fix: normalize MCP tool error formatting

AGENT_HANDOFF.md

@@ -105,9 +105,20 @@ Four additional MCP tools registered on the server (`src/server.js`):
 - All handlers use existing modules only (no new imports or files).
 - SDK quirk: `isError: true` wraps results in JSON-RPC error envelope (`code: -32603`).
 
+### Task 5.4 - Normalize MCP tool error formatting ✅
+
+MCP tool error formatting normalized in `src/server.js`. All 5 tool registrations now produce a single "Error:" prefix — no more duplicate `"Error: Error:"` strings.
+
+**Changes:** Each tool callback normalizes the error text before returning:
+- If `result.error` already starts with `"Error:"`, it is used as-is.
+- Otherwise, `"Error: "` is prepended.
+- `result.ok` responses are unchanged.
+
+Smoke tests: npm test 523 passed ✅ · tools/list 5 tools ✅ · ask_chatgpt single prefix ✅ · review_plan single prefix ✅
+
 ## Next Pending
 
-### Task 5.4 - Normalize MCP tool error formatting
+### Task 5.5 - Claude Code MCP configuration and local end-to-end setup
 
 ## General Rules