Pins the contract that repo/branch identity in the synced skill-usage.jsonl is
stripped before the remote POST. Three checks: a floor (the three known fields),
coverage (every repo/branch field a producer writes into skill-usage.jsonl is
stripped, so a future producer rename can't silently leak), and behavior (runs
the actual sed strip expressions over a sample event). Scoped to the synced
file, so the local-only timeline branch field is correctly excluded.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>