Claude Code v2.1.27+ has a bug where all Task tool agents report
"failed" due to `classifyHandoffIfNeeded is not defined` — a function
called but never defined in the cli.js bundle. The error fires AFTER
all agent work completes, so actual work is always done.
This adds spot-check fallback logic to execute-phase, execute-plan,
and quick workflows: when an agent reports this specific failure,
verify artifacts on disk (SUMMARY.md exists, git commits present).
If spot-checks pass, treat as successful.
Tracked upstream: anthropics/claude-code#24181
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
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