docs: close BUG-17 + BUG-18 — DS3231 RTC verified across power loss

PLAN.md

@@ -2272,13 +2272,15 @@ logged as `BUG-XX` entries in [BUGS.md](./BUGS.md) (BUG-16 onward) and fixed + v
   set and local trip building was silently blocked since BUG-10. The flag is now persisted
   across reboots; also fixed a NULL-GPS speed-only row crash in the trip builder. Verified the
   2026-08-13 drive now appears locally.
-- **BUG-17 (trip timestamps wrong) — OPEN**: no RTC → clock drifts without internet.
-- **BUG-18 (no RTC) — 🚧 IN PROGRESS**: DS3231 installed + configured + detected on I²C (`0x68`),
-  `hwclock` reads correct time; `fake-hwclock` disabled; `i2c-dev` persisted. Pending the
-  power-cycle persistence test. Secondary: SIM868 CR1220 RTC backup still to install.
+- **BUG-17 (trip timestamps wrong) — ✅ FIXED**: root cause was BUG-18 (no RTC). Fixed by the
+  DS3231 install; historical trips 25136/25137 keep their bad data, future trips will be correct.
+- **BUG-18 (no RTC) — ✅ FIXED**: DS3231 on I²C (`0x68`) + CR2032 (charge diode removed), config
+  (`dtparam=i2c_arm=on` + `dtoverlay=i2c-rtc,ds3231`), `fake-hwclock` disabled, `i2c-dev`
+  persisted. Power-cycle test passed — boots with correct time from RTC. SIM868 CR1220 also
+  installed (secondary). Optional follow-up: `AT+CCLK` boot-time clock fallback in `app_gps.py`.
 
 Open items from the drive — fill in as reported:
-- BUG-17 (clock) — blocked on BUG-18 power-cycle verification.
+- (none clock-related — BUG-17/BUG-18 closed 2026-08-14).
 
 ## Working Notes / Environment Gotchas