docs: implementation plan (TTY precedents folded in); task decomposition (17 tasks)

Plan updated with the alknet-tty findings: the drainer pattern
(single ordered writer) makes outbound chunk-boundary parsing sound;
TestStdinSink's try_send→Full→Pending is the inbound backpressure
precedent; OQ-01(a) now cites the reference.

Task graph (taskgraph-validated, 17 tasks, 6 generations, no cycles):
- tasks/server/: core-types, auth, healthz-decoy, adapter
- tasks/gateway/: dispatch, routes, publish
- tasks/websocket/: byte-adapter (research POC), upgrade-session, overlay-ops
- tasks/adapters/: from-openapi, from-jsonschema, to-openapi, from-wss, mcp
- tasks/client/: http-host
- tasks/infra/: integration-suite (phase 4)

Critical path runs through server core → adapter → WS session →
overlay tests → integration suite. High-risk tasks are the three WS
tasks, de-risked by the ws-byte-adapter POC blocking upgrade-session.

tasks/websocket/byte-adapter.md

@@ -0,0 +1,54 @@
+---
+id: ws-byte-adapter
+name: WS ↔ byte-stream adapter (research POC → production shape)
+status: pending
+depends_on: []
+scope: moderate
+risk: high
+impact: phase
+level: research
+tags: [websocket, phase-2, poc]
+---
+
+## Description
+
+Targeted POC validating the WS↔byte-stream adapter contract (OQ-01)
+before the production implementation: wrap axum's `WebSocket` as
+`AsyncRead + AsyncWrite` such that alkcall's `ChannelsAdapter` demux
+and mux run over it correctly.
+
+Inbound: axum WS messages → shared bounded buffer → `AsyncRead` drains
+(backpressure via the alknet-tty precedent: try_send → Full → Pending).
+Outbound: `AsyncWrite` accumulates into a pending buffer; a task parses
+outgoing 8-byte chunk headers (verified: header+payload are separate
+writes; channel 0's write_frame is prefix+body separately) and emits
+each complete chunk as one WS binary message; chunks over the WS
+message cap (~1 MiB default) split across messages. Close: WS close →
+transport EOF (REQ-CH-02); `AsyncWrite::shutdown` → zero-length
+sentinel then Close frame (REQ-CH-01).
+
+## Acceptance Criteria
+
+- [ ] POC: adapter + ChannelsAdapter + channel-0 Dispatcher over `tokio::io::DuplexStream` pairs — call round-trip works
+- [ ] POC test: 16 MiB chunk splits across WS messages and reassembles
+- [ ] POC test: interleaved channel writes preserve chunk integrity (no torn chunks)
+- [ ] OQ-01 sub-items (a)-(d) resolved with concrete values, written back into open-questions.md
+- [ ] Findings + go/pivot recommendation recorded in this task's Summary
+
+## References
+
+- docs/architecture/websocket.md (§The WS ↔ byte-stream adapter)
+- docs/plans/implementation.md (§What the spike established, point 6)
+- alknet-tty precedent: `src/adapter.rs` `pump_session` drainer pattern + `TestStdinSink` backpressure
+- alkcall: `channels::wire::write_chunk`, `channels::mux::MuxRunner`, REQ-CH-01/02 in `channels-wire.md`
+
+## Notes
+
+> Agent fills during implementation. This is a research task: the POC
+> code lands under `.worktrees/research/` or a `#[cfg(test)]` module —
+> not as final production code — but the production adapter may grow
+> directly from it if the shape holds.
+
+## Summary
+
+> Agent fills on completion.