feat: image fullscreen viewer, public room browser

- Chat: tap any image to open fullscreen InteractiveViewer (pinch/zoom)
- Rooms: public room browser (Find rooms FAB + empty state button)
  searches Matrix room directory via queryPublicRooms, join from results
- Rooms: empty state now shows 'Find rooms' button to onboard new users

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

lib/features/chat/presentation/message_bubble.dart

@@ -1,4 +1,4 @@
-// Version: 1.2.0 | Created: 2026-04-01 | Updated: 2026-04-10
+// Version: 1.3.0 | Created: 2026-04-01 | Updated: 2026-04-27
 // Message bubble widget. Handles text, images, files, redacted, replies.
 
 import 'package:cached_network_image/cached_network_image.dart';
@@ -172,11 +172,15 @@ class _ImageContent extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    if (message.mediaUrl != null) {
+    final url = message.mediaUrl;
-      return ClipRRect(
+    if (url == null) return const Icon(Icons.image_not_supported);
+
+    return GestureDetector(
+      onTap: () => _openFullscreen(context, url, message.body),
+      child: ClipRRect(
         borderRadius: BorderRadius.circular(8),
         child: CachedNetworkImage(
-          imageUrl: message.mediaUrl!,
+          imageUrl: url,
           width: 240,
           fit: BoxFit.cover,
           placeholder: (_, __) => const SizedBox(
@@ -188,9 +192,60 @@ class _ImageContent extends StatelessWidget {
             child: Center(child: Icon(Icons.broken_image)),
           ),
         ),
+      ),
     );
   }
-    return const Icon(Icons.image_not_supported);
+
+  void _openFullscreen(BuildContext context, String url, String? caption) {
+    Navigator.of(context).push(
+      MaterialPageRoute<void>(
+        fullscreenDialog: true,
+        builder: (_) => _ImageViewer(url: url, caption: caption),
+      ),
+    );
+  }
+}
+
+class _ImageViewer extends StatelessWidget {
+  const _ImageViewer({required this.url, this.caption});
+
+  final String url;
+  final String? caption;
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      backgroundColor: Colors.black,
+      appBar: AppBar(
+        backgroundColor: Colors.black,
+        foregroundColor: Colors.white,
+        title: caption != null
+            ? Text(
+                caption!,
+                style: const TextStyle(fontSize: 14),
+                overflow: TextOverflow.ellipsis,
+              )
+            : null,
+      ),
+      body: Center(
+        child: InteractiveViewer(
+          minScale: 0.5,
+          maxScale: 4,
+          child: CachedNetworkImage(
+            imageUrl: url,
+            fit: BoxFit.contain,
+            placeholder: (_, __) => const CircularProgressIndicator(
+              color: Colors.white,
+            ),
+            errorWidget: (_, __, ___) => const Icon(
+              Icons.broken_image,
+              color: Colors.white,
+              size: 64,
+            ),
+          ),
+        ),
+      ),
+    );
   }
 }
 

lib/features/rooms/presentation/public_rooms_dialog.dart

@@ -0,0 +1,225 @@
+// Version: 1.0.0 | Created: 2026-04-27
+// Public room browser — search Matrix room directory and join rooms.
+
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:go_router/go_router.dart';
+import 'package:matrix/matrix_api_lite.dart'
+    show PublicRoomQueryFilter, PublicRoomsChunk;
+import 'package:riverpod_annotation/riverpod_annotation.dart';
+
+import '../../../core/network/matrix_client.dart';
+import '../../../shared/widgets/matrix_avatar.dart';
+
+part 'public_rooms_dialog.g.dart';
+
+@riverpod
+Future<List<PublicRoomsChunk>> publicRooms(
+    Ref ref, String searchTerm) async {
+  final client = ref.watch(matrixClientProvider);
+  final filter = searchTerm.trim().isEmpty
+      ? null
+      : PublicRoomQueryFilter(genericSearchTerm: searchTerm.trim());
+
+  final response = await client.queryPublicRooms(
+    filter: filter,
+    limit: 30,
+  );
+  return response.chunk;
+}
+
+Future<void> showPublicRoomsDialog(BuildContext context) {
+  return showDialog<void>(
+    context: context,
+    builder: (_) => const _PublicRoomsDialog(),
+  );
+}
+
+class _PublicRoomsDialog extends ConsumerStatefulWidget {
+  const _PublicRoomsDialog();
+
+  @override
+  ConsumerState<_PublicRoomsDialog> createState() =>
+      _PublicRoomsDialogState();
+}
+
+class _PublicRoomsDialogState extends ConsumerState<_PublicRoomsDialog> {
+  final _controller = TextEditingController();
+  String _searchTerm = '';
+  Timer? _debounce;
+  String? _joiningRoomId;
+
+  @override
+  void dispose() {
+    _debounce?.cancel();
+    _controller.dispose();
+    super.dispose();
+  }
+
+  void _onSearchChanged(String val) {
+    _debounce?.cancel();
+    _debounce = Timer(const Duration(milliseconds: 450), () {
+      if (mounted) setState(() => _searchTerm = val);
+    });
+  }
+
+  Future<void> _join(PublicRoomsChunk room) async {
+    if (_joiningRoomId != null) return;
+    setState(() => _joiningRoomId = room.roomId);
+
+    try {
+      final client = ref.read(matrixClientProvider);
+      await client.joinRoom(room.canonicalAlias ?? room.roomId);
+      if (!mounted) return;
+      Navigator.of(context).pop();
+      context.push('/rooms/${Uri.encodeComponent(room.roomId)}');
+    } on Exception catch (e) {
+      if (!mounted) return;
+      setState(() => _joiningRoomId = null);
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(content: Text('Could not join room: $e')),
+      );
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final roomsAsync = ref.watch(publicRoomsProvider(_searchTerm));
+
+    return Dialog(
+      insetPadding: const EdgeInsets.symmetric(horizontal: 16, vertical: 32),
+      child: ConstrainedBox(
+        constraints: const BoxConstraints(maxWidth: 520, maxHeight: 600),
+        child: Column(
+          children: [
+            // Header
+            Padding(
+              padding: const EdgeInsets.fromLTRB(16, 16, 4, 0),
+              child: Row(
+                children: [
+                  Text(
+                    'Find rooms',
+                    style: theme.textTheme.titleMedium?.copyWith(
+                      fontWeight: FontWeight.w600,
+                    ),
+                  ),
+                  const Spacer(),
+                  IconButton(
+                    icon: const Icon(Icons.close),
+                    onPressed: () => Navigator.of(context).pop(),
+                  ),
+                ],
+              ),
+            ),
+
+            // Search
+            Padding(
+              padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
+              child: TextField(
+                controller: _controller,
+                autofocus: true,
+                decoration: const InputDecoration(
+                  hintText: 'Search public rooms...',
+                  prefixIcon: Icon(Icons.search),
+                ),
+                onChanged: _onSearchChanged,
+              ),
+            ),
+
+            // Results
+            Flexible(
+              child: roomsAsync.when(
+                loading: () =>
+                    const Center(child: CircularProgressIndicator()),
+                error: (err, _) => Padding(
+                  padding: const EdgeInsets.all(16),
+                  child: Text('Search failed: $err'),
+                ),
+                data: (rooms) {
+                  if (rooms.isEmpty) {
+                    return Padding(
+                      padding: const EdgeInsets.all(24),
+                      child: Text(
+                        _searchTerm.isEmpty
+                            ? 'No public rooms found.'
+                            : 'No rooms match "$_searchTerm".',
+                        textAlign: TextAlign.center,
+                        style: theme.textTheme.bodySmall?.copyWith(
+                          color: theme.colorScheme.onSurface.withAlpha(102),
+                        ),
+                      ),
+                    );
+                  }
+
+                  return ListView.separated(
+                    shrinkWrap: true,
+                    itemCount: rooms.length,
+                    separatorBuilder: (_, __) =>
+                        const Divider(height: 1, indent: 72),
+                    itemBuilder: (context, index) {
+                      final room = rooms[index];
+                      final name = room.name ??
+                          room.canonicalAlias ??
+                          room.roomId;
+                      final isJoining = _joiningRoomId == room.roomId;
+
+                      return ListTile(
+                        leading: MatrixAvatar(
+                          name: name,
+                          avatarUrl: room.avatarUrl?.toString(),
+                          radius: 20,
+                        ),
+                        title: Text(
+                          name,
+                          overflow: TextOverflow.ellipsis,
+                        ),
+                        subtitle: Column(
+                          crossAxisAlignment: CrossAxisAlignment.start,
+                          mainAxisSize: MainAxisSize.min,
+                          children: [
+                            if (room.topic != null)
+                              Text(
+                                room.topic!,
+                                maxLines: 1,
+                                overflow: TextOverflow.ellipsis,
+                                style: theme.textTheme.bodySmall,
+                              ),
+                            Text(
+                              '${room.numJoinedMembers} member'
+                              '${room.numJoinedMembers == 1 ? '' : 's'}',
+                              style: theme.textTheme.bodySmall?.copyWith(
+                                color: theme.colorScheme.onSurface
+                                    .withAlpha(120),
+                              ),
+                            ),
+                          ],
+                        ),
+                        isThreeLine: room.topic != null,
+                        trailing: isJoining
+                            ? const SizedBox(
+                                width: 20,
+                                height: 20,
+                                child: CircularProgressIndicator(
+                                    strokeWidth: 2),
+                              )
+                            : OutlinedButton(
+                                onPressed: _joiningRoomId != null
+                                    ? null
+                                    : () => _join(room),
+                                child: const Text('Join'),
+                              ),
+                      );
+                    },
+                  );
+                },
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}

lib/features/rooms/presentation/rooms_screen.dart

@@ -1,4 +1,4 @@
-// Version: 1.4.0 | Created: 2026-04-01 | Updated: 2026-04-27
+// Version: 1.5.0 | Created: 2026-04-01 | Updated: 2026-04-27
 // Main rooms list screen with bottom navigation.
 
 import 'package:flutter/material.dart';
@@ -9,6 +9,7 @@ import '../../help/presentation/help_tab.dart';
 import '../../jitsi/presentation/conference_tab.dart';
 import '../../profile/presentation/profile_screen.dart';
 import '../../spaces/presentation/spaces_screen.dart';
+import 'public_rooms_dialog.dart';
 import 'room_tile.dart';
 import 'rooms_controller.dart';
 import 'user_search_dialog.dart';
@@ -113,6 +114,13 @@ class _RoomsScreenState extends ConsumerState<RoomsScreen> {
             )
           : null,
       body: _buildBody(),
+      floatingActionButton: _selectedIndex == 0 && !_searchActive
+          ? FloatingActionButton(
+              onPressed: () => showPublicRoomsDialog(context),
+              tooltip: 'Find rooms',
+              child: const Icon(Icons.explore_outlined),
+            )
+          : null,
       bottomNavigationBar: NavigationBar(
         selectedIndex: _selectedIndex,
         onDestinationSelected: (index) =>
@@ -233,11 +241,19 @@ class _EmptyRoomsState extends StatelessWidget {
             ),
             const SizedBox(height: 8),
             Text(
-              'Rooms you join will appear here.',
+              'Use the pencil icon above to message someone, or find '
+              'a public room to join.',
+              textAlign: TextAlign.center,
               style: theme.textTheme.bodySmall?.copyWith(
                 color: theme.colorScheme.onSurface.withAlpha(102),
               ),
             ),
+            const SizedBox(height: 20),
+            OutlinedButton.icon(
+              onPressed: () => showPublicRoomsDialog(context),
+              icon: const Icon(Icons.explore_outlined),
+              label: const Text('Find rooms'),
+            ),
           ],
         ),
       ),

pubspec.yaml

@@ -1,7 +1,7 @@
 name: m8chat_app
 description: "M8Chat — Matrix chat client for Android, iOS, and Web."
 publish_to: 'none'
-version: 1.3.1+5
+version: 1.4.0+6
 
 environment:
   sdk: '>=3.11.0 <4.0.0'