---

name: "implement" description: "Step 5 of the Weft TDD workflow. Use after /unit-test's red phase: replaces the declare mocks with real code in-place, enforces signature parity with the mock surface, and loops vp check --fix → vp run check → vp run test until green. Finishes with graphify update."

/implement: Implementation + green loop (TDD step 5)

Replace the declare mocks with real code, keeping the surface identical, until all checks and tests are green.

When to run

• Previous step: /unit-test (tests exist and a red run is recorded).
• Next step: /e2e.
• Gate (exit): vp run check and vp run test both green, signature parity confirmed, graphify update . run.

Procedure

1. Replace mocks in-place. In the feature's source file, replace each declare statement with its real implementation. Same file, same exports, same signatures. Keep the JSDoc written in /mock (update prose only if behavior details demand it).

2. Implementation standards: Effect patterns throughout, tagged errors (the union declared in /mock), Services/Layers for shared capabilities, Schema at unknown/I-O boundaries, pipe(effect, ...) preferred, Option for optionality, readonly data, explicit type guards. Effect.gen vs pipe by readability. No JSX-style patterns.

3. Signature-parity pass (explicit, not assumed). Diff the implemented exports against the mock surface committed in step 2:

   • No export added, removed, or renamed.
   • No signature changed (parameters, return types, generics, error union).

   Typecheck alone does not catch additions or loosened types. Do this pass deliberately. Any deviation triggers the pause rule: stop implementing, return to /spec and /mock to update spec + surface (and /type-tests + /unit-test if affected), then resume here.

4. Green loop. Repeat until both are clean:

   1. vp check --fix: auto-fix formatting/lint (safe here: packages just packed by the run tasks).
   2. vp run check: pack, then format/lint/typecheck. Must be green.
   3. vp run test: pack, then run all node/jsdom tests. Every test from the red phase must now pass; no other test may regress.

   Never use bare vp check / vp test as validation. They skip pack and report false cross-package errors (the pack rule).

5. Update the knowledge graph: run graphify update . (AST-only, no API cost).

6. Hand off. Next step is /e2e.

Rules

• Implementation must match mock signatures exactly and behavior must match specs.md.
• If implementation reveals mocks/specs need changes, apply the pause rule: update specs and mocks first, never drift silently.
• Fix the implementation to satisfy the tests; changing a test is only legitimate when the pause rule has first changed the spec it encodes.