Align GATT transport interface

docs/host_dri_rebuild.md

@@ -32,6 +32,17 @@ Design notes:
 - keeps the implementation small for now
 - avoids mixing GATT transport with logic concerns
 
+Implemented behavior:
+
+- keep the same surface shape as CDC:
+  - `Enum`
+  - `Open`
+  - `Close`
+  - `ReadBytes`
+  - `WriteBytes`
+- stay transport-only
+- keep real BLE implementation for a later node
+
 ### Node 2: CDC transport cleanup
 
 Files updated in this step: