fix: report issue work timeout cause

[jeremymcs]

Summary

• use the agent-aware failure summarizer for failed issue work
• surface the terminal timeout instead of early Codex startup/cache warnings
• add regression coverage for the reported base_instructions cache warning followed by exit 124

Root cause

Codex continued running after the models-cache parse warning. Patchdeck later timed it out, but issue work displayed the beginning of raw stderr and hid the appended timeout reason at the end.

Verification

• node --import tsx --test --test-name-pattern='reports a Codex timeout instead of a models cache warning' server/issueWorkAgent.test.ts
• node --import tsx --test server/agentRunner.test.ts server/issueWorkAgent.test.ts
• npm run test (701 passed)
• npm run check
• node --experimental-test-coverage --import tsx --test server/agentRunner.test.ts server/issueWorkAgent.test.ts (issueWorkAgent.ts: 92.42% lines, 74.42% branches)

[github-actions]

📄 Documentation Review Reminder

This PR changes source files but does not update any public documentation.

Changed source files:

server/issueWorkAgent.test.ts
server/issueWorkAgent.ts

Please check if documentation in docs/public/ needs to be updated:

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• Documentation updated in this PR
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