refactor(devices): route ESP-NOW client through SerialTransport

Drops the direct pyserial imports from espnow_client/espnow_provider
in favor of open_transport/list_serial_ports/port_exists. The gateway
protocol is write-only, so no read() extension was needed. ESP-NOW
gateways are now reachable via usb:VID:PID URLs on Android.

TODO.md

@@ -34,19 +34,18 @@ Build the Android APK automatically on push/tag.
 
 ## Android Root Capture (No Permission Dialog, No System Indicator)
 
-MediaProjection shows a mandatory system overlay/indicator while capturing — unavoidable on stock Android. Many cheap Android TV boxes ship pre-rooted, so an alternative root-only path would give much better UX.
+MediaProjection shows a mandatory system overlay/indicator while capturing — unavoidable on stock Android. Many cheap Android TV boxes ship pre-rooted, so an alternative root-only path gives much better UX.
 
-- [ ] Detect root at runtime: check for `su` binary, `Superuser.apk`, etc.
-- [ ] Implement `SurfaceControlCaptureEngine` (new capture engine) using hidden `SurfaceControl.screenshot()` API via reflection
-  - No permission dialog
-  - No system capture indicator
-  - Direct bitmap output (no encoder/decoder roundtrip)
-- [ ] Engine priority: higher than MediaProjection when root detected
-- [ ] Fallback chain: `SurfaceControl` (root) → `MediaProjection` (stock) → `adb screencap` (last resort)
-- [ ] Handle Android version differences in `SurfaceControl` API surface (renamed/moved across API 29, 30, 33)
-- [ ] Alternative: shell out to `screenrecord --output-format=h264 -` as root (same H.264 decode as scrcpy_client_engine, but local instead of remote ADB)
+- [x] Root detection — `Root.kt` checks common `su` binary paths and, on demand, runs `su -c id` to actually prove UID 0. First call triggers Magisk's grant dialog; grant is cached per session. Exposed to Python via Chaquopy.
+- [x] `RootScreenrecord.kt` — spawns `su -c screenrecord --output-format=h264 --size=WxH -`, feeds the H.264 stdout through a MediaCodec decoder whose output Surface is wired into an ImageReader (RGBA_8888, row-stride-aware). Decoded frames reach the Python pipeline via `PythonBridge.pushRootFrame`.
+- [x] Python-side `RootScreenrecordEngine` (`core/capture_engines/root_screenrecord_engine.py`) mirrors `MediaProjectionEngine` with `ENGINE_PRIORITY=110` (> MediaProjection's 100) so the factory picks it automatically when available.
+- [x] `MainActivity` tries `Root.requestGrant()` before launching the MediaProjection consent flow — on rooted devices the consent dialog is skipped entirely. `CaptureService` has a `createRootIntent()` entry point that bypasses the MediaProjection path.
+- [x] Fallback: if `Root.requestGrant()` returns false (no root, user denied, or `su` timeout) the existing MediaProjection flow runs unchanged.
+- [ ] Real-hardware test pending — need to verify on the user's Magisk'd TV box that: (1) grant dialog appears once, (2) frames actually flow through MediaCodec without the Android 14 capture indicator showing, (3) stop/start cycle terminates the `su` process cleanly.
+- [WONTDO] `SurfaceControl.screenshot()` via reflection — renamed/moved across API 28/29/30/33, hidden-API blocklist varies by release, even rooted apps hit it; days of maintenance for a marginal latency win over the screenrecord path. Not worth it.
+- [WONTDO] `adb screencap` fallback — full-PNG-per-frame pipeline is slower than MediaProjection, no value as a last resort.
 
-Known projects using this approach for reference: scrcpy-hidden-api, shizuku, commercial scrcpy-derived apps.
+Known projects using the screenrecord approach for reference: scrcpy (over ADB), scrcpy-hidden-api, shizuku.
 
 ## Android USB Serial Support
 
@@ -60,7 +59,7 @@ Drive USB LED controllers (APA102, WS2812) connected directly to the Android TV
 - [ ] Real-device test pending — no USB-serial hardware on dev machine. Need to verify on a TV box with CH340, CP2102, or FTDI adapter.
 - [ ] Document supported USB LED controllers in README (once real-device test passes).
 - [ ] Optional: auto-launch the app when a known USB-serial adapter is plugged in (intent-filter on `USB_DEVICE_ATTACHED` + `res/xml/device_filter.xml`). Skipped in v1 — users can just open LedGrab and hit "Discover".
-- [ ] ESP-NOW client (`espnow_client.py` / `espnow_provider.py`) still imports `pyserial` directly and needs bidirectional reads — separate refactor to extend the transport with `read()` if ESP-NOW-via-USB on Android is needed.
+- [x] ESP-NOW client (`espnow_client.py` / `espnow_provider.py`) now routes through `SerialTransport` — `open_transport()` for the gateway serial link, `list_serial_ports()` + `port_exists()` for discovery/validation. Works transparently with `usb:VID:PID` URLs on Android. (Gateway protocol is write-only, so no `read()` extension was needed after all.)
 
 ## Performance Metrics Abstraction