[plainprogrammer]

Closes #176

What changes

The Art index panel on /admin/catalog and the art line of catalog:status[mtg] no longer say a plain "Ready." for a finished build that doesn't match what the instance runs now (spec 053, docs/specs/053-art-index-drift/).

First question (ruled), answered from the code and a request example:

Drift	What the scanner does	Shown now
Settings (settings_digest ≠ current)	Refuses it: the page is offered the newest file whatever its digest and the route serves it (200), but parseIndex throws on the header digest and the page reads "Artwork matching isn't available. The scanner is reading text only."	A state of its own: "Out of date. Built with other settings, so the scanner can't use it. Build the art index again." with "Built with settings" and "Current settings" facts, button enabled; catalog:status reads "Art matching: out of date (…)"
Catalog (catalog_version ≠ the latest applied refresh's source_version)	Keeps using it: the header holds no catalog version, nothing checks it; newer artworks just get no art evidence	"Ready." plus a last "Warning" fact naming both versions; catalog:status appends " Warning: built from catalog …"

Judged only for a finished latest build whose file is on disk (spec 039's missing state first) and once nothing is queued or running; a blank digest, build version or source_version isn't judged. No view, CSS, JS, build, migration or ADR change: the panel renders summaries and facts generically (FR-4).

Not built (noted in the area doc as an open point): a release that changes config/art_fingerprint.json queues no rebuild by itself; only a refresh does.

Evidence

• Spec 053 v1.0.1 (Fable review, APPROVE WITH CHANGES, folded in), plan (Fable review, APPROVE WITH CHANGES, folded in), implementation review (Opus): SPEC-ALIGNED WITH FOLLOW-UPS, its two test-tightening minors fixed. Recorded in verification.md.
• Test-first per phase; red and green runs are in verification.md. Two characterization examples pin what the scanner does with each kind of drift (AC-4.1, AC-4.2).
• Full bin/ci ran as the pre-push hook on 99afddcd and passed; bin/rspec --dry-run counts 2882 examples.
• Distilled into docs/architecture/catalog-operations.md and scanner.md; two lessons added. The plan's retirement is owed after the merge.

Note: the Co-Authored-By model line in the commits changed mid-run with the harness (earlier commits Sonnet 5.5, the plan commit Opus 5.5); history is not rewritten.

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