Harden BLE host link and expose latency tools in the dashboard.

Add BLE RTT/stream tests and live tick median in the UI, fix concurrent WebSocket writes and late BATTERY replies, and skip 2M PHY updates that assert under ESP-NOW coexistence.

Co-authored-by: Cursor <cursoragent@cursor.com>

goTool/docs/API_REST.md

@@ -140,6 +140,20 @@ Dashboard WebSocket state includes `host_connected`, `host_transport`, `host_end
 
 **OTA** (`POST /api/ota`) returns **400** unless `transport==uart` and connected.
 
+### BLE latency tests (BLE host only)
+
+```http
+POST /api/ble-rtt
+{"count":50,"warmup":5,"settle_s":0}
+→ {"success":true,"count":50,"warmup":5,"stats":{"n":50,"min_ms":…,"median_ms":…,"mean_ms":…,"max_ms":…}}
+
+POST /api/ble-stream
+{"count":50,"period_ms":16,"tol_ms":2,"timeout_s":15,"client_id":0}
+→ {"success":true,"received":50,"requested":50,"window_ok":true,"dt_esp_ms":{…},"dr_pc_ms":{…},…}
+```
+
+Pauses dashboard/API polling while running. Requires active BLE host (`DIP8=1`).
+
 ### Live stream (host `CACHE_STATUS` poll ~16 ms; BLE uses `BLE_STREAM_TICK`)
 
 ```http