Instruction file imported from devdaviddr/fullstack-firebase-react-express-template (.github/instructions/typescript.instructions.md). Copyright stays with the author.

TypeScript Guidelines

• Enable and respect strict mode — no implicit any, no non-null assertions (!) unless the null/undefined case is provably impossible.
• Use unknown + type-guard (instanceof, typeof, Zod .safeParse) instead of casting to any.
• Prefer interfaces for object shapes that will be extended; use type aliases for unions, intersections, and mapped types.
• All async functions must be fully await-ed — never fire-and-forget unless a deliberate side-effect comment explains why.
• Public functions and exported types must have JSDoc /** */ comments on the why, not just what.
• Avoid re-exporting everything with barrel index.ts files; import directly from the source file to keep tree-shaking effective.
• Use satisfies or explicit return types on exported functions so callers get precise inference.

Client (packages/client/src)

• Components: named export for utilities/hooks; default export only for page/route-level components.
• Hooks (useXxx): one concern per hook; keep side-effects (useEffect) inside the hook, not in the component.
• Never call getIdToken() at component render time — call it inside a React Query queryFn only (see api/hooks.ts → useMe).
• Tailwind: use utility classes directly; avoid @apply in CSS unless reusing a multi-class pattern 3+ times.

Server (packages/server/src)

• Every async Express handler must end in try/catch → next(err) or be wrapped in an async error-forwarding helper.
• Import config exclusively from config.ts; never read process.env directly in feature code.
• Validate all incoming request bodies with zod before touching req.body.
• Layer boundary: controllers import from services; services import from repositories; cross-layer imports are forbidden.