v0.4.2 — Enrichment screens values instead of voiding the checkpoint

Patch release for checkpoint enrichment, fixing #2.

Fixed

• Checkpoint enrichment no longer fails on its own subject matter. The enrichment job now screens model output value by value: a transcript-, diff-, or dialogue-shaped value, an evidence item whose claim is not a verbatim part of a digest fragment, or a slug the digest never references is dropped on its own and recorded on the checkpoint as enrichment <field>: N items dropped (<reason>), which the renderer's Warnings: line shows. A credential in the output or a malformed shape still fails the job into last_error, and the store's own gate (validate_enrichment) stays all-or-nothing.
• Word guard exempts paths and identifiers. transcript, diff, and body count only as prose; transcript.py, hooks/transcript, or transcript_delta are facts a checkpoint may state.

625 tests pass. See CHANGELOG.md for the full 0.4.x history.