Create a REST API endpoint for user profile updates:
1. Use the existing Express.js pattern from src/routes/users.ts
2. Add zod validation matching src/lib/validators.ts
3. Handle all error cases: missing fields, invalid email, duplicate username
4. Add auth middleware from src/middleware/auth.ts
5. Return consistent error format: { error: string, code: number }

Architect mode: Design a migration from REST to GraphQL for the users module.
1. Map current REST endpoints → GraphQL queries/mutations
2. Identify resolvers needed and what existing services they wrap
3. Plan the schema: types, inputs, enums
4. Consider performance: N+1 risks, DataLoader strategy
5. List what stays the same (auth middleware, database layer)
Do NOT write implementation — architecture plan only.

Debug mode: Users report 500 errors after updating profile images.
1. Check the image upload endpoint in src/routes/upload.ts
2. Trace the file processing pipeline: multer → sharp → S3
3. Check for: file size limits, unsupported formats, S3 permissions
4. Add instrumentation: log file size, format, processing time
5. Reproduce with a 20MB PNG — check what breaks
Report findings before making changes.

Test mode: Generate tests for src/services/billing.ts
1. Read the existing test patterns in src/__tests__/
2. Cover: normal subscription flow, payment failure, proration, cancellation
3. Mock external services (Stripe) using the existing mock helpers
4. Add edge cases: zero-amount invoice, past-due customer, expired card
5. Run tests after generation: npm test -- billing