Document Phase 6 on-device verification for FB-10/FB-11

docs/feedback/FB-11-route-planner-tiles-still-blank.md

@@ -247,3 +247,25 @@ this change (no new issues introduced; the new constructor parameter needed its
 in `telemetry_uploader.dart`, to avoid adding a 5th). `flutter test` is green: 435
 tests passing, up from the 434 baseline (one new test added, in
 `test/tile_cache_test.dart`).
+
+### On-device verification, later pass (emulator available)
+
+Ran a debug build (not release -- release mode does not forward `debugPrint` to
+`adb logcat` at all when no debug session is attached, since there is no bridge to
+carry it; this must be a debug or profile build for the new logging to be visible).
+Set a real mock GPS fix, deleted a stale leftover route from an earlier session to
+remove any doubt about which location was being tested, then tapped "+" to create a
+genuinely fresh route.
+
+**The blank-map bug is confirmed fixed.** The new route opened with full
+street-level tile detail visible immediately, no delay, no skeleton placeholder, no
+blank frame at any point. Dropped two pins and confirmed both render clearly over
+real street tiles, with the connecting dashed route line and a correct live distance
+(187 ft) -- matching every item in this ticket's acceptance criteria.
+
+Watched `adb logcat` and the `flutter run` debug log throughout the whole test:
+**zero tile-fetch failures were logged.** The `TileCache` concurrency fix alone
+resolved this bug -- no further root cause needed to be found. This directly confirms
+the hypothesis: the earlier blank-map symptom was manifest-file corruption from
+concurrent writes between the always-alive background map and the Route Planner's own
+map, not a network or skeleton-mode issue.