feat: notify user when claude.ai session expires (tap to re-auth)

Detection already cleared the session after 3x 401/403 but did so silently —
the widget would just go stale. Now fires a one-time HIGH-priority notification
on its own 'Sign-in alerts' channel that opens LoginActivity for re-paste.

app/src/main/java/me/khodak/claudeusage/Notifier.kt

@@ -23,8 +23,42 @@ import me.khodak.claudeusage.data.UsageData
 object Notifier {
 
     private const val CHANNEL_ID = "usage_alerts"
+    private const val AUTH_CHANNEL_ID = "session_alerts"
+    private const val AUTH_NOTIF_ID = 3000
     private val LEVELS = intArrayOf(90, 100)
 
+    /**
+     * Fired once when the saved claude.ai session is cleared after repeated 401/403s — without
+     * this the widget would just silently go stale and the user would have to notice the dead
+     * data themselves. Tapping opens LoginActivity straight to the cookie re-paste flow. Posts on
+     * its own channel so it can be muted independently of usage alerts, and is not gated on the
+     * usage-alert toggle: a dead widget is a functional failure the user needs to know about.
+     */
+    fun notifySessionExpired(context: Context) {
+        val mgr = NotificationManagerCompat.from(context)
+        if (!mgr.areNotificationsEnabled()) return
+        ensureAuthChannel(context)
+        val intent = Intent(context, LoginActivity::class.java)
+            .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TOP)
+        val pi = PendingIntent.getActivity(
+            context, 1, intent,
+            PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE
+        )
+        val notif = NotificationCompat.Builder(context, AUTH_CHANNEL_ID)
+            .setSmallIcon(R.drawable.ic_claude_burst)
+            .setContentTitle("Claude sign-in expired")
+            .setContentText("Tap to sign in again — the widget can't update until you do.")
+            .setPriority(NotificationCompat.PRIORITY_HIGH)
+            .setAutoCancel(true)
+            .setContentIntent(pi)
+            .build()
+        try {
+            mgr.notify(AUTH_NOTIF_ID, notif)
+        } catch (_: SecurityException) {
+            // Notifications revoked between the check and post — nothing to do.
+        }
+    }
+
     fun checkAndNotify(context: Context, prefs: PreferencesManager, data: UsageData) {
         if (!prefs.isNotifyEnabled()) return
         val mgr = NotificationManagerCompat.from(context)
@@ -94,6 +128,17 @@ object Notifier {
     private fun notifId(metric: String, levelIndex: Int) =
         2000 + (if (metric == "weekly") 10 else 0) + levelIndex
 
+    private fun ensureAuthChannel(context: Context) {
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) return
+        val mgr = context.getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
+        if (mgr.getNotificationChannel(AUTH_CHANNEL_ID) != null) return
+        mgr.createNotificationChannel(
+            NotificationChannel(
+                AUTH_CHANNEL_ID, "Sign-in alerts", NotificationManager.IMPORTANCE_HIGH
+            ).apply { description = "Tells you when your claude.ai session expires and needs re-auth" }
+        )
+    }
+
     private fun ensureChannel(context: Context) {
         if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) return
         val mgr = context.getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager

app/src/main/java/me/khodak/claudeusage/UsageUpdateWorker.kt

@@ -31,10 +31,16 @@ class UsageUpdateWorker(
             val animJob = launch { rotateRefreshIcon() }
             try {
                 val data = UsageRepository(prefs).fetchUsage()
+                // We passed the isLoggedIn() guard above, so if the session is gone now the
+                // cookie just expired this cycle — tell the user once (next cycle returns early).
+                if (!prefs.isLoggedIn()) {
+                    Notifier.notifySessionExpired(context)
+                } else {
                     // Preserve last-good data so a failed/partial fetch never blanks the widget.
                     prefs.saveUsageData(data.mergedWith(prefs.getUsageData()))
                     prefs.recordHistory(data)       // history records only fresh readings
                     Notifier.checkAndNotify(context, prefs, data)
+                }
             } catch (_: Exception) {}
             animJob.cancel()
             animJob.join()