feat: register remaining MCP tools

AGENT_HANDOFF.md

@@ -53,6 +53,8 @@ Total: 139 orchestration-only tests, all passing.
 
 ## Completed (Phase 5)
 
+**All five MCP tools registered:** ask_chatgpt, review_plan, review_code, debug_issue, architecture_review.
+
 ### Task 5.1 - MCP server skeleton ✅
 
 Minimal MCP stdio server in `src/server.js`. MCP initialize handshake succeeds. No tools registered yet.
@@ -78,9 +80,34 @@ Minimal MCP stdio server in `src/server.js`. MCP initialize handshake succeeds.
 
 **Production code (`src/server.js`):** ~39 lines, single `ask_chatgpt` tool registered with MCP via Stdio transport.
 
+### Task 5.3 - Register remaining MCP tools ✅
+
+Four additional MCP tools registered on the server (`src/server.js`):
+
+| Tool | Handler |
+|------|---------|
+| `review_plan` | handleReviewPlan |
+| `review_code` | handleReviewCode |
+| `debug_issue` | handleDebugIssue |
+| `architecture_review` | handleArchitectureReview |
+
+**All five MCP tools now registered:** ask_chatgpt, review_plan, review_code, debug_issue, architecture_review.
+
+**Smoke test results (all passing):**
+- initialize → server returns `chatgpt-mcp` v0.1.0 ✅
+- tools/list → 5 tools total ✅
+- tools/call reaches handlers for all 5 tools ✅
+- missing OPENAI_API_KEY → structured tool errors: `"Error: Configuration error: OPENAI_API_KEY is missing."` ✅
+- npm test → 523 tests pass across 18 test files, no regressions ✅
+
+**Implementation notes:**
+- Each tool registered explicitly with its own `registerTool()` call — no registry abstraction.
+- All handlers use existing modules only (no new imports or files).
+- SDK quirk: `isError: true` wraps results in JSON-RPC error envelope (`code: -32603`).
+
 ## Next Pending
 
-### Task 5.3 - Register remaining MCP tools (review_plan, review_code, debug_issue, architecture_review)
+### Task 5.4 - Normalize MCP tool error formatting
 
 ## General Rules