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

BUGS.md

@@ -8,44 +8,6 @@ When CLOSED, move the entire entry to Resolved — don't duplicate.
 
 ## Open bugs
 
-### BUG-17 — Server trip timestamps wrong after an offline period
-- **Status**: `OPEN` 2026-08-13
-- **Phase**: 29
-- **Symptom**: two trips from the 2026-08-13 drive have bad timestamps on the server:
-  - Trip **25136** — time is wrong.
-  - Trip **25137** — starts 09:59, then jumps to 14:xx after the first point.
-- **Cause (hypothesis)**: the Pi has no RTC, so while offline it runs on a stale
-  `fake-hwclock` time; when NTP later re-syncs, the clock snaps forward, producing the
-  timestamp jump mid-trip. Root cause is BUG-18.
-
-### BUG-18 — Pi needs offline timekeeping (no RTC)
-- **Status**: `IN PROGRESS` 2026-08-14
-- **Phase**: 29
-- **Problem**: the Pi 3 has no real-time clock. Without internet (no NTP) the system clock
-  is wrong across power cycles, corrupting tracking/trip timestamps (BUG-16/BUG-17).
-- **Progress 2026-08-14**: DS3231 module installed + working. Pi config done:
-  `dtparam=i2c_arm=on` + `dtoverlay=i2c-rtc,ds3231` in `/boot/firmware/config.txt`,
-  `i2c-tools` installed, `fake-hwclock` disabled, `i2c-dev` added to `modules-load.d`.
-  The DS3231 now probes at `0x68` (`UU`), its 24C32 EEPROM at `0x57`, `/dev/rtc0` registered,
-  and `hwclock -r` matches system time. (First scan was an empty bus — a data-line wiring
-  issue, since resolved.)
-  **Pending**: power-cycle persistence test — unplug, replug, confirm correct time at boot
-  without NTP. Also: the charge diode was re-added during debugging and must be removed again
-  for the CR2032.
-- **Fix plan (both, they complement each other)**:
-  1. **DS3231 RTC module (primary)** — battery-backed RTC on the free I²C bus (SDA pin 3,
-     SCL pin 5, 3.3V pin 1, GND pin 6). Enable `dtparam=i2c_arm=on` +
-     `dtoverlay=i2c-rtc,ds3231` in `/boot/firmware/config.txt`, install `i2c-tools`, disable
-     `fake-hwclock`. Use a **CR2032** and first **desolder the module's charging resistor +
-     diode** (cheap ZS-042-style boards charge the coin cell — unsafe for a CR2032; the
-     well-known DS3231 charging-circuit issue). Gives correct time instantly at boot, ±2 ppm.
-  2. **SIM868 CR1220 RTC backup (secondary)** — the HAT has a CR1220 holder on the back
-     (item 20). A CR1220 keeps the SIM868's internal RTC alive across power-off, enabling
-     faster GNSS warm starts and letting the Pi optionally read the module time at boot
-     (`AT+CCLK`) as an offline fallback.
-  - Keep `systemd-timesyncd` for online NTP; fall back to the RTC (DS3231) and optionally
-    GNSS time when offline.
-
 ### BUG-19 — Dashboard OBD values slow to appear while the car is running
 - **Status**: `OPEN` 2026-08-13
 - **Phase**: 29
@@ -66,6 +28,29 @@ When CLOSED, move the entire entry to Resolved — don't duplicate.
 
 ## Resolved
 
+### BUG-18 — Pi needs offline timekeeping (no RTC)
+- **Status**: `CLOSED` 2026-08-14
+- **Commit**: `PENDING`
+- **Fix**: DS3231 RTC module installed on the free I²C bus (SDA pin 3, SCL pin 5, 3.3V pin 1,
+  GND pin 6) with a CR2032 (charge diode removed). Pi config: `dtparam=i2c_arm=on` +
+  `dtoverlay=i2c-rtc,ds3231` in `/boot/firmware/config.txt`, `i2c-tools` installed,
+  `fake-hwclock` disabled, `i2c-dev` persisted via `modules-load.d`. CR1220 also installed in
+  the SIM868 HAT holder (secondary RTC backup).
+- **Verification**: DS3231 probes at `0x68` (`UU`), its 24C32 EEPROM at `0x57`, `/dev/rtc0`
+  registered. Power-cycle test passed — after a full unplug/replug the boot log reads
+  `setting system clock to 2026-08-14…` from the RTC (was `2000-01-01` before), and
+  `hwclock -r` matches system time. (Debugging note: the first scans were an empty bus due to
+  a data-line wiring issue, resolved during re-soldering.)
+
+### BUG-17 — Server trip timestamps wrong after an offline period
+- **Status**: `CLOSED` 2026-08-14
+- **Commit**: `PENDING`
+- **Fix**: root cause was BUG-18 — no RTC, so offline the Pi ran on a stale `fake-hwclock`
+  time and NTP snapped the clock forward mid-trip. Fixed by installing the DS3231 (BUG-18).
+- **Verification**: RTC power-cycle test passed (BUG-18). Historical trips 25136/25137 keep
+  their bad timestamps (raw tracking rows were recorded with a wrong clock and can't be
+  retroactively corrected) — future trips will be correct.
+
 ### BUG-15 — Phone can't host the hotspot and connect to the Pi's AP at once
 - **Status**: `CLOSED` 2026-08-13
 - **Commit**: `ab79820`