fix channel shutnown exception

CHANGELOG.txt

@@ -1,3 +1,13 @@
+2026-02-13
+fix: prevent agent channel graceful shutdowns from being logged as exceptions
+  - Changed Phoenix Channel stop reasons to use {:shutdown, reason} tuple instead
+    of bare atoms to signal graceful termination
+  - Updated heartbeat_timeout, token_disabled, and restart_requested handlers
+  - Prevents error tracking systems from incorrectly reporting normal agent
+    disconnections as ErlangError exceptions
+  - These events are expected operational occurrences (timeouts, admin actions)
+  - File: lib/towerops_web/channels/agent_channel.ex
+
 2026-02-12
 feat: complete migration from DevicePollerWorker to CheckExecutorWorker
   - Removed all DevicePollerWorker scheduling from device lifecycle

lib/towerops_web/channels/agent_channel.ex

@@ -193,7 +193,7 @@ defmodule ToweropsWeb.AgentChannel do
         agent_token_id: socket.assigns.agent_token_id
       )
 
-      {:stop, :heartbeat_timeout, socket}
+      {:stop, {:shutdown, :heartbeat_timeout}, socket}
     else
       Process.send_after(self(), :check_heartbeat, @heartbeat_check_interval_ms)
       {:noreply, socket}
@@ -206,7 +206,7 @@ defmodule ToweropsWeb.AgentChannel do
       agent_token_id: socket.assigns.agent_token_id
     )
 
-    {:stop, :token_disabled, socket}
+    {:stop, {:shutdown, :token_disabled}, socket}
   end
 
   # Handle restart request — push restart event to agent, then stop channel
@@ -216,7 +216,7 @@ defmodule ToweropsWeb.AgentChannel do
     )
 
     push(socket, "restart", %{})
-    {:stop, :restart_requested, socket}
+    {:stop, {:shutdown, :restart_requested}, socket}
   end
 
   # Handle update request — push update event with download URL and checksum to agent