fix(responses): finalize WebSocket stage telemetry in place

[luvs01]

Motivation

• The Codex WebSocket exchange stored a detached CodexWsStageRecord snapshot when the response committed, so logs adopted that initial object and later stream settlements could replace the WeakMap entry without updating the already-adopted attempt, producing stale telemetry ([Bug]: Long Codex thread fails only through OpenCodex proxy (WS 1006 / response prelude timeout); bypass works immediately lidge-jun/opencodex#4191).

Description

• Change markCodexWsStage to update an existing record in-place (via Object.assign) when one is already mapped to the Response, preserving the reference held by logging paths instead of replacing it; this is implemented in src/server/responses/codex-ws-wire.ts.
• Add a regression test that verifies later markCodexWsStage calls finalize the object already adopted by the logger (tests/responses/ws-failure-stage.test.ts).
• Update the transport documentation to describe the invariant that stream settlements finalize the same stage object in place (structure/transports/responses.md).

Testing

• Ran the focused WebSocket regression tests with Bun v1.4.2: mise x bun@1.4.2 -- bun test tests/responses/ws-failure-stage.test.ts, which passed all tests (15 passed, 0 failed).
• Ran repository validation steps: mise x bun@1.4.2 -- bun run structure:check, mise x bun@1.4.2 -- bun run privacy:scan, and mise x bun@1.4.2 -- bun run typecheck, all of which succeeded.
• A full bun run test was started but interrupted by unrelated existing catalog-route test expectations (not caused by these changes); the focused regression and validation checks above are green.

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Codex Task

[coderabbitai]

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[github-actions]

✅ Deterministic PR hygiene checks passed.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-14T06:39:00.252563Z	169f178	PR opened

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[luvs01]

The telemetry correction and behavioral regression coverage have been carried into the current integration submission, with validation limitations documented there. Closing this personal tracking PR to avoid duplicate implementation and follow-up work.