Stop Codex inference reads at SSE completion

[bb-slop-cop]

🚨 SLOP COP 🚨 · new-issue-autopilot

Human comments

What was wrong

The Codex inference SSE reader stored completed output but continued reading until transport EOF. It ignored [DONE] as well, so a successfully completed response with an open body became a deadline failure. This source defect is reproduced twice on trusted origin/main; attribution of the original live naming timeout remains unverified.

Report: https://get-bb.github.io/reports/issues/4828.html

What changed

• Stop reading after response.completed, response.done, or [DONE] and best-effort cancel the remaining body.
• Preserve terminal provider-error handling, final-output preference, delta fallback, and empty-output validation.
• Add six focused lifecycle regression cases in the existing real-client test harness.
• Change only two existing Codex-provider files: 91 additions + 11 deletions = 102 changed text lines. No dependencies, generated files, stored data, schemas, public wire fields, or user-facing configuration change.

How you verified

• Before the fix: pnpm exec turbo run test --filter=bb-plugin-provider-codex -- src/ai/chatgpt-client.test.ts fails in six regression cases with codex_request_timeout; 17 existing cases pass. A second clean checkout at 76a1ebcaf5fa038d8638daaad7aad3dafe2ae709 repeats the same failures.
• After the fix: the same focused command passes all 23 cases.
• pnpm exec turbo run test typecheck lint --filter=bb-plugin-provider-codex passes: 341 tests across 32 files, typecheck, and lint.
• Both clean checkouts complete frozen installs and full Turbo builds.
• pnpm exec oxfmt --check plugins/provider-codex/src/ai/chatgpt-client.ts plugins/provider-codex/src/ai/chatgpt-client.test.ts passes.
• git diff --check passes; git diff --numstat origin/main confirms 102 changed text lines and no binary changes.

Fixes #4828

AGENT GENERATED