feat: introduce device plugin runtime boundary

plugins/xgrids-k1/README.md

@@ -1,9 +1,16 @@
 # XGRIDS / LixelKity K1 plugin
 
-This directory is the target package boundary for the first Mission Core device
-plugin. The verified implementation remains temporarily in `src/k1link` so the
+This directory is the package boundary for the first Mission Core device
+plugin. It now owns the canonical v1alpha manifest
+[`plugin.manifest.json`](plugin.manifest.json). The statically linked frontend
+contribution lives in `apps/control-station/src/device-plugins/xgrids-k1/`; the
+verified backend implementation remains temporarily in `src/k1link` so the
 real-device path stays operational during extraction.
 
+The v1alpha1 host deliberately assigns one model to one plugin runtime, so this
+manifest exposes only `xgrids.lixelkity-k1`. Adding another device model means a
+new plugin contribution until session/model routing lands in the next SDK.
+
 The plugin owns:
 
 - BLE discovery hints and K1 GATT metadata;
@@ -24,3 +31,21 @@ The plugin does not own:
 Until extraction is complete, `src/k1link` is the compatibility source of
 truth and every move into this package must preserve replay and real-device
 acceptance.
+
+Mission Core imports this plugin only from
+`apps/control-station/src/composition/devicePlugins.ts`. The generic shell never
+branches on this plugin ID or reads `k1_ip`, BLE candidates, MQTT topics, or
+other vendor state.
+
+Backend startup loads the reviewed factory declared by `backendEntrypoint`, then
+cross-checks its plugin ID and complete action set against this manifest.
+Actions enter through the host dispatcher and the transitional facade
+`src/k1link/web/xgrids_k1_facade.py`. The old flat routes live in the plugin's
+legacy router; both paths delegate to the same proven
+`XgridsK1CompatibilityService` methods. Synchronous capture/runtime operations
+run outside the FastAPI event loop.
+
+Model switching calls the plugin deactivation hook and must receive a successful
+`stream.stop` before Mission Core removes this custom UI. BLE, MQTT, codec and
+evidence modules remain in `src/k1link` until replay parity and another physical
+K1 regression are complete.