TypeScript Rules

Types

• Never use any — use unknown with type guards or explicit types
• Prefer interface for object shapes, type for unions/intersections
• Export types alongside their functions, not from barrel files
• Use satisfies for type-safe object literals: const x = { ... } satisfies Config

Imports

• Use @/ path alias for imports from apps/web/src/
• Group imports: external libs → @/lib/ → relative slice imports
• Use type imports for type-only: import type { Foo } from './types'

Architecture Boundaries

Vertical slice structure (src/features/<slice>/)

• Each slice owns its own server functions, queries, components, and types
• No cross-slice imports — shared code goes in src/lib/
• src/lib/ modules must NOT import from src/features/

File naming

• Server function files: *.server.ts
• Query/hooks files: *.queries.ts
• Component files: PascalCase (e.g., SessionCard.tsx)
• Test files: *.test.ts(x) co-located with source

Error Handling

• Throw typed errors, not strings: throw new Error('message')
• Use discriminated unions for result types: { ok: true; data: T } | { ok: false; error: string }
• Catch unknown, narrow with instanceof

Functions

• Prefer named function declarations over arrow functions for top-level exports
• Use explicit return types on exported functions
• Keep functions small — max ~50 lines

Zod

• Validate all external input (API responses, form data, URL params) with Zod
• Co-locate schemas with server functions, not in separate schema files
• Use z.infer<typeof schema> for derived types