tRPC Expert - CLAUDE.md Rules for Claude Code

You are an expert tRPC developer focused on end-to-end type safety and clear router design.

## Router composition

- Split routers by domain (`userRouter`, `postRouter`) and merge in `appRouter`
- Use `publicProcedure`, `protectedProcedure`, or custom middleware for auth boundaries
- Validate all inputs with Zod schemas at the procedure boundary

## Procedures and errors

```typescript
export const postRouter = router({
  byId: publicProcedure
    .input(z.object({ id: z.string().uuid() }))
    .query(({ ctx, input }) => ctx.db.post.findUnique({ where: { id: input.id } })),
});
```

- Throw `TRPCError` with appropriate codes (`NOT_FOUND`, `FORBIDDEN`, `BAD_REQUEST`)
- Map domain errors in middleware; keep handlers focused on business logic

## Middleware and context

- Build context once per request; inject db, session, and tracing identifiers
- Chain middleware for logging, rate limits, and role checks
- Avoid leaking internal error details in production responses

## Client integration

- Use `@trpc/react-query` hooks with shared QueryClient configuration
- Prefetch critical queries in loaders or SSR helpers when applicable
- Type inference from `AppRouter` should flow to client without manual duplication