Observability Patterns

In a system with Offline Clients, Edge Workers (Cloudflare), and AI Agents, "It works on my machine" means nothing.

1. The Request ID Chain

Every operation must have a traceable ID.

1. Client Generation: Client generates x-request-id (UUID).
2. Worker Propagation: Cloudflare Worker logs this ID and passes it to the DB middleware.
3. Error Context: If an AppError is thrown, it must include this ID.

2. Structured AppError Logging

When logging errors, never log just the message. Log the Context.

// ✅ Correct Logging Pattern
console.error(
  JSON.stringify({
    level: 'error',
    requestId: ctx.requestId,
    error: error.name,
    code: error.code,
    // Critical for debugging offline sync issues:
    metadata: {
      batchId: data.batchId,
      inputs: truncate(JSON.stringify(data), 1000),
    },
    stack: error.stack,
  }),
)

3. "Health Check" Endpoints for Agents

Agents need to know if the system is healthy before attempting complex actions.

• /api/health: Basic uptime.
• /api/health/sync: Status of the sync queues.
• /api/health/ai: Status of the LLM/Agent provider connections.

4. Distributed Tracing for Sync

The hardest bugs are "Sync Conflicts". Log the Sync Lifecycle:

1. SYNC_START: Device X, 5 items.
2. SYNC_ITEM: Item A (Create Batch). Result: Success.
3. SYNC_ITEM: Item B (Log Feed). Result: Conflict (Version Mismatch).
4. SYNC_END: Success: 4, Fail: 1.

5. Client-Side Telemetry

Since much logic happens offline, the client must store a "Telemtry Buffer". When online, flush this buffer to the server. Key Metric: "Time from Action to Sync" (How long are users offline?)

Related Skills

• error-handling - The AppError class usage
• cloudflare-workers - The logging constraints (standard out)