feat: initialize cold display guard

task_plan.md

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+# Cold Display Guard Task Plan
+
+## Goal
+
+Create an independent git project under `~/Code` for monitoring food batches in a refrigerated display cabinet. The system tracks each configured display zone, starts a batch timer when food appears, ends it when the zone clears, and raises compliance alerts for over-3-hour removal without trash disposal or for over-3-hour food being put back.
+
+## Confirmed Decisions
+
+- The trash bin is visible in the same camera frame.
+- The display cabinet starts as a 4-column by 2-row layout, but zones must be configurable.
+- A zone may contain multiple food items.
+- Items in the same zone are treated as one batch.
+- Mixed batches are not allowed; a zone must clear before a new batch can start.
+- The first implementation is a standalone project, not a modification of `store_dwell_alert`.
+
+## Phases
+
+| Phase | Status | Notes |
+| --- | --- | --- |
+| Create project skeleton | complete | Built under `~/Code/cold_display_guard`. |
+| Write design and implementation plan | complete | Saved in `docs/plans/`. |
+| Implement core state engine | complete | Pure Python, no camera dependency. |
+| Add config, CLI, README | complete | TOML config and JSONL event CLI skeleton. |
+| Add tests | complete | `python3 -m unittest discover -s tests -v` passes. |
+| Initialize git and commit | complete | Independent repository created. |
+
+## Errors Encountered
+
+| Error | Attempt | Resolution |
+| --- | --- | --- |
+| Ended batches reported `0` dwell seconds | First `unittest` run | Calculate dwell seconds before assigning `ended_at`. |