fix: upload failure logs to PR when agent tool fails without sessionId

[konard]

Summary

Fixes #1287 - When --tool agent fails (e.g., due to rate limit), the solve command should upload failure logs to the PR even if no sessionId was established.

Root Cause

The log upload condition in solve.mjs required sessionId to be truthy:

if (shouldAttachLogs && sessionId && global.createdPR && global.createdPR.number) {

However, when the agent fails early (e.g., rate limits before any work is done), no sessionId is assigned, causing failure logs to never be uploaded to the PR.

Changes

1. Fix log upload condition (src/solve.mjs)

• Remove sessionId requirement from the failure log upload condition
• Now aligns with the pattern in handleFailure() from solve.error-handlers.lib.mjs
• Logs will be uploaded when --attach-logs is enabled and a PR exists

2. Add FreeUsageLimitError detection (src/usage-limit.lib.mjs)

• Add freeusagelimiterror pattern to detect Agent/OpenCode Zen rate limit errors
• This enables proper usage limit detection for the agent tool

3. Improve rate limit detection (src/agent.lib.mjs)

• Check multiple sources for usage limit detection:
  1. lastMessage (the last chunk of output)
  2. errorMatch (the extracted error message from JSON output)
  3. fullOutput (complete output - fallback)
• This ensures rate limits are detected regardless of where they appear in the output

4. Add case study documentation (docs/case-studies/issue-1287/)

• Detailed timeline of events from the original failure
• Root cause analysis
• Error details in JSON format
• Full log file from the issue

5. Add tests (tests/test-usage-limit.mjs)

• Test for FreeUsageLimitError detection
• Test for agent rate limit error message detection

Test Plan

• All existing tests pass (65/65)
• ESLint passes
• New tests for FreeUsageLimitError detection pass
• Manual test with --tool agent --attach-logs on a rate-limited scenario

Evidence

From the original log file, the agent returned:

{
  "type": "error",
  "exitCode": 0,
  "errorDetectedInOutput": true,
  "errorType": "AgentError",
  "errorMatch": "Failed after 3 attempts. Last error: Rate limit exceeded. Please try again later.",
  "sessionId": null,
  "limitReached": false,
  "limitResetTime": null
}

The sessionId: null caused the log upload to be skipped even though --attach-logs was enabled.

---

🤖 Generated with Claude Code

[konard]

🤖 Solution Draft Log

This log file contains the complete execution trace of the AI solution draft process.

💰 Cost estimation:

• Public pricing estimate: $5.784912
• Calculated by Anthropic: $3.899087 USD
• Difference: $-1.885825 (-32.60%)
  📎 Log file uploaded as Gist (1031KB)
  🔗 View complete solution draft log

---

Now working session is ended, feel free to review and add any feedback on the solution draft.