feat(ws): consume gateway change events (issue #784) (#837)

* feat(ws): consume gateway change events (cron/sessions/platforms/pairing) for targeted refresh (issue #784)

* test(chat): complete catch-all request stub — kill frozen-collector capture race (slash-focus flake, 4645a2b CI)

---------

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/main/java/com/m57/hermescontrol/ui/common/ViewModelExt.kt

@@ -3,7 +3,9 @@ package com.m57.hermescontrol.ui.common
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import com.m57.hermescontrol.data.remote.NetworkResult
+import com.m57.hermescontrol.data.ws.ChangeEventHub
 import kotlinx.coroutines.Job
+import kotlinx.coroutines.flow.filter
 import kotlinx.coroutines.launch
 
 interface ToastHost {
@@ -31,3 +33,41 @@ inline fun <T> ViewModel.safeLaunchLoad(
         }
     }
 }
+
+/**
+ * Collect a gateway change event ([com.m57.hermescontrol.data.ws.ChangeEvents])
+ * from [ChangeEventHub] and run a **silent** refresh: no loading spinner, no
+ * error surface — stale data stays in place on failure. At most one request
+ * runs at a time; events arriving mid-flight are skipped, so a
+ * `sessions.changed` burst during a long streaming turn (the gateway floors
+ * those at 2s) cannot pile up requests.
+ *
+ * Call from `init`. Backends without `change_events` never broadcast, and in
+ * unit tests the hub is never fed (HermesWsClient is mocked or uninitialized),
+ * so this is a no-op there — exactly the "slow backstop" contract of issue
+ * #784.
+ */
+inline fun <T> ViewModel.refreshOnChange(
+    eventType: String,
+    crossinline apiCall: suspend () -> NetworkResult<T>,
+    crossinline onSuccess: (T) -> Unit,
+): Job {
+    var refreshInFlight = false
+    return viewModelScope.launch {
+        ChangeEventHub.events
+            .filter { it.type == eventType }
+            .collect { _ ->
+                if (refreshInFlight) return@collect
+                refreshInFlight = true
+                try {
+                    // No Dispatchers.IO hop — see safeLaunchLoad.
+                    val result = apiCall()
+                    if (result is NetworkResult.Success) {
+                        onSuccess(result.data)
+                    }
+                } finally {
+                    refreshInFlight = false
+                }
+            }
+    }
+}