Tachi

Patterns for writing actions (MakeAction/MakeAnonAction), using the Postgres DB (Kysely), and migrating Express routes from MongoDB to Postgres in the Tachi server. Use when adding a new mutation, migrating a Mongo-backed router to Postgres, writing action files, or writing tests for actions or routers.

Aggregates Vitest v8/Istanbul coverage across Tachi workspaces via tachi-coverage-tools (manifest, CLI, optional programmatic API). Use when measuring test coverage, reviewing coverage after changes, adding CI gates, registering a new Vitest package, or when the user mentions coverage reports, coverage-final.json, or just coverage-report.

Guidance on using db-formats/ column lists (SELECT_*) and document mappers (To*Document) instead of selectAll() when writing Postgres-backed endpoints in the Tachi server. Use when writing a new endpoint that reads from a Postgres table, adding a new db-formats file, or when working with Kysely selects that need to return API-compatible (v1-mongodb-like) response shapes.

Prefer staticAssertUnreachable in the default branch of switches that must cover every variant of a union, so exhaustiveness is checked at compile time. Use when writing or reviewing switch on discriminated unions, string literal unions, enums, or any switch meant to be exhaustive in the Tachi TypeScript server.

Preserves existing code comments (line, block, JSDoc, region markers) when editing files; does not delete or collapse comments for brevity unless the user asked to remove or update them. Use when editing any source file, refactoring, or applying fixes where comments already exist.