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alkcall/docs/architecture/open-questions.md
glm-5.2 f305f8c0a5 feat: implement channels protocol + ADR-047 (openable ALPNs are operations) 
ADR-047: the unifying decision that  dissolves into
per-ALPN ops (, ) with a
 marker on . Each openable ALPN registers
its own ops with their own , ,
, and the marker. The  field is replaced
by  (Sub/Pub). The generic ops (channel/close,
channel/control, channel/resources/subscribe) stay, keyed by
channel_id. Resolves Gaps A-G from the research findings (Gap B broker
named out-of-scope for alkcall; Gap C relay wrapper is consumer
concern; Gap D connection-owner allocates; Gap E extension trait;
Gap F boolean marker on wire; Gap G ACL/ownership complementary).

ADR-037 amended:  dissolves;  removed; generic
ops stay;  preview dropped from resources/subscribe.

Spec docs updated: channel-operations.md (unified model, opener ledger,
ACL flow), operation-registry.md (channel_open marker, ChannelOpenSpec),
README.md (ADR-047), open-questions.md (OQ-31..38 resolved).

Source changes:
- spec.rs: ChannelOpenSpec struct, channel_open field on OperationSpec,
  with_channel_open builder, 3 tests
- discovery.rs: spec_to_json emits channel_open boolean,
  operation_spec_schema includes channel_open, 2 tests
- from_call.rs: rebuild_spec_for parses channel_open marker,
  derive_alpn_from_op_name helper, 6 tests

Channels module (src/channels/, 10 files, ~2400 lines):
- wire.rs: 8-byte chunk header (ChunkHeader, parse/write_header,
  read_header/write_chunk/write_eof async helpers), 12 tests
- reassembly.rs: MpscRecvStream (tokio::mpsc::Receiver<Bytes> →
  AsyncRead), MpscSendStream (AsyncWrite → tokio::mpsc::Sender<Bytes>),
  REQ-CH-01 shutdown sentinel, REQ-CH-02 sender-drop EOF, 10 tests
- mux.rs: MuxHandle (clone-able, register(channel_id)),
  MuxRunner (per-channel pump tasks, exits when handles drop),
  OpenerLedger (ADR-047 §7), 4 tests
- manager.rs: ChannelManager (channel map, open_channel,
  install_channel_zero, route_payload, teardown_channel, clear_all),
  11 tests
- source.rs: ChannelBidiStreamSource (yield-once accept_bi),
  channel_source helper, 4 tests
- adapter.rs: ChannelsAdapter (ProtocolHandler for alknet/channels,
  demux loop, install_channel_zero hook), 1 test
- operations.rs: ChannelOperations (registers channel/close,
  channel/control, channel/resources/subscribe), ChannelCore
  (check_open/on_close wrappers), 4 tests
- policy.rs: ChannelLifecyclePolicy trait, NoCap, PerIdentityChannelPolicy
  (default 256, per_identity_caps override), default_policy, 8 tests
- env.rs: ChannelOperationEnv extension trait (ADR-047 §4),
  ChannelsSessionEnv impl, 2 tests
- client.rs: ChannelClient (from_connection, call_open_op,
  take_call_connection), 1 test

Verification: 432 tests pass (66 new channels + 10 marker + 356
existing), clippy clean, fmt clean, cargo doc generates.

Cargo.toml: +bytes dependency.
2026-08-12 12:13:53 +00:00

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7.3 KiB
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---
status: draft
last_updated: 2026-08-12
---
# Open Questions
Open questions are tracked here, organized by theme. Each question has a
status, priority, and (when resolved) a resolution citing the ADR.
**Status values**: `open`, `resolved`, `deferred(scope)`, `deferred(unclear)`,
`partially resolved`, `dissolved`.
## Call Protocol
| OQ | Title | Status | Priority | Resolution |
|----|-------|--------|----------|------------|
| OQ-01 | Call protocol scope within a connection | resolved | medium | ADR-015 — stream model, multiplexing |
| OQ-02 | Operation path format and routing scope | resolved | medium | `/{service}/{op}` is the correct design |
| OQ-03 | Batch operation semantics | resolved | low | Correlated call.requested events |
| OQ-04 | Session-scoped operation registries | resolved | medium | ADR-019 — OperationEnv trait layering |
| OQ-05 | Abort cascade semantics for nested calls | resolved | high | ADR-020 |
| OQ-06 | Privilege model and authority context | resolved | high | ADR-017 |
| OQ-07 | Handler identity registration path and composition authority | resolved | high | ADR-018 |
| OQ-08 | Operation error schemas | resolved | high | ADR-016 |
| OQ-09 | Safe vault operations for call protocol exposure | resolved | high | ADR-010 — none exposed |
| OQ-10 | ~~Remote-safe marking shape~~ | dissolved | medium | ADR-024 — remote_safe/trusted_peer retired |
| OQ-11 | OperationAdapter error type (AdapterError variants) | resolved | medium | DiscoveryFailed, SchemaParse, Transport, Unauthorized, SamePeerCollision |
| OQ-12 | from_call re-import trigger | resolved | low | ADR-028 — manual free function |
| OQ-13 | from_call namespace collision | resolved | low | Same-peer = error; cross-peer dissolved (ADR-024) |
| OQ-14 | CallClient TLS client-auth | resolved | high | quinn client-auth; key-type-aware verification |
| OQ-15 | PeerRef::Any routing policy | resolved | low | Insertion-order first-match |
| OQ-16 | services/list-peers re-export semantics | resolved | low | Opt-in; services/list is own-ops-only |
| OQ-17 | Multi-hop federation | deferred(scope) | low | One-hop model is the commitment; multi-hop is a feature extension |
| OQ-18 | PeerId — crypto identity vs stable logical id | resolved | high | ADR-025 — PeerId = Identity.id (stable) |
| OQ-19 | Persistent peer registry | resolved | medium | ADR-025 — core trait + in-memory default; persistence adapters separate |
| OQ-20 | ~~API key asymmetry~~ | dissolved | medium | PeerEntry supports multiple credential paths |
| OQ-21 | X.509 outgoing-only case | resolved | medium | Three remote roles; PeerEntry asymmetry correct |
## Call Protocol — Pub/Sub
| OQ | Title | Status | Priority | Resolution |
|----|-------|--------|----------|------------|
| OQ-22 | Call protocol pub/sub primitive — pub to go with sub | partially resolved | high | ADR-046 resolves the primitive: `OperationType::Pub` + `HandlerKind::Sink` + `call.published` wire event + `invoke_sink()` dispatch path. The fan-out/broker mechanism (one producer, N consumers, topic matching) is deferred to the channels session — the call protocol is point-to-point; the broker is a routing concern that sits above it. ADR-047 §1 names the broker (Gap B) as out-of-scope for alkcall; the hub composes it on top of the `Pub`/`Sub` primitives. See §"Pub/Sub Gap" below. |
### Pub/Sub Gap
The call protocol's `StreamingHandler` / `invoke_streaming()` path
(ADR-021) is point-to-point: a `call.requested` arrives, the handler
produces a stream of `call.responded` events back to that one caller.
There was no mechanism for a producer to stream data *to* a responder
(client→server streaming), and no fan-out (one producer, N consumers).
**ADR-046** resolves the directional gap: `OperationType::Pub` is the
client→server streaming complement to `Sub` (was `Subscription`,
renamed for symmetry). `HandlerKind::Sink` is the consuming handler
type. `call.published` is the wire event carrying stream chunks.
`invoke_sink()` is the dispatch path. `CallConnection::publish()` is
the client method. The `Subscription` variant is renamed to `Sub`
(wire string `"sub"`).
**Fan-out deferred.** The broker (topic registry, `Pub`↔`Sub` matching,
N-consumer fan-out) is deferred to the channels session. The call
protocol is point-to-point (one initiator, one responder, a stream
between them); a topic registry that outlives individual calls is a
different lifecycle and a different concern. The broker's first
consumer is the channels `channel/resources/subscribe` operation
(ADR-037) and the hub-as-broker pattern (ADR-042). The `Pub` primitive
is the load-bearing piece the broker composes on.
## Channels
| OQ | Title | Status | Priority | Resolution |
|----|-------|--------|----------|------------|
| OQ-23 | Full channel-level flow-control windowing | deferred(scope) | low | Bounded-buffer decided (ADR-040); full windowing blocked on HOL-blocking deployment observation |
| OQ-24 | Channels add/strip API shape | open | low | Whether the 8-byte header add/strip is built into the read/write path or a standalone utility. The contract (ADR-035) is decided; the function surface is not |
| OQ-31 | `channel/open` ACL granularity | resolved | high | ADR-047 — `channel/open` dissolves into per-ALPN ops; each op has its own `access_control` |
| OQ-32 | Quota lifecycle (opener vs closer, transport drop) | resolved | high | ADR-047 §7 — the per-connection opener ledger; decrement on every teardown path, keyed by opener |
| OQ-33 | Per-identity connection cap (endpoint layer) | deferred(scope) | low | Named as a separate layer (ADR-047 §"ALPN category reframe" references the findings); belongs at `alknet-endpoint`, not channels. Named to stop the re-tangle |
| OQ-34 | `channel_open` marker wire format | resolved | medium | ADR-047 §2 — boolean `"channel_open": true` in `services/schema`; ALPN derivable from op name |
| OQ-35 | `OperationEnv::channel_manager()` coupling | resolved | high | ADR-047 §4 — extension trait `ChannelOperationEnv` in `channels-call`; call crate stays free of channels types |
| OQ-36 | `channel_id` allocation in Pub case | resolved | medium | ADR-047 §5 — "connection owner allocates" (the side that holds the `ChannelManager`); amends "responder allocates" |
| 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 `alknet/` prefix; ALPNs without that prefix use the full ALPN string (rare, two-way-door) |
## Core Types
| OQ | Title | Status | Priority | Resolution |
|----|-------|--------|----------|------------|
| OQ-25 | BiStream type definition | resolved | high | ADR-005 — trait, Connection parameter |
| OQ-26 | AuthContext resolution timing | resolved | high | ADR-003 — hybrid resolution |
| OQ-27 | ALPN string naming convention | resolved | medium | ADR-004 — alknet/ prefix |
| OQ-28 | Dynamic handler registration | resolved | low | ADR-019 — curated static, overlays dynamic |
| OQ-29 | Handler-level auth resolution observability | resolved | medium | set_identity() on Connection for observability |
| OQ-30 | Dynamic resource ownership | resolved | high | ADR-011 — OwnershipProvider, resource_id_path |
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