error-handling-patterns {Backend} (v1.0)

"Firebase Functions are your backend. Design them like microservices, deploy them like magic."

Purpose

Centralized error handler. Custom error classes. Cloud Logging. Error reporting. Cloud Monitoring alerts. [EXPLICIT] When to use: Backend development within Firebase/Google ecosystem.

Core Principles

1. Law of Functions: Each Cloud Function does ONE thing. Single responsibility. [EXPLICIT]
2. Law of Cold Start: Minimize dependencies. Use lazy imports. Set min instances for critical functions. [EXPLICIT]
3. Law of Security: Every HTTP function verifies Firebase ID tokens. No public endpoints without auth. [EXPLICIT]

Core Process

Phase 1: Design

1. Map requirements to Cloud Functions triggers (HTTP, Firestore, Auth, Storage, scheduled). [EXPLICIT]
2. Define input/output contracts for each function. [EXPLICIT]
3. Design error handling and retry strategy. [EXPLICIT]

Phase 2: Implement

1. Create function with proper trigger type. [EXPLICIT]
2. Add auth middleware for HTTP functions. [EXPLICIT]
3. Implement business logic with error handling. [EXPLICIT]
4. Add Cloud Logging for observability. [EXPLICIT]

Phase 3: Test + Deploy

1. Test with Firebase Emulator Suite. [EXPLICIT]
2. Deploy with firebase deploy --only functions. [EXPLICIT]
3. Verify in Firebase Console. [EXPLICIT]

3. Inputs / Outputs

Input	Type	Required	Description
Requirements	Text/Spec	Yes	What the function does
Output	Type	Description
--------	------	-------------
Cloud Function code	TypeScript	Deployable function

Validation Gate

• Single responsibility per function
• Auth middleware on HTTP endpoints
• Error handling with Cloud Logging
• Emulator tests pass
• No AWS/Azure services (R-002)

5. Self-Correction Triggers

[!WARNING] IF function has no auth middleware THEN add verifyIdToken check. IF function imports 10+ dependencies THEN split or lazy-load to reduce cold start.

Usage

Example invocations:

• "/error-handling-patterns" — Run the full error handling patterns workflow
• "error handling patterns on this project" — Apply to current context

Assumptions & Limits

• Assumes access to project artifacts (code, docs, configs) [EXPLICIT]
• Requires English-language output unless otherwise specified [EXPLICIT]
• Does not replace domain expert judgment for final decisions [EXPLICIT]

Edge Cases

Scenario	Handling
Empty or minimal input	Request clarification before proceeding
Conflicting requirements	Flag conflicts explicitly, propose resolution
Out-of-scope request	Redirect to appropriate skill or escalate