fix(ai): harden Codex streaming transport

[fettpl]

Summary

• decode Codex SSE streams line-by-line across LF, CRLF, mixed/CR framing, split line endings, split UTF-8, comments, multiline data, and terminal EOF events
• reject pre-aborted WebSocket requests before construction, cache acquisition/reuse, send, or parse, and normalize cancellation through a shared AbortError path
• clean listeners/sockets on connection failure, stream cancellation, cached-socket abort, fallback close/error, and every terminal settlement

Verification

• focused issue regression: 15/15 passed
• combined new and existing Codex stream suites: 32/32 passed
• npm run check

Compatibility

• no public API, model catalog, or daemon protocol change
• cached sockets remain reusable after successful requests; active aborted sockets are evicted

Fixes #941

Note

Fix Codex SSE framing and WebSocket cancellation in streaming transport

• Adds CodexSSEDecoder to handle mixed/split line endings (LF, CRLF, CR) and dispatch terminal SSE events without a trailing blank line, fixing dropped final events.
• Hardens WebSocket lifecycle: pre-aborted requests, mid-setup aborts, and abort-during-streaming now all close sockets with a clear reason and propagate a consistent AbortError.
• Centralizes abort detection with throwIfAborted, isAbortError, and createAbortError helpers; sleep now cleans up its abort listener to prevent leaks.
• Adds Vitest tests covering SSE framing edge cases and WebSocket cancellation scenarios including cached socket eviction and SSE fallback.
• Behavioral Change: aborted requests now set stopReason to 'aborted' with error message 'Request was aborted' instead of silently masking the abort.

^{Macroscope summarized 6eb7f43.}

[fettpl]

@snimu This is ready for review. It hardens Codex SSE framing across split/mixed line endings and terminal EOF events, and makes WebSocket pre-abort, cache, send, fallback, and cleanup behavior deterministic.

Independent review is clean. All required CI checks pass at 6eb7f43b35866b5f455a817872b85b271efa8544.

[sethkarten]

Thank you for the report and proposed work. This root cause is now covered by maintainer-owned stacked PR #1164, authored independently from upstream/main.

We did not inspect or reuse this PR's diff, branch, commits, implementation code, or tests; its public description/comments were used only as a bug report. To keep one review surface, this PR is superseded by #1164 and is being closed.

The complete review stack is #1158–#1165. It is being left unmerged for human review after CI and review-bot findings are cleared.