Update CLAUDE.md and fix final Tortoise handler return value

- Add dashboard development commands (just dashboard, mix phx.server)
- Document Dashboard.Application and Dashboard.MqttSubscriber components
- Add comprehensive dashboard section with MQTT configuration details
- Include critical implementation notes for Tortoise handler return values
- Fix handle_message to return {:ok, state} instead of [] to prevent crashes

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

CLAUDE.md

@@ -23,6 +23,10 @@ mix test test/systant_test.exs
 
 # Enter development shell (via Nix)
 nix develop
+
+# Run dashboard (Phoenix LiveView)
+cd dashboard && mix phx.server
+# or use justfile: just dashboard
 ```
 
 ### Production
@@ -41,6 +45,8 @@ This is an Elixir OTP application that serves as a systemd daemon for MQTT-based
 ### Core Components
 - **Systant.Application** (`lib/systant/application.ex`): OTP application supervisor that starts the MQTT client
 - **Systant.MqttClient** (`lib/systant/mqtt_client.ex`): GenServer that handles MQTT connection, publishes stats every 30 seconds, and listens for commands
+- **Dashboard.Application** (`dashboard/lib/dashboard/application.ex`): Phoenix LiveView dashboard application
+- **Dashboard.MqttSubscriber** (`dashboard/lib/dashboard/mqtt_subscriber.ex`): Real-time MQTT subscriber that feeds data to the LiveView dashboard
 - **Configuration**: MQTT settings configurable via environment variables or config files
 
 ### Key Libraries
@@ -73,6 +79,25 @@ The NixOS module supports:
 - Systemd service with security hardening
 - Auto-restart and logging to systemd journal
 
+## Dashboard
+
+The project includes a Phoenix LiveView dashboard (`dashboard/`) that provides real-time monitoring of all systant instances.
+
+### Dashboard Features
+- Real-time host status updates via MQTT subscription
+- LiveView interface showing all connected hosts
+- Automatic reconnection and error handling
+
+### Dashboard MQTT Configuration
+- Subscribes to `systant/+/stats` to receive updates from all hosts
+- Uses hostname-based client ID: `systant-dashboard-${hostname}` to avoid conflicts
+- Connects to `mqtt.home:1883` (same broker as systant instances)
+
+### Important Implementation Notes
+- **Tortoise Handler**: The `handle_message/3` callback must return `{:ok, state}`, not `[]`
+- **Topic Parsing**: Topics may arrive as lists or strings, handle both formats
+- **Client ID Conflicts**: Use unique client IDs to prevent connection instability
+
 ### Future Plans
 - Integration with Home Assistant via custom MQTT integration
 - Expandable command handling for host-specific automation

dashboard/lib/dashboard/mqtt_subscriber.ex

@@ -63,7 +63,7 @@ defmodule Dashboard.MqttSubscriber do
     {:ok, state}
   end
   
-  def handle_message(topic, payload, _state) do
+  def handle_message(topic, payload, state) do
     topic_parts = if is_binary(topic), do: String.split(topic, "/"), else: topic
     case topic_parts do
       ["systant", hostname, "stats"] ->
@@ -83,7 +83,7 @@ defmodule Dashboard.MqttSubscriber do
       _ ->
         :ok
     end
-    []
+    {:ok, state}
   end
 
   @impl true