasm32), fmt --check, cargo doc --no-deps, wasm32 check — all clean	2026-09-06 19:26:51 +00:00
glm-5.3-flash	2586c3b217	feat(review 006 Unit 1): channel-open establishment phase + typed client error (E-01, N-1) Implements ADR-049 Unit 1 — the open-op wrapper gains an awaited, bounded establishment phase, and the client stops erasing the error. - OpenEstablisher hook + Establishment/EstablishmentError types: register_openable_with_establisher awaits the establisher bounded (earlier of dispatch deadline and per-registration timeout, else ESTABLISHMENT_TIMEOUT = 10s) after allocation, before the reply and before the pump handler is spawned (ADR-049 §1/§2). Implementation note: the establisher takes (input, auth) only — the channel's yield-once BiStream belongs exclusively to the pump handler (amendment recorded in ADR-049). - Establishment failure: teardown_channel + opener-ledger take + policy.on_close un-increment (allocation and teardown balance; the ledger take is the atomic gate, ADR-047 §7), reply channel:open_failed with details {reason, message} — reason ∈ dial_failed / unknown_resource / resource_shortage / handler_error / timeout (ADR-049 §3). SSH contract consumer-visible: a failed open never returns a channel_id. - register_openable unchanged (no establisher = always-OK; existing registrations compile and behave identically — compat gate test). - ChannelClient::open_channel returns ChannelOpenError (breaking at 0.5.0): CallFailed { error: CallError } carries the wire error verbatim (establishment_reason() branches on details.reason); MissingChannelId / AdoptFailed cover the local-only shapes (ADR-049 §4, review 006 N-1). - Tests cover all four verification gates from the review: e2e establisher failure through a real channels connection (typed reason + no-channel + ledger un-increment), bounded timeout, no-establisher compat, establisher-success pump round-trip; plus reason-vocabulary mapping and bound arithmetic. - Bump to 0.5.0 (open_channel error-type change is semver-relevant). Verification: cargo test (608 passed), clippy --all-targets -D warnings, fmt --check, doc --no-deps, wasm32 check — all clean.	2026-09-06 19:00:04 +00:00
glm-5.3-flash	48ceeba55c	docs: ADR-049 channel-open establishment phase; verify review 006 Verify review 006's findings against source at `88e3f5e` (E-01..E-04 all confirmed; E-02 cost corrected — OperationSpec has no description field, four touchpoints) and file three additional findings from the same sweep (N-1 client error-type gap, N-2 write-only early-arrival counter, N-3 pump-panic posture). ADR-049 resolves E-01 + N-1: split-hook OpenEstablisher awaited bounded by the open-op wrapper (restoring ADR-047 §3's "channel plan" shape), teardown + typed channel:open_failed reply on establishment failure, ChannelClient::open_channel typed error. Review 006 gains the post-verification remediation plan and verdict appendix. Verification: cargo test (597 passed), cargo doc --no-deps clean.	2026-09-06 10:57:20 +00:00
glm-5.3-flash	88e3f5e9c3	docs: review 006 — channel-open establishment gap (from alktunnels phase 0) Design review from the alktunnels Phase 0 research pass, verified against tree `a22b2b8` (0.4.1). Findings numbered E-01..E-04: - E-01 [major] — the open op cannot fail after allocation: the wrapper replies {channel_id} the moment the OpenHandler is spawned; establishment failures (params-valid-but-rejected, backend lookup failure, target dial failure) present to the consumer as a successful open followed by an instant, indistinguishable clean EOF (implicit-EOF mux path + unified poll_read EOF arms). SSH semantics (RFC 4254 §5.1 open-failure reply with reason codes; channel never exists opener-side), SOCKS5 reply codes, and udpgw's opaque ERR bit (counterexample) surveyed in alktunnels/docs/research/ssh-socks5-survey.md. alktty's in-band error-frame mechanism (send_negotiation_error, 0x00-peek) is the per-crate workaround this upstream establisher obsoletes for the channels path. Proposed shape: an awaited establishment hook (OpenEstablisher) or await-and-inspect OpenHandler, tearing down on failure and replying channel:open_failed with SSH-four reason codes in ADR-016 details. Remediation sketch + verification gates included. - E-02 [minor] — services/list discloses no per-op metadata; OQ-40 (channel/resources/subscribe) becomes load-bearing for the first time via the alktunnels discovery resolution (OQ-TN-08). - E-03 [minor] — OpenHandler-exit vs channel/close teardown race is benign (ledger take is the gate) but the let _ = discard at operations.rs:509 is silent; recommend log-or-comment. - E-04 [minor] — early-arrival park cap (64) is an observable bound for push-first producers under slow adopters; no change requested, filed so the constraint is visible to the next consumer. Non-findings recorded: open-op ACL path complete across all three dispatch entry points; input_schema enforcement covers open params; EOF arms unified; channel_open marker + resource_id_path wire round-trip intact; opener-ledger decrement atomic at every call site. alkcall tests: 597 passed (docs-only change; baseline check).	2026-09-06 09:54:13 +00:00