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

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).