feat(android): 4-state connection banner with unstable + back-online flash

Banner VM collects NetworkStatusController.state directly (drops the redundant
WhileSubscribed re-wrap). Adds a mild 'Reconnecting…' treatment for the
non-gating Unstable state and a transient 'Back online' confirmation on
down→Healthy recovery (try/finally guards against a stuck flash).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

android/app/src/main/java/com/fabledsword/minstrel/connectivity/ui/ConnectionErrorBanner.kt

@@ -14,84 +14,121 @@ import androidx.compose.material3.Icon
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.unit.dp
 import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.SavedStateHandle
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
-import androidx.lifecycle.viewModelScope
 import com.composables.icons.lucide.CloudOff
 import com.composables.icons.lucide.Lucide
 import com.fabledsword.minstrel.connectivity.NetworkStatusController
 import com.fabledsword.minstrel.connectivity.ServerHealth
 import dagger.hilt.android.lifecycle.HiltViewModel
-import kotlinx.coroutines.flow.SharingStarted
+import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.StateFlow
-import kotlinx.coroutines.flow.stateIn
 import javax.inject.Inject
 
-private const val HEALTH_SHARE_STOP_TIMEOUT_MS = 5_000L
+private const val BACK_ONLINE_FLASH_MS = 2_000L
 
 /**
- * Lifts [NetworkStatusController]'s tri-state into a StateFlow for the banner
- * composable. Keeps the banner pure-presentation.
+ * Exposes [NetworkStatusController]'s tri-state directly to the banner. No
+ * re-wrapping StateFlow — the controller's is already app-scoped and warm.
  */
 @HiltViewModel
 class ConnectivityBannerViewModel @Inject constructor(
-    health: NetworkStatusController,
+    networkStatus: NetworkStatusController,
     @Suppress("UnusedPrivateProperty") savedStateHandle: SavedStateHandle,
 ) : ViewModel() {
-    val health: StateFlow<ServerHealth> = health.state.stateIn(
-        scope = viewModelScope,
-        started = SharingStarted.WhileSubscribed(HEALTH_SHARE_STOP_TIMEOUT_MS),
-        initialValue = ServerHealth.Healthy,
-    )
+    val health: StateFlow<ServerHealth> = networkStatus.state
 }
 
 /**
- * Banner shown at the top of the shell when the user can't reach the server.
- * Tri-state so we tell the user *why*: no device network vs server-down.
- * Copy choices match the Flutter analogues. Auto-hides via slide+fade when
- * health returns to [ServerHealth.Healthy].
+ * Shell banner. Tells the user *why* they're degraded — no link vs server-down
+ * — plus a non-alarming "Reconnecting…" for the transient [ServerHealth.Unstable]
+ * window, and a brief "Back online" confirmation when health recovers so
+ * recovery is unmistakable. Sentence case, understated voice (design system).
  */
 @Composable
 fun ConnectionErrorBanner(
     viewModel: ConnectivityBannerViewModel = hiltViewModel(),
 ) {
     val health by viewModel.health.collectAsStateWithLifecycle()
+    var showBackOnline by remember { mutableStateOf(false) }
+    var wasDown by remember { mutableStateOf(false) }
+
+    LaunchedEffect(health) {
+        val down = health == ServerHealth.Offline || health == ServerHealth.ServerDown
+        if (health == ServerHealth.Healthy && wasDown) {
+            // try/finally so a mid-delay cancellation (health flips again) can't
+            // orphan the flag and leave "Back online" stuck on screen.
+            try {
+                showBackOnline = true
+                delay(BACK_ONLINE_FLASH_MS)
+            } finally {
+                showBackOnline = false
+            }
+        }
+        wasDown = down
+    }
+
     AnimatedVisibility(
-        visible = health != ServerHealth.Healthy,
+        visible = health != ServerHealth.Healthy || showBackOnline,
         enter = expandVertically() + fadeIn(),
         exit = shrinkVertically() + fadeOut(),
     ) {
-        Row(
-            modifier = Modifier
-                .fillMaxWidth()
-                .background(MaterialTheme.colorScheme.errorContainer)
-                .padding(horizontal = 16.dp, vertical = 10.dp),
-            verticalAlignment = Alignment.CenterVertically,
-            horizontalArrangement = Arrangement.spacedBy(12.dp),
-        ) {
-            Icon(
-                imageVector = Lucide.CloudOff,
-                contentDescription = null,
-                tint = MaterialTheme.colorScheme.onErrorContainer,
-            )
-            Text(
-                text = when (health) {
-                    ServerHealth.Offline ->
-                        "No connection — check Wi-Fi or mobile data."
-                    ServerHealth.ServerDown ->
-                        "Server unreachable — your cached content is still available."
-                    ServerHealth.Unstable -> "Reconnecting…"
-                    ServerHealth.Healthy -> ""
-                },
-                style = MaterialTheme.typography.bodyMedium,
-                color = MaterialTheme.colorScheme.onErrorContainer,
-            )
-        }
+        BannerContent(health = health, backOnline = showBackOnline)
     }
 }
+
+@Composable
+private fun BannerContent(health: ServerHealth, backOnline: Boolean) {
+    val scheme = MaterialTheme.colorScheme
+    val background: Color
+    val foreground: Color
+    when {
+        backOnline -> {
+            background = scheme.secondaryContainer
+            foreground = scheme.onSecondaryContainer
+        }
+        health == ServerHealth.Unstable -> {
+            background = scheme.surfaceVariant
+            foreground = scheme.onSurfaceVariant
+        }
+        else -> {
+            background = scheme.errorContainer
+            foreground = scheme.onErrorContainer
+        }
+    }
+    Row(
+        modifier = Modifier
+            .fillMaxWidth()
+            .background(background)
+            .padding(horizontal = 16.dp, vertical = 10.dp),
+        verticalAlignment = Alignment.CenterVertically,
+        horizontalArrangement = Arrangement.spacedBy(12.dp),
+    ) {
+        Icon(imageVector = Lucide.CloudOff, contentDescription = null, tint = foreground)
+        Text(
+            text = bannerText(health, backOnline),
+            style = MaterialTheme.typography.bodyMedium,
+            color = foreground,
+        )
+    }
+}
+
+private fun bannerText(health: ServerHealth, backOnline: Boolean): String = when {
+    backOnline -> "Back online."
+    health == ServerHealth.Offline -> "No connection — check Wi-Fi or mobile data."
+    health == ServerHealth.ServerDown ->
+        "Server unreachable — your cached content is still available."
+    health == ServerHealth.Unstable -> "Reconnecting…"
+    else -> ""
+}