fix(opencode): repair chatgpt subscription hang watchdog

[liuhaoyang]

Fixes #29420

Summary

Repair the stream watchdog for ChatGPT subscription streams to properly detect and recover from hung connections.

Changes

• Provider request timeout (provider.ts): Replace broken AbortSignal.timeout() with manual setTimeout + AbortController for a 5-minute default request timeout. Properly clean up timers in finally block and re-throw abort reasons on cancellation.
• Stream watchdog (processor.ts): Add watchStream() wrapper with separate first-byte (30s) and idle (120s) timeouts using Promise.race. Wire into the LLM stream consumption path and cap retries at 3 attempts.
• Timeout error handling (message-v2.ts): Convert DOMException(TimeoutError) from watchdog into retryable APIError so the retry loop can recover.
• Retry classification (retry.ts, error.ts): Extend transient error detection to recognize 429/502/503/504 status codes, rate-limit messages, overloaded/gateway-timeout patterns, and deeply-nested ChatGPT error bodies (with depth protection against circular refs).
• Abort signal propagation (codex.ts): Thread AbortSignal through exchangeCodeForTokens(), refreshAccessToken(), and waitForOAuthCallback() so Codex auth operations respect caller cancellation.
• Subagent timeout (task.ts): Add configurable 5-minute default timeout on subagent tasks with input validation rejecting non-positive values.
• Tests: Add processor watchdog tests (first-byte stall, idle stall, early compaction cleanup), retry classification tests for transient errors, Codex signal propagation test, subagent timeout tests, and timeout constant assertion.

Test Plan

• Verify watchdog triggers on hung subscription streams (first-byte and idle timeouts)
• Verify normal streams are not affected by the watchdog
• Verify timeout recovery works correctly (retry then fail after max attempts)
• Verify provider request timeout fires after 5 minutes of no response
• Verify abort signal propagates through Codex token refresh
• Verify subagent tasks time out and cancel child session
• Verify 429/502/503/504 errors are classified as retryable

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