fix(work): surface captured output on a headless agent timeout instead of discarding it

[getappz]

Summary

• run_headless's timeout branch (src/agent_launch.rs) discarded the child's already-captured stdout/stderr and reported only "<agent> timed out after Ns" — even though run_captured retains whatever the process wrote before being killed.
• Found live: an agentflare work <item> --agent opencode run completed all of its actual work (4 commits, pushed to a branch) and then hung on something afterward; the timeout failure comment posted to the item said only "timed out", with nothing distinguishing it from a run that made zero progress. Had to manually dig through git branches to discover real work existed.
• Fix: on timeout, include a tail (last 2000 chars, UTF-8-safe) of captured stdout (or stderr if stdout is empty) in the Failed message, so the item comment/CLI output actually shows what the agent was doing when it was killed.

Test plan

• run_captured_keeps_output_written_before_a_timeout_kill — proves output written before a kill survives in Captured, which the fix depends on
• tail_str unit tests, including a UTF-8 multi-byte boundary case
• diagnostic_suffix unit tests: empty-output case, stdout-preferred case, stderr-fallback case
• Full existing agent_launch:: suite still passes (20/20)

Summary by CodeRabbit

• Bug Fixes
  • Improved timeout failure messages with captured diagnostic output.
  • Diagnostics now prefer standard output, fall back to error output, and clearly indicate when no output is available.
  • Long diagnostics are safely limited to the final 2,000 characters without breaking multibyte text.
  • Timeout diagnostics now provide more actionable details for troubleshooting failed launches.

[coderabbitai]

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📝 Walkthrough

Walkthrough

Headless timeout failures now include captured stdout or stderr diagnostics. Output is limited to the final 2,000 UTF-8-safe characters. Tests cover capture, truncation, multibyte text, and source selection.

Changes

Headless timeout diagnostics

Layer / File(s)	Summary
Diagnostic capture and validation src/agent_launch.rs	Timed-out headless runs prefer stdout, fall back to stderr, and report when no output exists. Diagnostics use UTF-8-safe tail truncation at 2,000 characters. Tests verify capture after process termination, truncation, multibyte boundaries, and source selection.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• getappz/agentflare#155: Introduces the timeout handling extended here with captured stdout and stderr.

Suggested labels: rust

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: exposing captured output when a headless agent times out.
Description check	✅ Passed	The description includes a detailed summary and test plan, but it omits the optional Notes for reviewers section.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/work-timeout-diagnostics

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/agent_launch.rs`:
- Around line 312-325: Update diagnostic_suffix to select stdout whenever
captured.stdout is non-empty, without calling trim on either stream; otherwise
select stderr when non-empty, preserve the no-output fallback, and pass the
selected original stream directly to tail_str.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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📥 Commits

Reviewing files that changed from the base of the PR and between c20aa47 and b2e188f.

📒 Files selected for processing (1)

• src/agent_launch.rs