Save video under batch counting date; fix retention timezone

AGENTS.md

@@ -53,3 +53,17 @@ touch /dev/shm/bytetrack-counter/.reset
 - `.reset` trigger file
 
 Directory auto-created at startup.
+
+## Video recordings
+
+- Recordings are written to `SHM_DIR` as `batch_pending_*.mp4`, confirmed when ayam detected, and moved via `fork()` (non-blocking) to `OUTPUT_DIR/<batch counting_date>/batch_N_HHMMSS.mp4`.
+- The day folder uses the **batch counting date** (today before `DAILY_CUTOFF_TIME`, tomorrow after), forwarded from `BatchStore` through the batch-closed callback — matching the SQLite `counting_date`.
+- Retention cleanup compares day folders with `std::localtime` to match folder naming.
+
+## Source override
+
+```bash
+bytetrack-counter <config.env> --source /tmp/test.mp4      # local file (single pass)
+bytetrack-counter <config.env> --source rtsp://cam:554/x   # live stream
+bytetrack-counter <config.env> -s path  # or --source=path
+```