**Goal**: Prevent response.failed events with `invalid_prompt` from
being treated as retryable errors so the UI shows the actual error
message instead of continually retrying.
**Before**: Codex would continue to retry despite the prompt being
marked as disallowed
**After**: Codex will stop retrying once prompt is marked disallowed
- capture the header from SSE/WS handshakes, store it per
ModelClientSession using `Oncelock`, echo it on turn-scoped requests,
and add SSE+WS integration tests for within-turn persistence +
cross-turn reset.
- keep `x-codex-turn-state` sticky within a user turn to maintain
routing continuity for retries/tool follow-ups.
Context
- This code parses Server-Sent Events (SSE) from the legacy Chat
Completions streaming API (wire_api = "chat").
- The upstream protocol terminates a stream with a final sentinel event:
data: [DONE].
- Some of our test stubs/helpers historically end the stream with data:
DONE (no brackets).
How this was found
- GitHub Actions on Windows failed in codex-app-server integration tests
with wiremock verification errors (expected multiple POSTs, got 1).
Diagnosis
- The job logs included: codex_api::sse::chat: Failed to parse
ChatCompletions SSE event ... data: DONE.
- eventsource_stream surfaces the sentinel as a normal SSE event; it
does not automatically close the stream.
- The parser previously attempted to JSON-decode every data: payload.
The sentinel is not JSON, so we logged and skipped it, then continued
polling.
- On servers that keep the HTTP connection open after emitting the
sentinel (notably wiremock on Windows), skipping the sentinel meant we
never emitted ResponseEvent::Completed.
- Higher layers wait for completion before progressing (emitting
approval requests and issuing follow-up model calls), so the test never
reached the subsequent requests and wiremock panicked when its
expected-call count was not met.
Fix
- Treat both data: [DONE] and data: DONE as explicit end-of-stream
sentinels.
- When a sentinel is seen, flush any pending assistant/reasoning items
and emit ResponseEvent::Completed once.
Tests
- Add a regression unit test asserting we complete on the sentinel even
if the underlying connection is not closed.
