Implement Check Index Diagnostics

Goal

Implement the shared discovery, check, diagnostics, and in-memory summary projection pipeline for P0.

Sources

• architecture/forma-p0-check-index-spec
• architecture/forma-p0-operation-api-spec
• decisions/forma-p0-core-architecture

Context

P0 no longer writes or requires a committed persistent index file. Operations discover workspace state at runtime and build deterministic in-memory projections for checks, list views, renders, and RPC responses. Diagnostics are runtime operation results and must not be persisted.

In Scope

• Discover spaces, views, entries, and successfully resolved references.
• Build deterministic in-memory summary projections without writing them to disk.
• Implement diagnostic result shape, status values, diagnostic code families, and location objects.
• Ensure unresolved and ambiguous references appear as diagnostics, not resolved refs.
• Add golden JSON fixtures for valid, unresolved-ref, ambiguous-ref, invalid-frontmatter, invalid-config, invalid-view, and path-cases workspaces.

Out Of Scope

• Local full index, SQLite, vector search, filesystem watchers, or incremental indexing.
• Persisted diagnostic result files.
• Automatic repair or fix commands.

Acceptance Criteria

• check builds discovery state in memory and reports diagnostics without writing files.
• No operation writes or requires a persistent index artifact.
• Public JSON contains workspace-relative POSIX paths only.
• Golden tests cover deterministic ordering and exclusion of diagnostics from resolved refs and in-memory projections.

Relationship Notes

Previously blocked by Schema DSL/runtime values and Markdown FormaAST parser; both prerequisites are now done.

Open Questions

• None.