fix: add workaround for Claude Code classifyHandoffIfNeeded bug (#480)

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>

get-shit-done/workflows/execute-plan.md

@@ -111,6 +111,12 @@ Pattern B only (verify-only checkpoints). Skip for A/C.
    - Verify key-files.created exist on disk with `[ -f ]`
    - Check `git log --oneline --all --grep="{phase}-{plan}"` returns ≥1 commit
    - Append `## Self-Check: PASSED` or `## Self-Check: FAILED` to SUMMARY
+
+   **Known Claude Code bug (classifyHandoffIfNeeded):** If any segment agent reports "failed" with `classifyHandoffIfNeeded is not defined`, this is a Claude Code runtime bug — not a real failure. Run spot-checks; if they pass, treat as successful.
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 </step>
 
 <step name="load_prompt">