Update logger refactor plan with Express handler exception

🤖 Generated with Codebuff
Co-Authored-By: Codebuff <noreply@codebuff.com>

Author: charleslien

plans/logger-refactor-plan.md

@@ -8,14 +8,20 @@ This is a live document. You should update it with any unintutive cases you find
 - Set `cwd: "backend"` to limit search scope
 - Exclude websocket-action.ts files
 
-### Step 2: For each file (except websocket-action.ts)
+### Step 2: For each file (except websocket-action.ts and index.ts)
 
 - Remove the `import { logger }` line
 - Refactor function signature to use single `params` object containing all arguments including `logger: Logger`
 - Import proper type: `import type { Logger } from '@codebuff/types/logger'`
   - Don't manually type as `{ debug: Function; ... }` - will fail typecheck
 - Add destructuring at top of function body to extract params
 
+**Exception: Express Handler Functions**
+- Do NOT refactor handler functions that are directly called from Express routes in index.ts (e.g., `usageHandler`, `validateAgentNameHandler`, `getTracesForUserHandler`, `relabelForUserHandler`)
+- These handlers should keep their traditional Express signature: `(req, res, next)`
+- Instead, wrap them with arrow functions in index.ts that pass logger: `(req, res, next) => handler({ req, res, next, logger })`
+- This avoids breaking Express's middleware signature expectations
+
 ### Step 3: Update all callers
 
 - **Always run full `bun run typecheck`** (not head/tail!) to find ALL errors