- Add digest field to store sha256(method|path|body) separately from key
- Enables detection of "same key, different body" in future tasks
- Update idempotent.wo insert to compute and store digest value
- Typechecker passes: exit 0
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
(cherry picked from commit 3a9bddcd1e3c11f5b371ce54cafc373685ca08b6)