docs: clarify controller roles and load switching boundaries

docs/ARCHITECTURE.md

@@ -210,3 +210,25 @@ Current Cargo ESP32 GPIO plan:
 - GPIO 21: SSD1306 OLED I2C SDA
 - GPIO 22: SSD1306 OLED I2C SCL
 - GPIO 25: OLED setup/status button
+
+## Role Boundary Summary
+
+See `docs/controller-roles.md` for the authoritative role split.
+
+Committed v1 architecture:
+
+    Dashboard ESP32-S3
+            <-> WiFi / HTTP REST
+    Cargo ESP32 AP
+            <-> control outputs
+    Automotive load-switching layer
+            <-> fused loads
+    Fridge / Starlink / lights / spare outputs
+
+The Cargo ESP32 owns power-system control.
+
+The Dashboard ESP32-S3 renders the touchscreen UI and future vehicle visualization.
+
+For v1, controller-to-dashboard communication is WiFi/HTTP only. ESP-NOW, MQTT, UART, and CAN-between-controllers are not part of the v1 dashboard link.
+
+The load-switching hardware is not finalized. Bosch relays, WUPP-style modules, smart high-side switching, or a future custom PCB remain implementation options until explicitly selected.