docs: ws-byte-adapter POC complete (GO) — resolve OQ-01, update framing facts

POC at /workspace/ws-byte-adapter-poc/ (not on main), all tests green:
- call round-trip over axum WS ↔ adapter ↔ ChannelsAdapter ↔ channel-0
  Dispatcher (published alkcall API only, no forks)
- 3 MiB payload splits across 1 MiB WS messages, byte-intact reassembly
- 20 interleaved calls reassemble without corruption/cross-correlation

Findings merged:
- OQ-01 resolved: byte-stream both directions, bounded mpsc (64 slots)
  inbound, outbound chunk-header parsing (frame-as-two-chunks
  live-confirmed), 1 MiB message cap with split, flush no-op, close →
  EOF → REQ-CH-02
- websocket.md: chunk ≠ frame on channel 0 (frame reassembly required);
  operationId is the request payload key
- task ws-byte-adapter → completed with full Summary; ws-upgrade-session
  unblocks

docs/architecture/open-questions.md

@@ -14,32 +14,28 @@ with their resolutions; new alkhttp OQs start at OQ-01.
 ### OQ-01: WS ↔ byte-stream adaptation semantics
 
 - **Origin**: [websocket.md](websocket.md), [ADR-067](decisions/067-websocket-carries-channels.md)
-- **Status**: open
+- **Status**: resolved (POC `ws-byte-adapter`; validated end-to-end — see
+  the task's Summary in `tasks/websocket/byte-adapter.md`)
 - **Priority**: high
-- **Question**: The channels demux consumes bytes (`read_exact` on the
-  8-byte header + payload); the mux writes chunks as contiguous byte
-  sequences. A WebSocket is message-oriented. The adapter's contract
-  needs nailing down before implementation:
-  (a) inbound buffer bound (the alknet-tty precedent — bounded mpsc
-  with `try_send` → `Full` → `Pending` backpressure, and the single-
-  drainer ordered-write pattern from `pump_session` — is the working
-  reference; bound value to lock during implementation);
-  (b) write-side chunk boundary parsing (verified against alkcall
-  source: the mux emits one mpsc payload per chunk, but a logical
-  write above the mux — e.g. channel 0's `write_frame`, which issues
-  prefix and body as separate `write_all`s — can surface as multiple
-  chunks; the adapter must parse outgoing chunk headers rather than
-  assume write-per-chunk; also confirm the WS-message cap policy for
-  chunks up to `MAX_CHUNK_LEN` = 16 MiB — split across messages, and
-  what the practical cap is for browser stacks);
-  (c) flush mapping (`AsyncWrite::flush` → WS message emission point);
-  (d) close mapping (WS close code → transport EOF → REQ-CH-02
-  teardown; `AsyncWrite::shutdown` maps to the zero-length EOF
-  sentinel (REQ-CH-01) then a WS Close frame — confirm this ordering
-  against the mux's pump-exit behavior).
-- **Blocked on**: nothing (the spike resolved the factual
-  sub-questions; the remaining items are implementation decisions to
-  lock during the WS adapter task)
+- **Resolution**: The adapter treats the WS message stream as a byte
+  stream in both directions; the 8-byte chunk header is the only
+  framing. Inbound: WS read task → bounded mpsc (64 slots; backpressure
+  = send awaiting capacity, applying TCP-level backpressure to the
+  socket) → `AsyncRead` drains; channel close = EOF. Outbound: a writer
+  task parses 8-byte chunk headers out of the pending byte buffer (live-
+  confirmed: a single response frame arrives as TWO chunks —
+  `write_frame`'s prefix and body surface as separate mux payloads) and
+  emits one WS message per chunk, splitting at a 1 MiB
+  `WS_MESSAGE_CAP` (receiver's boundary is the chunk header, not the
+  message). Flush is a no-op (writes queue; the writer task emits
+  independently). Close: WS close → read EOF → REQ-CH-02 teardown;
+  `shutdown` closes the write channel (mux pumps emit zero-length
+  sentinels on sender drop). Client-side consequence: chunk ≠ frame —
+  channel-0 consumers reassemble length-prefixed frames from the byte
+  stream; and the dispatcher reads `operationId` from the request
+  payload.
+- **Cross-references**: ADR-067, [websocket.md](websocket.md),
+  tasks/websocket/byte-adapter.md
 
 ### OQ-02: `/publish` body framing details