add-package-feature - SKILL.md Agent Skill

name: add-package-feature description: Add a new feature to an existing @fabrk/* package following monorepo conventions user-invocable: true

Add Package Feature

Add a new feature to an existing @fabrk/* package following the monorepo's conventions.

Arguments

package: The package name (e.g., "ai", "auth", "core")
feature: Description of the feature to add

Workflow

Step 1: Understand the Package

Read packages/{package}/src/index.ts to understand existing exports and patterns. Read packages/{package}/package.json for dependencies.

Step 2: Check for Existing Patterns

Look at similar features in the same package. Follow the established patterns:

Adapter pattern: External services behind interfaces from @fabrk/core
Store pattern: Injectable stores with in-memory defaults
Web Crypto API: No Node.js crypto — use Web Crypto for edge compatibility
Callback props: Components accept callbacks, not direct API calls
Zod validation: Use z.input<> for params, z.infer<> for internal types

Step 3: Write Tests First (TDD)

Create test file at packages/{package}/src/{feature}.test.ts. Write failing tests that define the expected behavior. Run: cd packages/{package} && npx vitest run {feature}.test.ts

Step 4: Implement

Create feature file at packages/{package}/src/{feature}.ts. Implement the minimum code to pass all tests.

Step 5: Export

Add to packages/{package}/src/index.ts:

export * from './{feature}'

Step 6: Build & Verify

pnpm build          # All 20 packages must build
pnpm type-check     # All 25 must pass
pnpm test           # All tests must pass

Step 7: Cross-Package Impact

If the feature is used by other packages, check dependents still build:

pnpm build --filter="...@fabrk/{package}"

Step 8: Changeset

pnpm changeset

Select the package, choose patch/minor/major, write description.