Document watchdog deployment status

Co-authored-by: Copilot <[email protected]>

PLAN.md

@@ -748,7 +748,7 @@ all in `modules/app_obd.py` / `modules/app_events.py`:
   `active`, `/` returned HTTP 200, and the log showed four autonomous reconnect attempts with the
   correct "ELM327 handshake succeeded, but the car ECU did not respond" diagnosis and no traceback.
 
-### Phase 14: Power-loss resilience & watchdog — 🚧 PLANNED
+### Phase 14: Power-loss resilience & watchdog — 🟡 PARTIAL (watchdog done; filesystem/shutdown deferred)
 **New phase, not code-dependent on anything else — OS/hardware-level, can be done anytime,
 ideally before the Pi lives in the car full-time.** A car cuts power abruptly at every key-off;
 nothing in the project currently protects against that, and repeated unclean power loss is a
@@ -767,6 +767,19 @@ classic cause of SD card corruption on embedded Pi projects. Two complementary a
   `RuntimeWatchdogSec`/`watchdog-device` support) so a fully hung app or kernel gets a hard reboot
   automatically instead of sitting dead in the car until someone notices.
 
+**Implemented 2026-08-09**:
+- Added `deploy/yaris-watchdog.conf` with systemd's hardware watchdog set to 10 seconds and
+  `deploy/install_watchdog.sh` to install, activate, and verify it. Deployed to the Pi; confirmed
+  `/dev/watchdog0` is the Broadcom BCM2835 watchdog and systemd reports
+  `RuntimeWatchdogUSec=10s`.
+- Rebooted the Pi and verified the watchdog setting persisted, systemd returned to `running`,
+  `yaris-obd.service` returned to `active`, and `/` returned HTTP 200 after startup.
+- **Explicitly deferred by user decision**: read-only root/filesystem hardening and clean-shutdown
+  hardware. The current 59GB root partition fills the SD card and contains 28GB of dashcam data,
+  so overlay root needs a separate persistent writable storage decision first; shrinking the live
+  mounted root filesystem is not safe. Clean shutdown likewise needs delayed-power or
+  ignition-sense hardware before software can implement it.
+
 ### Phase 15: UI design-system foundation — 🚧 PLANNED
 **New phase, pulled forward from the old "do the whole redesign at the end" plan.** Building the
 Phase 16/17 file browsers (and later the trip-history/Pi-health/settings pages) against the