feat(post): add create post screen with validation and limits

Create post screen improvements:
- Community picker integration
- URL validation (http/https only)
- Input length limits from backend lexicon (title: 300, content: 10000)
- NSFW toggle with self-labels
- Language selection dropdown
- Navigate to feed after successful post creation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[e-mail]>

lib/screens/home/create_post_screen.dart

···
 import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
 
 import '../../constants/app_colors.dart';
+import '../../models/community.dart';
+import '../../models/post.dart';
+import '../../providers/auth_provider.dart';
+import '../../services/api_exceptions.dart';
+import '../../services/coves_api_service.dart';
+import '../compose/community_picker_screen.dart';
+import 'post_detail_screen.dart';
 
-class CreatePostScreen extends StatelessWidget {
-  const CreatePostScreen({super.key});
+/// Language options for posts
+const Map<String, String> languages = {
+  'en': 'English',
+  'es': 'Spanish',
+  'pt': 'Portuguese',
+  'de': 'German',
+  'fr': 'French',
+  'ja': 'Japanese',
+  'ko': 'Korean',
+  'zh': 'Chinese',
+};
+
+/// Content limits from backend lexicon (social.coves.community.post)
+/// Using grapheme limits as they are the user-facing character counts
+const int kTitleMaxLength = 300;
+const int kContentMaxLength = 10000;
+
+/// Create Post Screen
+///
+/// Full-screen interface for creating a new post in a community.
+///
+/// Features:
+/// - Community selector (required)
+/// - Optional title, URL, thumbnail, and body fields
+/// - Language dropdown and NSFW toggle
+/// - Form validation (at least one of title/body/URL required)
+/// - Loading states and error handling
+/// - Keyboard handling with scroll support
+class CreatePostScreen extends StatefulWidget {
+  const CreatePostScreen({this.onNavigateToFeed, super.key});
+
+  /// Callback to navigate to feed tab (used when in tab navigation)
+  final VoidCallback? onNavigateToFeed;
+
+  @override
+  State<CreatePostScreen> createState() => _CreatePostScreenState();
+}
+
+class _CreatePostScreenState extends State<CreatePostScreen>
+    with WidgetsBindingObserver {
+  // Text controllers
+  final TextEditingController _titleController = TextEditingController();
+  final TextEditingController _urlController = TextEditingController();
+  final TextEditingController _thumbnailController = TextEditingController();
+  final TextEditingController _bodyController = TextEditingController();
+
+  // Scroll and focus
+  final ScrollController _scrollController = ScrollController();
+  final FocusNode _titleFocusNode = FocusNode();
+  final FocusNode _urlFocusNode = FocusNode();
+  final FocusNode _thumbnailFocusNode = FocusNode();
+  final FocusNode _bodyFocusNode = FocusNode();
+  double _lastKeyboardHeight = 0;
+
+  // Form state
+  CommunityView? _selectedCommunity;
+  String _language = 'en';
+  bool _isNsfw = false;
+  bool _isSubmitting = false;
+
+  // Computed state
+  bool get _isFormValid {
+    return _selectedCommunity != null &&
+        (_titleController.text.trim().isNotEmpty ||
+            _bodyController.text.trim().isNotEmpty ||
+            _urlController.text.trim().isNotEmpty);
+  }
+
+  @override
+  void initState() {
+    super.initState();
+    WidgetsBinding.instance.addObserver(this);
+    // Listen to text changes to update button state
+    _titleController.addListener(_onTextChanged);
+    _urlController.addListener(_onTextChanged);
+    _bodyController.addListener(_onTextChanged);
+  }
+
+  @override
+  void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
+    _titleController.dispose();
+    _urlController.dispose();
+    _thumbnailController.dispose();
+    _bodyController.dispose();
+    _scrollController.dispose();
+    _titleFocusNode.dispose();
+    _urlFocusNode.dispose();
+    _thumbnailFocusNode.dispose();
+    _bodyFocusNode.dispose();
+    super.dispose();
+  }
+
+  @override
+  void didChangeMetrics() {
+    super.didChangeMetrics();
+    if (!mounted) {
+      return;
+    }
+
+    final keyboardHeight = View.of(context).viewInsets.bottom;
+
+    // Detect keyboard closing and unfocus all text fields
+    if (_lastKeyboardHeight > 0 && keyboardHeight == 0) {
+      FocusManager.instance.primaryFocus?.unfocus();
+    }
+
+    _lastKeyboardHeight = keyboardHeight;
+  }
+
+  void _onTextChanged() {
+    // Force rebuild to update Post button state
+    setState(() {});
+  }
+
+  Future<void> _selectCommunity() async {
+    final result = await Navigator.push<CommunityView>(
+      context,
+      MaterialPageRoute(
+        builder: (context) => const CommunityPickerScreen(),
+      ),
+    );
+
+    if (result != null && mounted) {
+      setState(() {
+        _selectedCommunity = result;
+      });
+    }
+  }
+
+  Future<void> _handleSubmit() async {
+    if (!_isFormValid || _isSubmitting) {
+      return;
+    }
+
+    setState(() {
+      _isSubmitting = true;
+    });
+
+    try {
+      final authProvider = context.read<AuthProvider>();
+
+      // Create API service with auth
+      final apiService = CovesApiService(
+        tokenGetter: authProvider.getAccessToken,
+        tokenRefresher: authProvider.refreshToken,
+        signOutHandler: authProvider.signOut,
+      );
+
+      // Build embed if URL is provided
+      ExternalEmbedInput? embed;
+      final url = _urlController.text.trim();
+      if (url.isNotEmpty) {
+        // Validate URL
+        final uri = Uri.tryParse(url);
+        if (uri == null ||
+            !uri.hasScheme ||
+            (!uri.scheme.startsWith('http'))) {
+          if (mounted) {
+            ScaffoldMessenger.of(context).showSnackBar(
+              SnackBar(
+                content: const Text('Please enter a valid URL (http or https)'),
+                backgroundColor: Colors.red[700],
+                behavior: SnackBarBehavior.floating,
+              ),
+            );
+          }
+          setState(() {
+            _isSubmitting = false;
+          });
+          return;
+        }
+
+        embed = ExternalEmbedInput(
+          uri: url,
+          title: _titleController.text.trim().isNotEmpty
+              ? _titleController.text.trim()
+              : null,
+          thumb: _thumbnailController.text.trim().isNotEmpty
+              ? _thumbnailController.text.trim()
+              : null,
+        );
+      }
+
+      // Build labels if NSFW is enabled
+      SelfLabels? labels;
+      if (_isNsfw) {
+        labels = const SelfLabels(values: [SelfLabel(val: 'nsfw')]);
+      }
+
+      // Create post
+      final response = await apiService.createPost(
+        community: _selectedCommunity!.did,
+        title: _titleController.text.trim().isNotEmpty
+            ? _titleController.text.trim()
+            : null,
+        content: _bodyController.text.trim().isNotEmpty
+            ? _bodyController.text.trim()
+            : null,
+        embed: embed,
+        langs: [_language],
+        labels: labels,
+      );
+
+      if (mounted) {
+        // Build optimistic post for immediate display
+        final optimisticPost = _buildOptimisticPost(
+          response: response,
+          authProvider: authProvider,
+        );
+
+        // Reset form first
+        _resetForm();
+
+        // Navigate to post detail with optimistic data
+        await Navigator.push(
+          context,
+          MaterialPageRoute(
+            builder: (context) => PostDetailScreen(
+              post: optimisticPost,
+              isOptimistic: true,
+            ),
+          ),
+        );
+      }
+    } on ApiException catch (e) {
+      if (mounted) {
+        ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(
+            content: Text('Failed to create post: ${e.message}'),
+            backgroundColor: Colors.red[700],
+            behavior: SnackBarBehavior.floating,
+          ),
+        );
+      }
+    } on Exception catch (e) {
+      if (mounted) {
+        ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(
+            content: Text('Failed to create post: ${e.toString()}'),
+            backgroundColor: Colors.red[700],
+            behavior: SnackBarBehavior.floating,
+          ),
+        );
+      }
+    } finally {
+      if (mounted) {
+        setState(() {
+          _isSubmitting = false;
+        });
+      }
+    }
+  }
+
+  void _resetForm() {
+    setState(() {
+      _titleController.clear();
+      _urlController.clear();
+      _thumbnailController.clear();
+      _bodyController.clear();
+      _selectedCommunity = null;
+      _language = 'en';
+      _isNsfw = false;
+    });
+  }
+
+  /// Build optimistic post for immediate display after creation
+  FeedViewPost _buildOptimisticPost({
+    required CreatePostResponse response,
+    required AuthProvider authProvider,
+  }) {
+    // Extract rkey from AT-URI (at://did/collection/rkey)
+    final uriParts = response.uri.split('/');
+    final rkey = uriParts.isNotEmpty ? uriParts.last : '';
+
+    // Build embed if URL was provided
+    PostEmbed? embed;
+    final url = _urlController.text.trim();
+    if (url.isNotEmpty) {
+      embed = PostEmbed(
+        type: 'social.coves.embed.external',
+        external: ExternalEmbed(
+          uri: url,
+          title: _titleController.text.trim().isNotEmpty
+              ? _titleController.text.trim()
+              : null,
+          thumb: _thumbnailController.text.trim().isNotEmpty
+              ? _thumbnailController.text.trim()
+              : null,
+        ),
+        data: {
+          r'$type': 'social.coves.embed.external',
+          'external': {
+            'uri': url,
+            if (_titleController.text.trim().isNotEmpty)
+              'title': _titleController.text.trim(),
+            if (_thumbnailController.text.trim().isNotEmpty)
+              'thumb': _thumbnailController.text.trim(),
+          },
+        },
+      );
+    }
+
+    final now = DateTime.now();
+
+    return FeedViewPost(
+      post: PostView(
+        uri: response.uri,
+        cid: response.cid,
+        rkey: rkey,
+        author: AuthorView(
+          did: authProvider.did ?? '',
+          handle: authProvider.handle ?? 'unknown',
+          displayName: null,
+          avatar: null,
+        ),
+        community: CommunityRef(
+          did: _selectedCommunity!.did,
+          name: _selectedCommunity!.name,
+          handle: _selectedCommunity!.handle,
+          avatar: _selectedCommunity!.avatar,
+        ),
+        createdAt: now,
+        indexedAt: now,
+        text: _bodyController.text.trim(),
+        title: _titleController.text.trim().isNotEmpty
+            ? _titleController.text.trim()
+            : null,
+        stats: PostStats(
+          upvotes: 0,
+          downvotes: 0,
+          score: 0,
+          commentCount: 0,
+        ),
+        embed: embed,
+        viewer: ViewerState(),
+      ),
+    );
+  }
 
   @override
   Widget build(BuildContext context) {
-    return Scaffold(
-      backgroundColor: const Color(0xFF0B0F14),
-      appBar: AppBar(
-        backgroundColor: const Color(0xFF0B0F14),
-        foregroundColor: Colors.white,
+    final authProvider = context.watch<AuthProvider>();
+    final userHandle = authProvider.handle ?? 'Unknown';
+
+    return PopScope(
+      canPop: widget.onNavigateToFeed == null,
+      onPopInvokedWithResult: (didPop, result) {
+        if (!didPop && widget.onNavigateToFeed != null) {
+          widget.onNavigateToFeed!();
+        }
+      },
+      child: Scaffold(
+        backgroundColor: AppColors.background,
+        appBar: AppBar(
+        backgroundColor: AppColors.background,
+        surfaceTintColor: Colors.transparent,
+        foregroundColor: AppColors.textPrimary,
         title: const Text('Create Post'),
+        elevation: 0,
         automaticallyImplyLeading: false,
+        leading: IconButton(
+          icon: const Icon(Icons.close),
+          onPressed: () {
+            // Use callback if available (tab navigation), otherwise pop
+            if (widget.onNavigateToFeed != null) {
+              widget.onNavigateToFeed!();
+            } else {
+              Navigator.pop(context);
+            }
+          },
+        ),
+        actions: [
+          Padding(
+            padding: const EdgeInsets.only(right: 8),
+            child: TextButton(
+              onPressed: _isFormValid && !_isSubmitting ? _handleSubmit : null,
+              style: TextButton.styleFrom(
+                backgroundColor: _isFormValid && !_isSubmitting
+                    ? AppColors.primary
+                    : AppColors.textSecondary.withValues(alpha: 0.3),
+                foregroundColor: AppColors.textPrimary,
+                padding: const EdgeInsets.symmetric(
+                  horizontal: 16,
+                  vertical: 8,
+                ),
+                shape: RoundedRectangleBorder(
+                  borderRadius: BorderRadius.circular(20),
+                ),
+              ),
+              child:
+                  _isSubmitting
+                      ? const SizedBox(
+                        width: 16,
+                        height: 16,
+                        child: CircularProgressIndicator(
+                          strokeWidth: 2,
+                          valueColor: AlwaysStoppedAnimation<Color>(
+                            AppColors.textPrimary,
+                          ),
+                        ),
+                      )
+                      : const Text('Post'),
+            ),
+          ),
+        ],
       ),
-      body: const Center(
-        child: Padding(
-          padding: EdgeInsets.all(24),
+      body: SafeArea(
+        child: SingleChildScrollView(
+          controller: _scrollController,
+          padding: const EdgeInsets.all(16),
           child: Column(
-            mainAxisAlignment: MainAxisAlignment.center,
+            crossAxisAlignment: CrossAxisAlignment.stretch,
             children: [
-              Icon(
-                Icons.add_circle_outline,
-                size: 64,
-                color: AppColors.primary,
+              // Community selector
+              _buildCommunitySelector(),
+
+              const SizedBox(height: 16),
+
+              // User info row
+              _buildUserInfo(userHandle),
+
+              const SizedBox(height: 24),
+
+              // Title field
+              _buildTextField(
+                controller: _titleController,
+                focusNode: _titleFocusNode,
+                hintText: 'Title',
+                maxLines: 1,
+                maxLength: kTitleMaxLength,
+              ),
+
+              const SizedBox(height: 16),
+
+              // URL field
+              _buildTextField(
+                controller: _urlController,
+                focusNode: _urlFocusNode,
+                hintText: 'URL',
+                maxLines: 1,
+                keyboardType: TextInputType.url,
               ),
-              SizedBox(height: 24),
-              Text(
-                'Create Post',
-                style: TextStyle(
-                  fontSize: 28,
-                  color: Colors.white,
-                  fontWeight: FontWeight.bold,
+
+              // Thumbnail field (only visible when URL is filled)
+              if (_urlController.text.trim().isNotEmpty) ...[
+                const SizedBox(height: 16),
+                _buildTextField(
+                  controller: _thumbnailController,
+                  focusNode: _thumbnailFocusNode,
+                  hintText: 'Thumbnail URL',
+                  maxLines: 1,
+                  keyboardType: TextInputType.url,
                 ),
+              ],
+
+              const SizedBox(height: 16),
+
+              // Body field (multiline)
+              _buildTextField(
+                controller: _bodyController,
+                focusNode: _bodyFocusNode,
+                hintText: 'What are your thoughts?',
+                minLines: 8,
+                maxLines: null,
+                maxLength: kContentMaxLength,
               ),
-              SizedBox(height: 16),
-              Text(
-                'Share your thoughts with the community',
-                style: TextStyle(fontSize: 16, color: Color(0xFFB6C2D2)),
-                textAlign: TextAlign.center,
+
+              const SizedBox(height: 24),
+
+              // Language dropdown and NSFW toggle
+              Row(
+                children: [
+                  // Language dropdown
+                  Expanded(
+                    child: _buildLanguageDropdown(),
+                  ),
+
+                  const SizedBox(width: 16),
+
+                  // NSFW toggle
+                  Expanded(
+                    child: _buildNsfwToggle(),
+                  ),
+                ],
               ),
+
+              const SizedBox(height: 24),
             ],
           ),
         ),
+      ),
+      ),
+    );
+  }
+
+  Widget _buildCommunitySelector() {
+    return Material(
+      color: Colors.transparent,
+      child: InkWell(
+        onTap: _selectCommunity,
+        borderRadius: BorderRadius.circular(12),
+        child: Container(
+          padding: const EdgeInsets.all(16),
+          decoration: BoxDecoration(
+            color: AppColors.backgroundSecondary,
+            border: Border.all(color: AppColors.border),
+            borderRadius: BorderRadius.circular(12),
+          ),
+          child: Row(
+            children: [
+              const Icon(
+                Icons.workspaces_outlined,
+                color: AppColors.textSecondary,
+                size: 20,
+              ),
+              const SizedBox(width: 12),
+              Expanded(
+                child: Text(
+                  _selectedCommunity?.displayName ??
+                      _selectedCommunity?.name ??
+                      'Select a community',
+                  style:
+                      TextStyle(
+                        color:
+                            _selectedCommunity != null
+                                ? AppColors.textPrimary
+                                : AppColors.textSecondary,
+                        fontSize: 16,
+                      ),
+                  maxLines: 1,
+                  overflow: TextOverflow.ellipsis,
+                ),
+              ),
+              const Icon(
+                Icons.chevron_right,
+                color: AppColors.textSecondary,
+                size: 20,
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+
+  Widget _buildUserInfo(String handle) {
+    return Row(
+      children: [
+        const Icon(
+          Icons.person,
+          color: AppColors.textSecondary,
+          size: 16,
+        ),
+        const SizedBox(width: 8),
+        Text(
+          '@$handle',
+          style: const TextStyle(
+            color: AppColors.textSecondary,
+            fontSize: 14,
+          ),
+        ),
+      ],
+    );
+  }
+
+  Widget _buildTextField({
+    required TextEditingController controller,
+    required String hintText,
+    FocusNode? focusNode,
+    int? maxLines,
+    int? minLines,
+    int? maxLength,
+    TextInputType? keyboardType,
+    TextInputAction? textInputAction,
+  }) {
+    // For multiline fields, use newline action and multiline keyboard
+    final isMultiline = minLines != null && minLines > 1;
+    final effectiveKeyboardType =
+        keyboardType ?? (isMultiline ? TextInputType.multiline : TextInputType.text);
+    final effectiveTextInputAction =
+        textInputAction ?? (isMultiline ? TextInputAction.newline : TextInputAction.next);
+
+    return TextField(
+      controller: controller,
+      focusNode: focusNode,
+      maxLines: maxLines,
+      minLines: minLines,
+      maxLength: maxLength,
+      keyboardType: effectiveKeyboardType,
+      textInputAction: effectiveTextInputAction,
+      textCapitalization: TextCapitalization.sentences,
+      style: const TextStyle(
+        color: AppColors.textPrimary,
+        fontSize: 16,
+      ),
+      decoration: InputDecoration(
+        hintText: hintText,
+        hintStyle: const TextStyle(color: Color(0xFF5A6B7F)),
+        filled: true,
+        fillColor: const Color(0xFF1A2028),
+        counterStyle: const TextStyle(color: AppColors.textSecondary),
+        border: OutlineInputBorder(
+          borderRadius: BorderRadius.circular(12),
+          borderSide: const BorderSide(color: Color(0xFF2A3441)),
+        ),
+        enabledBorder: OutlineInputBorder(
+          borderRadius: BorderRadius.circular(12),
+          borderSide: const BorderSide(color: Color(0xFF2A3441)),
+        ),
+        focusedBorder: OutlineInputBorder(
+          borderRadius: BorderRadius.circular(12),
+          borderSide: const BorderSide(
+            color: AppColors.primary,
+            width: 2,
+          ),
+        ),
+        contentPadding: const EdgeInsets.all(16),
+      ),
+    );
+  }
+
+  Widget _buildLanguageDropdown() {
+    return Container(
+      padding: const EdgeInsets.symmetric(horizontal: 12),
+      decoration: BoxDecoration(
+        color: AppColors.backgroundSecondary,
+        border: Border.all(color: AppColors.border),
+        borderRadius: BorderRadius.circular(12),
+      ),
+      child: DropdownButtonHideUnderline(
+        child: DropdownButton<String>(
+          value: _language,
+          dropdownColor: AppColors.backgroundSecondary,
+          style: const TextStyle(
+            color: AppColors.textPrimary,
+            fontSize: 16,
+          ),
+          icon: const Icon(
+            Icons.arrow_drop_down,
+            color: AppColors.textSecondary,
+          ),
+          items:
+              languages.entries.map((entry) {
+                return DropdownMenuItem<String>(
+                  value: entry.key,
+                  child: Text(entry.value),
+                );
+              }).toList(),
+          onChanged: (value) {
+            if (value != null) {
+              setState(() {
+                _language = value;
+              });
+            }
+          },
+        ),
+      ),
+    );
+  }
+
+  Widget _buildNsfwToggle() {
+    return Container(
+      padding: const EdgeInsets.symmetric(horizontal: 12),
+      decoration: BoxDecoration(
+        color: AppColors.backgroundSecondary,
+        border: Border.all(color: AppColors.border),
+        borderRadius: BorderRadius.circular(12),
+      ),
+      child: Row(
+        mainAxisAlignment: MainAxisAlignment.spaceBetween,
+        children: [
+          const Text(
+            'NSFW',
+            style: TextStyle(
+              color: AppColors.textPrimary,
+              fontSize: 16,
+            ),
+          ),
+          Transform.scale(
+            scale: 0.8,
+            child: Switch.adaptive(
+              value: _isNsfw,
+              activeTrackColor: AppColors.primary,
+              onChanged: (value) {
+                setState(() {
+                  _isNsfw = value;
+                });
+              },
+            ),
+          ),
+        ],
       ),
     );
   }

lib/screens/home/main_shell_screen.dart

···
     });
   }
 
+  void _onNavigateToFeed() {
+    setState(() {
+      _selectedIndex = 0; // Switch to feed tab
+    });
+  }
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
···
         children: [
           FeedScreen(onSearchTap: _onCommunitiesTap),
           const CommunitiesScreen(),
-          const CreatePostScreen(),
+          CreatePostScreen(onNavigateToFeed: _onNavigateToFeed),
           const NotificationsScreen(),
           const ProfileScreen(),
         ],