feat(mobile): render assistant messages as markdown (#1405)

* feat(mobile): render assistant messages as markdown, keep user text plain

Add flutter_markdown dependency and conditionally render chat bubbles:
- User messages use plain Text to avoid formatting markdown characters
- Assistant messages use MarkdownBody with styled headings, bold, italic,
  lists and code blocks matching the existing color scheme
- Bump Dart SDK constraint to >=3.3.0 to satisfy flutter_markdown 0.7.2

* fix(mobile): address markdown rendering review comments

- Extract MarkdownStyleSheet into _markdownStyle() helper to avoid
  rebuilding TextStyles on every message render
- Replace deprecated imageBuilder with sizedImageBuilder; block http/https
  image URIs to prevent unsolicited remote fetches from AI-generated content
- Commit updated pubspec.lock with flutter_markdown 0.7.2 resolved

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

* Fix tests

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: Juan José Mata <jjmata@jjmata.com>

mobile/lib/screens/chat_conversation_screen.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
+import 'package:flutter_markdown/flutter_markdown.dart';
 import 'package:provider/provider.dart';
 import '../models/chat.dart';
 import '../providers/auth_provider.dart';
@@ -414,6 +415,22 @@ class _MessageBubble extends StatelessWidget {
     required this.formatTime,
   });
 
+  /// Builds the markdown stylesheet once per render context instead of inline,
+  /// avoiding redundant TextStyle allocations per message bubble.
+  MarkdownStyleSheet _markdownStyle(BuildContext context) {
+    final color = Theme.of(context).colorScheme.onSurfaceVariant;
+    return MarkdownStyleSheet.fromTheme(Theme.of(context)).copyWith(
+      p: TextStyle(color: color),
+      strong: TextStyle(color: color, fontWeight: FontWeight.bold),
+      em: TextStyle(color: color, fontStyle: FontStyle.italic),
+      listBullet: TextStyle(color: color),
+      h1: TextStyle(color: color, fontSize: 20, fontWeight: FontWeight.bold),
+      h2: TextStyle(color: color, fontSize: 18, fontWeight: FontWeight.bold),
+      h3: TextStyle(color: color, fontSize: 16, fontWeight: FontWeight.bold),
+      code: TextStyle(color: color, fontFamily: 'monospace'),
+    );
+  }
+
   @override
   Widget build(BuildContext context) {
     final colorScheme = Theme.of(context).colorScheme;
@@ -455,14 +472,27 @@ class _MessageBubble extends StatelessWidget {
                   child: Column(
                     crossAxisAlignment: CrossAxisAlignment.start,
                     children: [
-                      Text(
-                        message.content,
-                        style: TextStyle(
-                          color: isUser
-                              ? colorScheme.onPrimary
-                              : colorScheme.onSurfaceVariant,
+                      if (isUser)
+                        Text(
+                          message.content,
+                          style: TextStyle(
+                            color: colorScheme.onPrimary,
+                          ),
+                        )
+                      else
+                        MarkdownBody(
+                          data: message.content,
+                          selectable: false,
+                          softLineBreak: true,
+                          styleSheet: _markdownStyle(context),
+                          sizedImageBuilder: (config) {
+                            // Block remote images to prevent unsolicited network requests.
+                            if (config.uri.scheme == 'http' || config.uri.scheme == 'https') {
+                              return const SizedBox.shrink();
+                            }
+                            return Image.asset(config.uri.toString());
+                          },
                         ),
-                      ),
                       if (message.toolCalls != null &&
                           message.toolCalls!.isNotEmpty)
                         Padding(

mobile/pubspec.lock

@@ -69,10 +69,10 @@ packages:
     dependency: transitive
     description:
       name: characters
-      sha256: f71061c654a3380576a52b451dd5532377954cf9dbd272a78fc8479606670803
+      sha256: faf38497bda5ead2a8c7615f4f7939df04333478bf32e4173fcb06d428b5716b
       url: "https://pub.dev"
     source: hosted
-    version: "1.4.0"
+    version: "1.4.1"
   checked_yaml:
     dependency: transitive
     description:
@@ -198,6 +198,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "6.0.0"
+  flutter_markdown:
+    dependency: "direct main"
+    description:
+      name: flutter_markdown
+      sha256: "08fb8315236099ff8e90cb87bb2b935e0a724a3af1623000a9cec930468e0f27"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.7.7+1"
   flutter_secure_storage:
     dependency: "direct main"
     description:
@@ -344,22 +352,30 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "6.1.0"
+  markdown:
+    dependency: transitive
+    description:
+      name: markdown
+      sha256: ee85086ad7698b42522c6ad42fe195f1b9898e4d974a1af4576c1a3a176cada9
+      url: "https://pub.dev"
+    source: hosted
+    version: "7.3.1"
   matcher:
     dependency: transitive
     description:
       name: matcher
-      sha256: dc58c723c3c24bf8d3e2d3ad3f2f9d7bd9cf43ec6feaa64181775e60190153f2
+      sha256: "12956d0ad8390bbcc63ca2e1469c0619946ccb52809807067a7020d57e647aa6"
       url: "https://pub.dev"
     source: hosted
-    version: "0.12.17"
+    version: "0.12.18"
   material_color_utilities:
     dependency: transitive
     description:
       name: material_color_utilities
-      sha256: f7142bb1154231d7ea5f96bc7bde4bda2a0945d2806bb11670e30b850d56bdec
+      sha256: "9c337007e82b1889149c82ed242ed1cb24a66044e30979c44912381e9be4c48b"
       url: "https://pub.dev"
     source: hosted
-    version: "0.11.1"
+    version: "0.13.0"
   meta:
     dependency: transitive
     description:
@@ -657,10 +673,10 @@ packages:
     dependency: transitive
     description:
       name: test_api
-      sha256: ab2726c1a94d3176a45960b6234466ec367179b87dd74f1611adb1f3b5fb9d55
+      sha256: "93167629bfc610f71560ab9312acdda4959de4df6fac7492c89ff0d3886f6636"
       url: "https://pub.dev"
     source: hosted
-    version: "0.7.7"
+    version: "0.7.9"
   typed_data:
     dependency: transitive
     description:

mobile/pubspec.yaml

@@ -4,7 +4,7 @@ publish_to: 'none'
 version: 0.6.9+20260402
 
 environment:
-  sdk: '>=3.0.0 <4.0.0'
+  sdk: '>=3.3.0 <4.0.0'
   flutter: '>=3.27.0'
 
 dependencies:
@@ -24,6 +24,7 @@ dependencies:
   url_launcher: ^6.2.5
   flutter_svg: ^2.2.0
   package_info_plus: ^8.0.0
+  flutter_markdown: ^0.7.2
 
 dev_dependencies:
   flutter_test: