docs: add matching integration tests to high priority tasks

docs/TODO.md

@@ -23,6 +23,18 @@
 - **Impact:** Tier system fairness algorithm depends on accurate karma tracking
 - **Dependencies:** Matches API, Ratings API, Recording Suggestions
 
+**🟡 HIGH: Matching Algorithm Integration Tests**
+- **Issue:** Only unit tests for helper functions exist, no end-to-end tests for `runMatching()`
+- **Test Plan:** `backend/src/__tests__/matching-scenarios.md` (18 scenarios defined)
+- **Priority Phases:**
+  1. **Phase 1:** Fundamentals (TC1-3) - Basic happy path, NOT_FOUND scenarios
+  2. **Phase 2:** Collision Detection (TC4-9) - Buffers, slot mapping
+  3. **Phase 3:** Limits & Workload (TC10-11) - **CRITICAL bug verification** (recording-recording collision)
+  4. **Phase 4:** Fairness & Tiers (TC12-16) - Tier penalties, sorting priority
+  5. **Phase 5:** Edge Cases (TC17-18) - Sanity checks
+- **Impact:** Ensures matching algorithm works correctly end-to-end, verifies critical bug fixes
+- **Status:** Test plan documented, implementation pending
+
 ### Recently Completed (2025-11-29)
 - 3-Tier Account System (BASIC/SUPPORTER/COMFORT) with fairness algorithm
 - Dual Buffer System (prep before + rest after dancing)