feat: background update download, snackbar prompt, chat image rendering

Update provider: auto-downloads APK in background after finding a newer
version, prompts via snackbar only when ready, cleans up old APKs on
startup. Replaces modal dialog with dismissible snackbar.

Chat bubble: resolve relative image URLs (/api/images/{id}) against
server base URL with auth cookies so search_images results render on
the phone app.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/providers/update_provider.dart

@@ -1,3 +1,5 @@
+import 'dart:io';
+
 import 'package:dio/dio.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:open_file/open_file.dart';
@@ -5,7 +7,14 @@ import 'package:package_info_plus/package_info_plus.dart';
 import 'package:path_provider/path_provider.dart';
 import 'package:permission_handler/permission_handler.dart';
 
-enum UpdateStatus { idle, checking, available, downloading, upToDate, error }
+enum UpdateStatus {
+  idle,
+  checking,
+  downloading,
+  readyToInstall,
+  upToDate,
+  error,
+}
 
 class UpdateState {
   final UpdateStatus status;
@@ -14,6 +23,7 @@ class UpdateState {
   final String? downloadUrl;
   final double downloadProgress;
   final String? errorMessage;
+  final String? apkPath;
 
   const UpdateState({
     this.status = UpdateStatus.idle,
@@ -22,6 +32,7 @@ class UpdateState {
     this.downloadUrl,
     this.downloadProgress = 0.0,
     this.errorMessage,
+    this.apkPath,
   });
 
   UpdateState copyWith({
@@ -31,6 +42,7 @@ class UpdateState {
     String? downloadUrl,
     double? downloadProgress,
     String? errorMessage,
+    String? apkPath,
   }) =>
       UpdateState(
         status: status ?? this.status,
@@ -39,6 +51,7 @@ class UpdateState {
         downloadUrl: downloadUrl ?? this.downloadUrl,
         downloadProgress: downloadProgress ?? this.downloadProgress,
         errorMessage: errorMessage ?? this.errorMessage,
+        apkPath: apkPath ?? this.apkPath,
       );
 }
 
@@ -46,20 +59,15 @@ class UpdateNotifier extends Notifier<UpdateState> {
   @override
   UpdateState build() => const UpdateState();
 
-  /// [repoUrl] is the Forgejo repo page URL, e.g.
-  /// "https://git.example.com/user/fabled_app"
   Future<void> check(String repoUrl) async {
     state = state.copyWith(status: UpdateStatus.checking);
     try {
       final packageInfo = await PackageInfo.fromPlatform();
-      // Combine versionName + buildNumber to match the YY.MM.DD.N tag format.
       final currentVersion =
           '${packageInfo.version}.${packageInfo.buildNumber}';
 
-      // Parse repo URL → Forgejo API endpoint
       final uri = Uri.parse(repoUrl);
-      final parts =
-          uri.pathSegments.where((s) => s.isNotEmpty).toList();
+      final parts = uri.pathSegments.where((s) => s.isNotEmpty).toList();
       if (parts.length < 2) throw 'Invalid repository URL (need /owner/repo)';
       final apiUrl =
           '${uri.scheme}://${uri.authority}/api/v1/repos/${parts[0]}/${parts[1]}/releases/latest';
@@ -70,20 +78,20 @@ class UpdateNotifier extends Notifier<UpdateState> {
           tagName.startsWith('v') ? tagName.substring(1) : tagName;
 
       if (_isNewer(latestVersion, currentVersion)) {
-        final assets =
-            (response.data['assets'] as List<dynamic>? ?? [])
-                .cast<Map<String, dynamic>>();
+        final assets = (response.data['assets'] as List<dynamic>? ?? [])
+            .cast<Map<String, dynamic>>();
         final apk = assets.firstWhere(
           (a) => (a['name'] as String? ?? '').endsWith('.apk'),
           orElse: () => {},
         );
         if (apk.isNotEmpty) {
+          final downloadUrl = apk['browser_download_url'] as String?;
           state = state.copyWith(
-            status: UpdateStatus.available,
             currentVersion: currentVersion,
             latestVersion: latestVersion,
-            downloadUrl: apk['browser_download_url'] as String?,
+            downloadUrl: downloadUrl,
           );
+          await _downloadInBackground();
           return;
         }
       }
@@ -101,11 +109,52 @@ class UpdateNotifier extends Notifier<UpdateState> {
     }
   }
 
-  Future<void> downloadAndInstall() async {
+  Future<void> _downloadInBackground() async {
     if (state.downloadUrl == null) return;
+    state = state.copyWith(status: UpdateStatus.downloading, downloadProgress: 0);
+
+    try {
+      final dir = await _apkDir();
+      await _cleanupApks(dir);
+
+      final path = '${dir.path}/fabled_${state.latestVersion}.apk';
+
+      await Dio().download(
+        state.downloadUrl!,
+        path,
+        onReceiveProgress: (received, total) {
+          if (total > 0) {
+            state = state.copyWith(downloadProgress: received / total);
+          }
+        },
+      );
+
+      final file = File(path);
+      if (!await file.exists() || await file.length() == 0) {
+        state = state.copyWith(
+          status: UpdateStatus.error,
+          errorMessage: 'Download failed — file is empty',
+        );
+        return;
+      }
+
+      state = state.copyWith(
+        status: UpdateStatus.readyToInstall,
+        apkPath: path,
+        downloadProgress: 1.0,
+      );
+    } catch (e) {
+      state = state.copyWith(
+        status: UpdateStatus.error,
+        errorMessage: e.toString(),
+      );
+    }
+  }
+
+  Future<void> install() async {
+    final path = state.apkPath;
+    if (path == null) return;
 
-    // Android 8+ requires explicit per-app "Install unknown apps" approval
-    // beyond the manifest declaration. Check and redirect to Settings if needed.
     final installPermission = await Permission.requestInstallPackages.status;
     if (!installPermission.isGranted) {
       final result = await Permission.requestInstallPackages.request();
@@ -119,30 +168,13 @@ class UpdateNotifier extends Notifier<UpdateState> {
       }
     }
 
-    state = state.copyWith(status: UpdateStatus.downloading, downloadProgress: 0);
-
     try {
-      final dir = await getExternalStorageDirectory() ??
-          await getTemporaryDirectory();
-      final path = '${dir.path}/fabled_update.apk';
-
-      await Dio().download(
-        state.downloadUrl!,
-        path,
-        onReceiveProgress: (received, total) {
-          if (total > 0) {
-            state = state.copyWith(downloadProgress: received / total);
-          }
-        },
-      );
-
       final result = await OpenFile.open(
         path,
         type: 'application/vnd.android.package-archive',
       );
 
       if (result.type == ResultType.done) {
-        // Installer launched — reset to idle so the dialog closes naturally.
         state = const UpdateState();
       } else {
         state = state.copyWith(
@@ -158,8 +190,30 @@ class UpdateNotifier extends Notifier<UpdateState> {
     }
   }
 
+  /// Remove any previously cached APKs.
+  Future<void> cleanup() async {
+    final dir = await _apkDir();
+    await _cleanupApks(dir);
+  }
+
   void dismiss() => state = const UpdateState();
 
+  Future<Directory> _apkDir() async {
+    return await getExternalStorageDirectory() ??
+        await getTemporaryDirectory();
+  }
+
+  Future<void> _cleanupApks(Directory dir) async {
+    try {
+      final entries = dir.listSync();
+      for (final entry in entries) {
+        if (entry is File && entry.path.endsWith('.apk')) {
+          await entry.delete();
+        }
+      }
+    } catch (_) {}
+  }
+
   bool _isNewer(String latest, String current) {
     try {
       final l = latest.split('.').map(int.parse).toList();