fix: BUG-21 GPS-speed fallback in server route replay

BUGS.md

@@ -35,11 +35,13 @@ When CLOSED, move the entire entry to Resolved — don't duplicate.
   (`insert_tracking(gps_x, gps_y, speed=None, …)`) — there is no GPS-derived speed fallback, so
   the SPEED column stays NULL and the replay shows 0.0 km/h (`speed_source="gps"`).
 - **Data**: trip #9 has 723 points — 570 with OBD speed, 25 with speed=0, 128 with NULL speed.
-- **Fix (proposed)**:
-  1. GPS-speed fallback in `_log_loop()` — when OBD speed is None/0 but GPS coords exist,
-     compute speed from the previous position (haversine / elapsed time) and log that as SPEED,
-     so the replay shows the real speed (sourced "gps").
-  2. Investigate why the OBD adapter didn't recover for ~20 min (reconnect on stalled reads).
+- **Fix**: mirror the Pi's `route_points` GPS-speed fallback in the server's `get_trip_route()`
+  (`server/modules/db.py`) — when OBD speed is missing, derive speed from the previous point's
+  movement (haversine / elapsed time, ≥8 m, ≤220 km/h) so the replay shows the real speed
+  instead of flatlining at 0 km/h. (The Pi's own replay already did this; only the portal was
+  missing it.)
+- **Follow-up**: investigate why the OBD adapter didn't recover for ~20 min (reconnect on
+  stalled reads).
 
 ---
 

PLAN.md

@@ -2282,10 +2282,10 @@ logged as `BUG-XX` entries in [BUGS.md](./BUGS.md) (BUG-16 onward) and fixed + v
 - **BUG-20 (server trip IDs inflate) — ✅ FIXED**: `trips.id BIGSERIAL` burned sequence values
   on every upsert (recompute after each upload batch). Fixed: sequence clamped to `MAX(id)`
   after each recompute + one-time renumber migration — trips now 1..10, sequence at 10.
-- **BUG-21 (OBD speed dropout mid-drive) — OPEN**: ELM327 stopped returning speed for ~20 min
-  on 2026-08-13 (22:23:50→22:43:41 UTC); Pi logged NULL speed (no GPS-speed fallback), so the
-  replay shows 0 km/h for that stretch. Proposed: GPS-speed fallback in `_log_loop()` + OBD
-  reconnect on stalled reads.
+- **BUG-21 (OBD speed dropout mid-drive) — 🚧 IN PROGRESS**: ELM327 stopped returning speed for
+  ~20 min on 2026-08-13 (22:23:50→22:43:41 UTC). Fix: server `get_trip_route()` now mirrors the
+  Pi's GPS-speed fallback (derive speed from consecutive GPS points when OBD speed is missing),
+  so the portal replay no longer flatlines at 0 km/h. Follow-up: OBD reconnect on stalled reads.
 
 Open items from the drive — fill in as reported:
 - (none clock-related — BUG-17/BUG-18 closed 2026-08-14).

server/modules/db.py

@@ -617,9 +617,20 @@ def get_trip_route(device_id, trip_id):
         lon = float(p[2])
         speed = p[3] or 0
         raw_odo = p[4]
+        speed_source = "obd" if speed > 0 else "gps"
+        # Mirror the Pi's route_points GPS-speed fallback: when OBD speed is
+        # missing (adapter dropout), derive speed from the previous point's
+        # movement so the replay doesn't flatline at 0 km/h while the car moves.
+        if speed <= 0 and prev is not None:
+            seconds = (p[0] - prev[2]).total_seconds()
+            if seconds > 0:
+                dist_km = hav(prev[0], prev[1], lat, lon)
+                seg_speed = dist_km / seconds * 3600
+                if seg_speed <= 220 and dist_km * 1000 >= 8:
+                    speed = seg_speed
         if prev is not None:
             cumulative += hav(prev[0], prev[1], lat, lon)
-        prev = (lat, lon)
+        prev = (lat, lon, p[0])
         if raw_odo is not None and float(raw_odo) > 0:
             odometer = float(raw_odo)
         else:
@@ -628,10 +639,10 @@ def get_trip_route(device_id, trip_id):
             "datetime": p[0].isoformat(),
             "latitude": lat,
             "longitude": lon,
-            "speed": speed,
+            "speed": round(speed, 1),
             # Mirror the Pi's route_points: OBD speed when we have it,
             # otherwise the point is sourced from GPS.
-            "speed_source": "obd" if speed > 0 else "gps",
+            "speed_source": speed_source,
             "odometer": round(odometer, 1),
         })
     return {