v0.19.42

Custom-floor ^file$ write-gate correctness fix (client-side; no server change).

• FIX (silent coverage gap): a custom floor whose paths used an exact-file anchor like ^tier_config.py$ matched the CLI preview and the commit gate but silently missed the WRITE gate — the write gate classified against the absolute file path while preview and commit gate use repo-relative paths. build_change_diff now canonicalizes the classifier path to repo-relative at the emission choke point (identity only; filesystem reads keep the raw path), so ^file$ floors fire at the write gate exactly as at the commit gate.
• floors check now flags a bare ^filename$ anchor with the (^|/) rewrite (loud, non-failing) so a fragile path form is never silently blessed; the define-custom-floors skill teaches the (^|/) form.

Designed via deliberate_coding (unanimous) and audited via audit_coding on each commit; verified with a negative-tested regression guard and an independent adversarial review. The 0.19.39 server prefix rule remains live; no redeploy.