---
id: review-001-ws-eof-signal
name: Lossless EOF signal + pending-map sweep for from_wss (WS-02, CON-02)
status: completed
depends_on: []
scope: narrow
risk: high
impact: component
level: implementation
tags: [websocket, adapters, review-001, from-wss]
---

## Description

Review 001 findings WS-02 + CON-02 — one mechanism, verified end-to-end:

`src/websocket/byte_adapter.rs:138-139` (and the tungstenite twin at
`:319`) fires `read_eof.notify_waiters()`, which wakes only
*already-registered* waiters and stores no permit. `from_wss` spawns its
drop-monitor *after* session setup (`from_wss.rs:156-166`); if the read
task hits EOF before the monitor first polls `Notified`, the signal is
lost. `import()` does `std::mem::forget(session)` (`:193`), so the
`close_rx` fallback never fires either — the monitor never runs
`fail_all`, and in-flight imported-op calls hang (Once-calls recover only
at the 30 s sweeper *if* a sweeper runs; CON-02 establishes it doesn't on
this path — `Dispatcher::run_loop`'s sweeper is never taken; `Sub`/`Pub`
pendings hang forever). The module doc at `from_wss.rs:111-113` promises
the opposite of the behavior.

Fix both halves:

- Replace `notify_waiters` with a permit-storing signal: `tokio::sync::watch`,
  `CancellationToken`, or a checked `AtomicBool` — anything a late
  subscriber observes. Apply to both the axum and tungstenite pump paths.
- Extend the from_wss monitor to sweep the pending map periodically while
  the session lives (or otherwise ensure post-`fail_all` registrations
  still resolve), since calls registered after the one-shot `fail_all`
  are currently never resolved.

Acceptance gates from the review: (1) a from_wss test that drops the
connection **while a call is being registered** — the CON-02 race — with
no hang; (2) the module doc's promise ("no hang") becomes true.

## Acceptance Criteria

- [x] EOF-notify is stored (late subscriber observes it) — race test: drop during session setup/first call registration resolves all in-flight calls as retryable
- [x] Post-`fail_all`-registered pendings also resolve (sweep or equivalent), not hang forever
- [x] The `connection_drop_fails_in_flight_calls_retryable_no_hang` test remains green; add the racing-drop variant (COV gap 10)
- [x] Module doc at `from_wss.rs:111-113` matches implemented behavior
- [x] `cargo test` and `cargo clippy --all-targets -- -D warnings` pass

## References

- docs/reviews/001-initial-implementation-review.md (Part B, WS-02; Part G, CON-02; COV-03)
- docs/architecture/decisions/070-from-wss-consumer-adapter.md

## Notes

> Agent fills during implementation. Highest-priority WS fix — lossy
> notification hangs calls; everything else in the WS subsystem can
> follow.

## Summary

Replaced the `Notify`-based read-EOF signal in `WsPumps` (both axum and
tungstenite pump paths in `byte_adapter.rs`) with a retained
`tokio::sync::watch` channel (`Sender<bool>`/`subscribe()` receiver) —
the lossless EOF property WS-02 required. The `from_wss` drop monitor
now selects on `eof_rx.changed()` / `close_rx` / a 1 s sweep tick: on
EOF it fails all pendings with retryable `CONNECTION_CLOSED` and keeps
sweeping every tick so calls registered *after* the initial `fail_all`
(the `std::mem::forget` fire-and-forget import path) are also failed —
the CON-02 no-hang guarantee, independent of registration-vs-EOF
ordering. `std::mem::forget` semantics were left untouched per the task
scope.

Tests (in `from_wss.rs` `mod tests`): a killable producer harness
(`drop_on_signal_producer` — the upgrade handler stashes the server
side's `WsPumps` in a slot the test can `abort()`, forcing consumer-side
EOF deterministically); `forget_session_drop_during_call_registration…`
and `held_session_drop_during_call_registration…` cover the CON-02 race
(EOF before/during registration → call resolves Err, no hang); the
`call_registered_after_eof…` test registers a call well after EOF and
asserts the sweep resolves it retryable; the original
`connection_drop_fails_in_flight_calls_retryable_no_hang` stays green.
One tolerated outcome note: the held-session race can also resolve via
alkcall's write-failure path (`failed to write request frame`,
`INTERNAL` — the mux dies between registration and write), which is
prompt-but-not-retryable; that path is accepted in the race tests (the
retryable assertion lives with the sweep and pre-drop tests where the
call is guaranteed in-flight).

Verification: cargo test 219 ok; cargo test --features wss 231 ok (3x
flake check); cargo clippy --all-targets -- -D warnings (default;
all-features blocked only by an unrelated in-flight
`src/server/adapter.rs` edit from a parallel agent);
cargo fmt --check.