if(!updated)thrownewAppError('Profile not found',ErrorCodes.PROFILE_NOT_FOUND,404);
returnupdated;
}
```
### Step 3: Route
Routes must return a single type (or a response shape whose `data` is a single type). If multiple shapes are needed, use separate endpoints or a keyed structure (e.g. `data` indexed by a key) so clients get one type per endpoint or key. Do not return a union of shapes from one route based on query parameters.
```typescript
// apps/api/src/routes/account/account.ts
exportconstaccountRouter=newHono().put(
'/user',
authMiddleware,
zValidator('json',ZUpdateProfile),
async(c)=>{
try{
constuser=c.get('user')!;
constdata=c.req.valid('json');
constresult=awaitupdateUser(user.id,data);
returnc.json({success: true,data: result});
}catch(error){
returnhandleError(c,error,'Failed to update profile');
Define all request and response-related types in the feature’s `utils/types.ts` file. **Do not define types or interfaces in `.svelte.ts` files** (e.g. `api/*.svelte.ts` or `store/*.svelte.ts`). Infer types from the API: request type from the RPC call, then success/data from the response type.
For response shapes that need a small normalization (e.g. API returns `JSONValue`, app needs `Record<string, number>`), derive a normalized type in `types.ts` from the success `data` type (e.g. `Omit<Data, 'roleMapping'> & { roleMapping: Record<string, number> }`).
**Do not export custom types from `apps/api/src/rpc-types.ts`.** Only re-export Hono client types (e.g. `InferRequestType`, `InferResponseType`) and the typed client (`Client`, `hcWithType`). All feature-specific types belong in the dashboard's feature `utils/types.ts`, inferred from the API.
### API Class Pattern
API classes handle all logic; components should be thin.
### Translations (UI copy)
- No hardcoded user-facing text in components.
- Strings live in `apps/dashboard/src/lib/utils/translations/en.json`.
- Use `$t('key.path')` in markup and `t('key.path')` in script.
- Use translation keys directly (e.g. `snackbar.success('snackbar.profile.updated')`).
- Only use `t(...)` when combining keys or building dynamic strings.
Outside Svelte components:
- Use `t.get('key.path')` inside plain functions or utilities.
### Utility Functions Pattern
- Extract reusable transformations to `apps/dashboard/src/lib/features/{domain}/utils/{feature}-utils.ts`.
- Keep functions pure and accept all required data as parameters.
### Svelte store binding
You can bind form controls directly to a writable store’s properties. Svelte compiles `bind:value={$store.someProp}` so that reads come from the store and writes go back through the store (via `set`/`update`). Prefer this over duplicating state in the component and syncing with `$effect` (which can cause infinite loops or redundant updates).
In Svelte 5, the built-in `Set` and `Map` classes are **not** reactive. Use `SvelteSet` and `SvelteMap` from `svelte/reactivity` instead. They are already reactive on their own — do **not** wrap them in `$state()`.
```svelte
<scriptlang="ts">
import{SvelteSet}from'svelte/reactivity';
letselectedIds=newSvelteSet<string>();
// Mutations are reactive — no clone-and-reassign needed
Use `.server.ts` files for server-side code to isolate API keys.
### UI Components
- Add new UI components under `packages/ui/src` following existing folder patterns.
- Document component usage and props in `packages/ui/README.md`.
- Add example usages and variants in Storybook stories under `packages/storybook/src`.
- See `packages/ui/README.md` and `packages/storybook/README.md` for full guidance.
- For dashboard forms, prefer `@cio/ui/custom/*-field` wrappers (for example `InputField`, `TextareaField`, `CheckboxField`) so label/error/spacing behavior stays consistent.
- Use base primitives (`@cio/ui/base/input`, `@cio/ui/base/textarea`, `@cio/ui/base/checkbox`, `@cio/ui/base/label`) only when creating/updating reusable UI components or when no custom field wrapper exists.
- In app-level form UIs, do not introduce native form controls (`<input>`, `<textarea>`, `<label>`) when equivalent `packages/ui` components exist.
- **Theme color classes:** Classes that use colors from `packages/ui/src/index.css` (e.g. `text-muted-foreground`, `text-primary`) must be prefixed with `ui:` in dashboard code so they resolve against the UI theme (e.g. `ui:text-muted-foreground`, `ui:text-primary`). Only color-related utilities need the prefix; layout/sizing classes like `rounded`, `border`, `p-4` stay unprefixed (Tailwind defaults).
## Best Practices Summary
### ✅ DO
- Use `AppError` with error codes and status codes
- Handle transactions in services
- Use `handleError` utility in route catch blocks
- Validate with Zod on both client and server
- Define request types in `{domain}/utils/types.ts` for reusability
- Use `this.execute<RequestType>()` in API classes (never call RPC directly)
- Keep components thin - only render UI and call API methods
- Use `.server.ts` for server-side API calls with API keys
- Use non-null assertion (`!`) for `user` when `authMiddleware` is present
- Put all user-facing copy in translations and reference by key