feat: add lightweight trajectory tracking

progress.md

@@ -199,6 +199,12 @@
 | 2026-05-29 | Phase 1 | Coding Agent | Fixed testing-agent findings | Added target validation, nullable optional fields, and evidence/count double-consume guard |
 | 2026-05-29 | Phase 1 | Testing Agent | Re-tested phase 1 fixes | Verdict pass; no bugs found |
 | 2026-05-29 | Phase 1 | Main Agent | Ran local verification | `tests.test_engine` passed with 24 tests; full Python suite passed with 55 tests |
+| 2026-05-29 | Phase 2 | Main Agent | Marked Phase 2 as `in_progress` | Preparing fresh coding/testing agents for lightweight motion trajectory detection |
+| 2026-05-29 | Phase 2 | Coding Agent | Implemented initial lightweight `TrajectoryTracker` | Target vision tests passed locally, but testing agent found multi-candidate and source-margin risks |
+| 2026-05-29 | Phase 2 | Testing Agent | Reviewed initial trajectory tracker | Verdict fail: single blob can confirm multiple candidates, source margin false positive, diagnostics lack per-candidate reasons |
+| 2026-05-29 | Phase 2 | Coding Agent | Fixed trajectory tracker findings | Added blob consumption, strict source polygon origin, and per-candidate diagnostics |
+| 2026-05-29 | Phase 2 | Testing Agent | Re-tested phase 2 fixes | Verdict pass; no bugs found |
+| 2026-05-29 | Phase 2 | Main Agent | Ran local verification | `tests.test_vision` passed with 20 tests; full Python suite passed with 64 tests; dependency scan had no model/heavy vision matches |
 
 ### Test Results
 
@@ -206,6 +212,9 @@
 | --- | --- | --- | --- |
 | 2026-05-29 | `PYTHONPATH=src python3 -m unittest tests.test_engine -v` | pass | 24 engine tests passed after phase 1 evidence fixes |
 | 2026-05-29 | `PYTHONPATH=src python3 -m unittest discover -s tests -v` | pass | 55 full Python tests passed after phase 1 |
+| 2026-05-29 | `PYTHONPATH=src python3 -m unittest tests.test_vision -v` | pass | 20 vision tests passed after phase 2 trajectory tracker |
+| 2026-05-29 | `PYTHONPATH=src python3 -m unittest discover -s tests -v` | pass | 64 full Python tests passed after phase 2 |
+| 2026-05-29 | `rg -n "ultralytics|torch|onnxruntime|openvino|opencv|cv2|numpy" src tests pyproject.toml` | pass | No matches; command exited 1 because no heavy vision/model dependency was found |
 
 ### Bug Loop
 
@@ -214,6 +223,32 @@
 | Phase 1 | `disposal_evidence` and `trash_deposit_count` can double-consume the same disposal signal | Added regression test and suppress generic trash fallback when confirming source-specific evidence exists in the observation | Resolved; testing agent and local full Python suite passed |
 | Phase 1 | High-confidence evidence with non-trash target can close pending disposal | Added target whitelist for `trash` / `trash_bin` plus regression test | Resolved; testing agent and local full Python suite passed |
 | Phase 1 | `item_class: null` and `detector_score: null` lose null semantics | Changed optional evidence fields to preserve `None` plus regression test | Resolved; testing agent and local full Python suite passed |
+| Phase 2 | Single motion blob can confirm multiple active candidates | Added frame-local blob IDs and consume each sampled blob once per frame | Resolved; testing agent and local full Python suite passed |
+| Phase 2 | Source-zone margin can treat near-outside movement as source-origin movement | Source-origin check now requires strict source polygon containment | Resolved; testing agent and local full Python suite passed |
+| Phase 2 | Trajectory diagnostics only expose aggregate counts | Added `emitted`, `rejected`, and `expired` diagnostic lists with source, reason, point count, confidence, and direction score | Resolved; testing agent and local full Python suite passed |
+
+## 2026-05-29 Phase Completed: Phase 2 - Lightweight Motion Trajectory Backend
+
+Status: complete
+
+Files Changed:
+- `src/cold_display_guard/vision.py`
+- `tests/test_vision.py`
+- `task_plan.md`
+- `progress.md`
+
+Tests:
+- `PYTHONPATH=src python3 -m unittest tests.test_vision -v`: pass
+- `PYTHONPATH=src python3 -m unittest discover -s tests -v`: pass
+- `rg -n "ultralytics|torch|onnxruntime|openvino|opencv|cv2|numpy" src tests pyproject.toml`: pass, no matches
+
+Notes:
+- `TrajectoryTracker` now emits `DisposalEvidence` with `target=trash` and `method=motion`.
+- Tracker uses frame-delta motion blobs, strict source-origin validation, target ROI validation, direction scoring, and per-candidate diagnostics.
+- Multiple candidates cannot reuse the same frame-local blob for confirmation.
+
+Risks:
+- Tracker is implemented but not yet wired into `main.py`; phase 3 will integrate runtime observation, diagnostics, and faster active-candidate sampling.
 
 ## 2026-05-29 Phase Completed: Phase 1 - Data Contract And Engine Evidence Handling