feat(mobile): allow selecting and copying message text

mobile/lib/features/channels/channel_detail_page/message_bubble.dart

@@ -80,6 +80,8 @@ class _MessageBubble extends HookConsumerWidget {
       agentMentionPubkeys: agentMentionPubkeys,
     );
 
+    final selecting = ref.watch(messageTextSelectionIdProvider) == message.id;
+
     void openMessageActions(MessageLongPressDetails details) {
       showMessageActions(
         context: context,
@@ -97,6 +99,9 @@ class _MessageBubble extends HookConsumerWidget {
         onPopoverDismissed: () => details.setSourceHidden(false),
         composerFocusNode: composerFocusNode,
         restoreComposerFocus: restoreComposerFocus,
+        onSelectText: () {
+          ref.read(messageTextSelectionIdProvider.notifier).state = message.id;
+        },
       );
     }
 
@@ -111,13 +116,14 @@ class _MessageBubble extends HookConsumerWidget {
         clipBehavior: Clip.none,
         child: MessageLongPressInkWell(
           key: ValueKey('message-row-${message.id}'),
+          enabled: !selecting,
           onLongPressDetails: openMessageActions,
           borderRadius: BorderRadius.circular(Radii.md),
           highlightColor: context.colors.primary.withValues(alpha: 0.1),
           snapshotKey: messageSnapshotKey,
           // Tap opens the thread; long-press still opens the action sheet.
           // MessageContent handles mention, channel-link, and media taps.
-          onTap: allMessages == null
+          onTap: selecting || allMessages == null
               ? null
               : () => Navigator.of(context).push(
                   MaterialPageRoute<void>(
@@ -213,11 +219,21 @@ class _MessageBubble extends HookConsumerWidget {
                                               ),
                                         ),
                                       ],
+                                      if (selecting) ...[
+                                        const SizedBox(width: Grid.half),
+                                        const MessageTextSelectionDoneButton(),
+                                      ],
                                     ],
                                   ),
+                                )
+                              else if (selecting)
+                                const Align(
+                                  alignment: Alignment.centerRight,
+                                  child: MessageTextSelectionDoneButton(),
                                 ),
                               MessageContent(
                                 content: message.content,
+                                selectable: selecting,
                                 mentionNames: resolvedMentionNames,
                                 agentMentionPubkeys: agentMentionPubkeys,
                                 channelNames: channelNames,

mobile/lib/features/channels/message_actions.dart

@@ -55,6 +55,9 @@ final _messageActionBackdropFilter = ImageFilter.blur(
   sigmaY: _messageActionBackdropBlurSigma,
 );
 
+/// The message or forum post currently in substring-selection mode, if any.
+final messageTextSelectionIdProvider = StateProvider<String?>((ref) => null);
+
 /// Presents the actions for [message] as an anchored popover when both
 /// [anchorRect] and [captureAnchorSnapshot] are supplied, otherwise as a sheet.
 ///
@@ -87,6 +90,7 @@ void showMessageActions({
   VoidCallback? restoreComposerFocus,
   bool isArchived = false,
   EdgeInsets popoverSpotlightPadding = const EdgeInsets.all(Grid.xxs),
+  VoidCallback? onSelectText,
 }) {
   final hasReactionOnlyActions = message.isSystem && !canManageMessage;
   if (anchorRect != null && hasReactionOnlyActions) {
@@ -116,6 +120,7 @@ void showMessageActions({
     onPopoverDismissed: onPopoverDismissed,
     composerFocusNode: composerFocusNode,
     restoreComposerFocus: restoreComposerFocus,
+    onSelectText: onSelectText,
   )) {
     return;
   }
@@ -178,6 +183,15 @@ void showMessageActions({
                         Clipboard.setData(data);
                       },
                     ),
+                    ListTile(
+                      contentPadding: EdgeInsets.zero,
+                      leading: const Icon(LucideIcons.textCursorInput),
+                      title: const Text('Select text'),
+                      onTap: () {
+                        Navigator.of(sheetContext).pop();
+                        onSelectText?.call();
+                      },
+                    ),
                   ],
                   if (canManageMessage) ...[
                     if (!message.isSystem) const SheetDivider(),
@@ -460,6 +474,34 @@ String messageLinkFor({
   );
 }
 
+/// Exits [messageTextSelectionIdProvider] for the message currently selecting.
+class MessageTextSelectionDoneButton extends ConsumerWidget {
+  const MessageTextSelectionDoneButton({super.key});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    return TextButton(
+      key: const ValueKey('message-select-text-done'),
+      onPressed: () {
+        ref.read(messageTextSelectionIdProvider.notifier).state = null;
+      },
+      style: TextButton.styleFrom(
+        visualDensity: VisualDensity.compact,
+        padding: const EdgeInsets.symmetric(horizontal: Grid.xxs),
+        minimumSize: Size.zero,
+        tapTargetSize: MaterialTapTargetSize.shrinkWrap,
+      ),
+      child: Text(
+        'Done',
+        style: context.textTheme.labelMedium?.copyWith(
+          color: context.colors.primary,
+          fontWeight: FontWeight.w600,
+        ),
+      ),
+    );
+  }
+}
+
 class _MarkReadUnreadTile extends ConsumerWidget {
   final TimelineMessage message;
   final String channelId;

mobile/lib/features/channels/message_actions/message_action_popover.dart

@@ -56,6 +56,7 @@ bool _tryShowMessageActionsPopover({
   required VoidCallback? onPopoverDismissed,
   required FocusNode? composerFocusNode,
   required VoidCallback? restoreComposerFocus,
+  required VoidCallback? onSelectText,
 }) {
   if (anchorRect == null || captureAnchorSnapshot == null) return false;
   final shouldRestoreComposerFocus = composerFocusNode?.hasFocus ?? false;
@@ -77,6 +78,7 @@ bool _tryShowMessageActionsPopover({
       composerFocusNode: composerFocusNode,
       restoreComposerFocus: restoreComposerFocus,
       shouldRestoreComposerFocus: shouldRestoreComposerFocus,
+      onSelectText: onSelectText,
     ).then((shown) {
       if (shown || !context.mounted) return;
       showMessageActions(
@@ -89,6 +91,7 @@ bool _tryShowMessageActionsPopover({
         currentPubkey: currentPubkey,
         isMember: isMember,
         isArchived: isArchived,
+        onSelectText: onSelectText,
       );
     }),
   );
@@ -112,6 +115,7 @@ Future<bool> _showMessageActionsPopover({
   required FocusNode? composerFocusNode,
   required VoidCallback? restoreComposerFocus,
   required bool shouldRestoreComposerFocus,
+  required VoidCallback? onSelectText,
 }) async {
   if (_messageActionPresentationInFlight) return true;
   _messageActionPresentationInFlight = true;
@@ -127,6 +131,7 @@ Future<bool> _showMessageActionsPopover({
       currentPubkey: currentPubkey,
       isMember: isMember,
       isArchived: isArchived,
+      onSelectText: onSelectText,
     );
     if (actions.isEmpty) return false;
     final nativeActionSurfaceSupport = _supportsIosNativeMessageActionSurface();
@@ -229,6 +234,7 @@ List<_PopoverMessageAction> _buildPopoverMessageActions({
   required String? currentPubkey,
   required bool isMember,
   required bool isArchived,
+  required VoidCallback? onSelectText,
 }) {
   final actions = <_PopoverMessageAction>[];
   final messages = allMessages;
@@ -363,6 +369,17 @@ List<_PopoverMessageAction> _buildPopoverMessageActions({
             Clipboard.setData(ClipboardData(text: message.content)),
       ),
     );
+    if (onSelectText != null) {
+      actions.add(
+        _PopoverMessageAction(
+          id: 'selectText',
+          title: 'Select text',
+          icon: LucideIcons.textCursorInput,
+          group: _PopoverMessageActionGroup.utility,
+          onSelected: onSelectText,
+        ),
+      );
+    }
   }
 
   if (canManageMessage) {
@@ -409,11 +426,12 @@ List<_PopoverMessageAction> _buildPopoverMessageActions({
     'markUnread': 1,
     'edit': 2,
     'copyText': 3,
-    'copyLink': 4,
-    'remind': 5,
-    'followThread': 6,
-    'unfollowThread': 6,
-    'delete': 7,
+    'selectText': 4,
+    'copyLink': 5,
+    'remind': 6,
+    'followThread': 7,
+    'unfollowThread': 7,
+    'delete': 8,
   };
   actions.sort(
     (left, right) => actionOrder[left.id]!.compareTo(actionOrder[right.id]!),
@@ -446,6 +464,7 @@ class _PopoverMessageAction {
     'markUnread' => 'envelope.badge',
     'edit' => 'pencil',
     'copyText' => 'doc.on.doc',
+    'selectText' => 'text.cursor',
     'copyLink' => 'link',
     'remind' => 'clock',
     'followThread' => 'bell',

mobile/lib/features/channels/message_content.dart

@@ -133,6 +133,10 @@ class MessageContent extends HookConsumerWidget {
   /// gutter while keeping its first image and count aligned with the body.
   final double mediaCarouselTrailingOverflow;
 
+  /// When true, wrap the markdown body in a [SelectionArea] so the user can
+  /// highlight a substring and use the platform copy menu.
+  final bool selectable;
+
   const MessageContent({
     super.key,
     required this.content,
@@ -150,6 +154,7 @@ class MessageContent extends HookConsumerWidget {
     this.scaleEmojiOnly = false,
     this.mediaCarouselLeadingOverflow = 0,
     this.mediaCarouselTrailingOverflow = 0,
+    this.selectable = false,
   });
 
   @override
@@ -304,13 +309,19 @@ class MessageContent extends HookConsumerWidget {
         ],
       ),
     );
-    if (trailingGallery == null) return markdown;
+    final body = selectable
+        ? SelectionArea(
+            key: const ValueKey('message-content-selection-area'),
+            child: markdown,
+          )
+        : markdown;
+    if (trailingGallery == null) return body;
 
     return Column(
       crossAxisAlignment: CrossAxisAlignment.start,
       mainAxisSize: MainAxisSize.min,
       children: [
-        if (trailingGallery.content.trim().isNotEmpty) markdown,
+        if (trailingGallery.content.trim().isNotEmpty) body,
         _MessageImageCarousel(
           key: ValueKey(
             trailingGallery.items.map((item) => item.url).join('\u0000'),

mobile/lib/features/channels/message_long_press_region.dart

@@ -60,6 +60,10 @@ class MessageLongPressInkWell extends StatelessWidget {
   final GlobalKey? snapshotKey;
   final Widget child;
 
+  /// When false, the long-press interceptor is omitted so platform text
+  /// selection can take the pointer.
+  final bool enabled;
+
   const MessageLongPressInkWell({
     super.key,
     this.onTap,
@@ -68,11 +72,19 @@ class MessageLongPressInkWell extends StatelessWidget {
     this.borderRadius,
     this.highlightColor,
     this.snapshotKey,
+    this.enabled = true,
     required this.child,
   }) : assert(onLongPress != null || onLongPressDetails != null);
 
   @override
   Widget build(BuildContext context) {
+    final inkWell = InkWell(
+      onTap: enabled ? onTap : null,
+      borderRadius: borderRadius,
+      highlightColor: highlightColor,
+      child: child,
+    );
+    if (!enabled) return inkWell;
     return _MessageLongPressRegion(
       onTap: onTap,
       onLongPress: onLongPress,

mobile/lib/features/channels/thread_detail_page/thread_message.dart

@@ -75,6 +75,8 @@ class _ThreadMessage extends HookConsumerWidget {
       agentMentionPubkeys: agentMentionPubkeys,
     );
 
+    final selecting = ref.watch(messageTextSelectionIdProvider) == message.id;
+
     void openMessageActions(MessageLongPressDetails details) {
       showMessageActions(
         context: context,
@@ -92,6 +94,9 @@ class _ThreadMessage extends HookConsumerWidget {
         onPopoverDismissed: () => details.setSourceHidden(false),
         composerFocusNode: composerFocusNode,
         restoreComposerFocus: restoreComposerFocus,
+        onSelectText: () {
+          ref.read(messageTextSelectionIdProvider.notifier).state = message.id;
+        },
       );
     }
 
@@ -137,6 +142,7 @@ class _ThreadMessage extends HookConsumerWidget {
           clipBehavior: Clip.none,
           child: MessageLongPressInkWell(
             key: ValueKey('thread-message-row-${message.id}'),
+            enabled: !selecting,
             onLongPressDetails: openMessageActions,
             borderRadius: BorderRadius.circular(Radii.md),
             highlightColor: context.colors.primary.withValues(alpha: 0.1),
@@ -223,11 +229,21 @@ class _ThreadMessage extends HookConsumerWidget {
                                                 ),
                                           ),
                                         ],
+                                        if (selecting) ...[
+                                          const SizedBox(width: Grid.half),
+                                          const MessageTextSelectionDoneButton(),
+                                        ],
                                       ],
                                     ),
+                                  )
+                                else if (selecting)
+                                  const Align(
+                                    alignment: Alignment.centerRight,
+                                    child: MessageTextSelectionDoneButton(),
                                   ),
                                 MessageContent(
                                   content: message.content,
+                                  selectable: selecting,
                                   mentionNames: resolvedMentionNames,
                                   agentMentionPubkeys: agentMentionPubkeys,
                                   channelNames: channelNames,