Fixes from self-review of formula parser and bd cook:
1. Atomicity: Add cleanup on failure in cookFormula - if labels/deps
transaction fails, delete the already-created issues
2. Validation: Add recursive depends_on validation for child steps
and validate priority ranges for children
3. Documentation: Mark unimplemented fields (Expand, ExpandVars,
Condition, Gate) with TODO(future) comments
4. Thread safety: Add note that Parser is NOT thread-safe
5. Error messages: Track first definition location for duplicate ID
errors (e.g., "duplicate id at steps[1], first defined at steps[0]")
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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