Generate skill tool schemas in SkillFrontmatterField.fromFrontmatter

[lukemelia]

Restructures the index-time tool schema generation so the schema work lives in SkillFrontmatterField.fromFrontmatter — the type that owns the skill frontmatter schema — instead of a skill-shape-aware stamping pass inside the generic host file extractor. Addresses the review feedback on the base PR; the observable behavior (stamped file-meta, clean search_doc, diagnostics.toolSchemaErrors) is unchanged.

Shape

skills/my-skill/SKILL.md
        │
        ▼  MarkdownDef.extractAttributes (context: { fileURL, toolContext? })
  SkillFrontmatterField.fromFrontmatter
        │  maps name/description/tools (incl. legacy boxel.commands)
        │  and, when the context carries a toolContext, generates each
        │  tool's LLM definition itself (import.meta.loader + card-api +
        │  basicMappings)
        ▼
  { attributes,            → search doc (tools as authored)
    fileMetaAttributes?,   → file-meta resource (tools + definition stamp)
    diagnostics? }         → merged onto the row's diagnostics

• FrontmatterField.fromFrontmatter is now async and returns a structured result; the base implementation is unchanged in behavior. Only the skill subclass does tool work — the extractor no longer inspects kind or the tools array.
• The diagnostics leg of the contract is kind-agnostic: a FrontmatterField subclass contributes a Partial<Diagnostics> bag, and the plumbing (markdown-file-def, the host extractor, the extract response's frontmatterDiagnostics, the file-indexer merge) carries it opaquely. Only SkillFrontmatterField (producer) and the /_indexing-errors surfacing (consumer) name the toolSchemaErrors key.
• The enriched frontmatter and the diagnostics bag travel from extractAttributes to the extractor on the same out-of-band symbol channels the frontmatter parse error uses (FRONTMATTER_FILE_META_VALUE_SYMBOL, FRONTMATTER_DIAGNOSTICS_SYMBOL), so multi-KB definitions still never land in search_doc.
• The file-extract render route mints the owner-carrying ToolContext and threads it through extractAttributes options. Its presence is the gate: host-package tools resolve services through the context's owner at construction, and only the indexing path should pay the module-loading cost — interactive extract paths (room file attach, the store's direct fallback) pass none and skip the work. This replaces the generateToolSchemas boolean the base PR used.
• ToolField's stamped JsonField is renamed tool → definition (per review). Legacy Skill cards' commands entries now serialize with definition: null rather than tool: null.
• Base modules value-import basicMappings from @cardstack/runtime-common/helpers/ai, which needs a loader shim in the host's externals (same lazy pattern as marked-sync).
• Diagnostics row schema and its consumers (indexer merge, /_indexing-errors, boxel-cli formatter) are untouched.

Testing

The existing acceptance coverage (prerender-file-extract-test) exercises the full path — stamping via the render route, search-doc/authored split, broken-tool error attribution, non-skill kinds — and is updated only for the renamed surfaces. Type-check and lint pass across base, host, and runtime-common; host suite runs in CI.

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[github-actions]

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Host Test Results

    1 files  ±0      1 suites  ±0   2h 56m 15s ⏱️ -38s
3 472 tests ±0  3 457 ✅ ±0  15 💤 ±0  0 ❌ ±0 
3 491 runs  ±0  3 476 ✅ ±0  15 💤 ±0  0 ❌ ±0 

Results for commit 2efd971. ± Comparison against earlier commit 1b2f70c.

Realm Server Test Results

    1 files  ±0      1 suites  ±0   11m 20s ⏱️ -9s
1 817 tests ±0  1 817 ✅ ±0  0 💤 ±0  0 ❌ ±0 
1 896 runs  ±0  1 896 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 2efd971. ± Comparison against earlier commit 1b2f70c.