Classify bounded article image-well geometry evidence

[chubes4]

Summary

Extend the existing layout geometry proof export with a source-derived discriminator for article image wells, making eligible geometry easier for downstream imports to identify and edit while retaining the existing bounds and overlap protections.

What changed

• Classify accepted reductions as `article_image_well` when the target is an `img` or `picture` within an `article`; retain `generic` for all other reductions.
• Preserve existing source-path and source-hash identification, viewport and candidate bounds, and non-overlapping reduction selection.
• Add regression coverage for the article image-well classification and document the exported discriminator.

How to test

1. Run npm test -- src/lib/screenshot/layout-geometry-proof.test.ts; expect passes as recorded by Cook's deterministic gate.

Compatibility

Additive proof-schema content: consumers can use the new `kind` discriminator, while existing node evidence and generic classifications remain available. Runtime change is limited to classification based on the final exported DOM; it does not change capture selection or geometry acceptance. Source relationship: existing layout-geometry proof pipeline. Change kind: additive export metadata. Verification capability: focused test and diff checks. Evidence boundary: only accepted reductions targeting `img` or `picture` inside an `article` receive the image-well label.

Evidence

• Verified command npm test -- src/lib/screenshot/layout-geometry-proof.test.ts: status=succeeded; candidate commit 5d13ad731b293dd926600a6acb38a8f830673841, tree 9c2b5ae6e57bc829b4a8414c30efb2ed95f83fc3, fingerprint 73b99c294dca7c750588871dc8be7f1c1603708cf33d46587838aa7583b0a78c; durable gate gate-1
• Base unchanged since verification: main remains at 8bf92c3.
• CI expected: Homeboy CI after push
• Candidate adoption provenance: the candidate was promoted from the recorded Cook task execution.
• Cook deterministic verification: 1 gate(s) completed green.
• Durable run execution: Succeeded
• Reviewer-resolvable evidence from source_refs[0]: Export source-identified image-well geometry for editable imports, beyond redundant wrapper reductions #480
• Task objective: Export bounded source-identified nonredundant article image-well geometry for editable downstream imports
• Verified candidate scope: 3 changed file(s): docs/layout-geometry-proof.md, src/lib/screenshot/layout-geometry-proof.test.ts, src/lib/screenshot/layout-geometry-proof.ts.
• Verified finalization base: main at 8bf92c3
• deterministic gate passed: sh -lc npm test -- src/lib/screenshot/layout-geometry-proof.test.ts (Passed)

AI assistance

• AI assistance: Yes
• Tool(s): Homeboy (opencode)
• Model: openai/gpt-6-luna
• Used for: Inspected the existing capture, proof-export contract, documentation, and tests first; added bounded source-derived classification and regression coverage. `git diff --check` passed. The focused test command was attempted but could not run because Vitest is unavailable in this workspace; this is an observation, not a final gate result. Homeboy runs the declared deterministic gate after harvest.