Emit artifact diagnostics bundles

[chubes4]

Summary

• Add a generic wp-codebox/artifact-diagnostics/v1 contract for normalized runtime/artifact diagnostics.
• Emit files/diagnostics.json in every Codebox artifact bundle and reference it from manifest, metadata, review evidence, and returned artifact paths.
• Export buildArtifactDiagnostics() so downstream consumers can normalize observation diagnostics without product-specific packet scripts.

Testing

• npm run build
• node --input-type=module -e 'import assert from \"node:assert/strict\"; import { buildArtifactDiagnostics } from \"./packages/runtime-playground/dist/index.js\"; const diagnostics = buildArtifactDiagnostics([{ id: \"obs-1\", type: \"import-report\", observedAt: \"2026-01-01T00:00:00.000Z\", data: { diagnostics: [{ diagnostic_id: \"layout-gap-1\", type: \"layout_fidelity_gap\", severity: \"warning\", message: \"Grid lost\", path: \"index.html\", selector: \".hero\", refs: [{ path: \"files/import-report.json\", kind: \"import-report\" }], source_report: { html: { element_count: 8 } } }] } }]); assert.equal(diagnostics.schema, \"wp-codebox/artifact-diagnostics/v1\"); assert.equal(diagnostics.status, \"reported\"); assert.equal(diagnostics.summary.warning, 1); assert.equal(diagnostics.diagnostics[0].id, \"layout-gap-1\"); assert.equal(diagnostics.diagnostics[0].details.source_report.html.element_count, 8); console.log(\"artifact diagnostics contract smoke passed\")'
• node packages/cli/dist/index.js run --mount ./examples/simple-plugin:/wordpress/wp-content/plugins/simple-plugin --command wordpress.run-php --arg code='echo \"diagnostics smoke\";' --artifacts "$tmpdir" --json plus assertions for diagnosticsPath, metadata.artifacts.diagnostics, and review.evidence.diagnostics
• npm run release:package
• npm run package-distribution-smoke

Notes

• npm run artifact-contract-smoke was attempted but did not return within 10 minutes in this environment. The targeted artifact bundle diagnostics smoke passed.
• An initial parallel run of package-distribution-smoke and release:package conflicted in dist/release/.../playwright; rerunning sequentially passed.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (openai/gpt-5.5)
• Used for: Implemented the generic artifact diagnostics contract, bundle emission, and smoke assertions under Chris's direction on Codebox/Homeboy/SSI ownership boundaries.