chore: import upstream snapshot with attribution

rules/typescript/coding-style.md

@@ -0,0 +1,199 @@
+---
+paths:
+  - "**/*.ts"
+  - "**/*.tsx"
+  - "**/*.js"
+  - "**/*.jsx"
+---
+# TypeScript/JavaScript Coding Style
+
+> This file extends [common/coding-style.md](../common/coding-style.md) with TypeScript/JavaScript specific content.
+
+## Types and Interfaces
+
+Use types to make public APIs, shared models, and component props explicit, readable, and reusable.
+
+### Public APIs
+
+- Add parameter and return types to exported functions, shared utilities, and public class methods
+- Let TypeScript infer obvious local variable types
+- Extract repeated inline object shapes into named types or interfaces
+
+```typescript
+// WRONG: Exported function without explicit types
+export function formatUser(user) {
+  return `${user.firstName} ${user.lastName}`
+}
+
+// CORRECT: Explicit types on public APIs
+interface User {
+  firstName: string
+  lastName: string
+}
+
+export function formatUser(user: User): string {
+  return `${user.firstName} ${user.lastName}`
+}
+```
+
+### Interfaces vs. Type Aliases
+
+- Use `interface` for object shapes that may be extended or implemented
+- Use `type` for unions, intersections, tuples, mapped types, and utility types
+- Prefer string literal unions over `enum` unless an `enum` is required for interoperability
+
+```typescript
+interface User {
+  id: string
+  email: string
+}
+
+type UserRole = 'admin' | 'member'
+type UserWithRole = User & {
+  role: UserRole
+}
+```
+
+### Avoid `any`
+
+- Avoid `any` in application code
+- Use `unknown` for external or untrusted input, then narrow it safely
+- Use generics when a value's type depends on the caller
+
+```typescript
+// WRONG: any removes type safety
+function getErrorMessage(error: any) {
+  return error.message
+}
+
+// CORRECT: unknown forces safe narrowing
+function getErrorMessage(error: unknown): string {
+  if (error instanceof Error) {
+    return error.message
+  }
+
+  return 'Unexpected error'
+}
+```
+
+### React Props
+
+- Define component props with a named `interface` or `type`
+- Type callback props explicitly
+- Do not use `React.FC` unless there is a specific reason to do so
+
+```typescript
+interface User {
+  id: string
+  email: string
+}
+
+interface UserCardProps {
+  user: User
+  onSelect: (id: string) => void
+}
+
+function UserCard({ user, onSelect }: UserCardProps) {
+  return <button onClick={() => onSelect(user.id)}>{user.email}</button>
+}
+```
+
+### JavaScript Files
+
+- In `.js` and `.jsx` files, use JSDoc when types improve clarity and a TypeScript migration is not practical
+- Keep JSDoc aligned with runtime behavior
+
+```javascript
+/**
+ * @param {{ firstName: string, lastName: string }} user
+ * @returns {string}
+ */
+export function formatUser(user) {
+  return `${user.firstName} ${user.lastName}`
+}
+```
+
+## Immutability
+
+Use spread operator for immutable updates:
+
+```typescript
+interface User {
+  id: string
+  name: string
+}
+
+// WRONG: Mutation
+function updateUser(user: User, name: string): User {
+  user.name = name // MUTATION!
+  return user
+}
+
+// CORRECT: Immutability
+function updateUser(user: Readonly<User>, name: string): User {
+  return {
+    ...user,
+    name
+  }
+}
+```
+
+## Error Handling
+
+Use async/await with try-catch and narrow unknown errors safely:
+
+```typescript
+interface User {
+  id: string
+  email: string
+}
+
+declare function riskyOperation(userId: string): Promise<User>
+
+function getErrorMessage(error: unknown): string {
+  if (error instanceof Error) {
+    return error.message
+  }
+
+  return 'Unexpected error'
+}
+
+const logger = {
+  error: (message: string, error: unknown) => {
+    // Replace with your production logger (for example, pino or winston).
+  }
+}
+
+async function loadUser(userId: string): Promise<User> {
+  try {
+    const result = await riskyOperation(userId)
+    return result
+  } catch (error: unknown) {
+    logger.error('Operation failed', error)
+    throw new Error(getErrorMessage(error))
+  }
+}
+```
+
+## Input Validation
+
+Use Zod for schema-based validation and infer types from the schema:
+
+```typescript
+import { z } from 'zod'
+
+const userSchema = z.object({
+  email: z.string().email(),
+  age: z.number().int().min(0).max(150)
+})
+
+type UserInput = z.infer<typeof userSchema>
+
+const validated: UserInput = userSchema.parse(input)
+```
+
+## Console.log
+
+- No `console.log` statements in production code
+- Use proper logging libraries instead
+- See hooks for automatic detection