[thorwhalen]

Closes #670

What. an/stores/transcripts.py delegates artifact: references to lacing (reeleehq/lacing#95, released in lacing 0.0.65, already a core dependency, imported lazily as before).

• Parsing and formatting: ArtifactRef.parse(...).locate(mall, default_store=...) and ArtifactRef.format().
• Resolution: resolve_in_mall, which tries the key first, scans only when the key no longer holds the pin, and checks the bytes against the pin.
• Removed outright, not wrapped: parse_artifact_ref, ARTIFACT_REF_PREFIX, _REF, _PINNED, _pinned, _holds, _record, _has. Nothing else in the fleet imports them.
• is_artifact_ref still accepts Artifact objects.
• TranscriptLinkError messages stay distinct: no such store, no such key, content no longer kept, not an artifact store, damaged record, and a new "does not match its pin".

Behaviour changes accepted (from lacing):

• A pin in capitals is read as a pin, lowercased.
• Text without artifact: is refused by name instead of having its prefix sliced off.
• artifact:takes/ looks up key takes/ in the transcripts store.
• record_transcript refuses keys that no reference could name (with whitespace, or starting with /).

Compatibility kept: pin_of still reads a reference an older an recorded under a key lacing now refuses, such as transcripts/my take@<sha>. Without that, an cache gc would collect the transcript a take names. A refused key read back is formatted as it was recorded instead of raising a bare ValueError.

Tests: recorded-voices, import-firewall and gc tests plus doctests: 132 passed, 4 skipped (the cut-out genre is not installed here). The new test covers lacing reading the reference, the distinct refusals, a pin in capitals, refused keys, and an older an's key.

Implementation: an Opus worker subagent, reviewed by a separate fresh Opus subagent.

Adversarial review: ship with fixes.

• Fixed: pin_of lost older references with spaces in the key, which could have let gc delete a take's transcript.
• Fixed: an Artifact held under such a key raised a bare ValueError.
• Accepted: an Artifact whose record exists but whose bytes are gone is now told "no record holds it" (main said "its content is missing").
• Not done: the pin-mismatch message has no test; the reviewer checked it by hand.

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