Merge branch 'fix/flutter-code-review-findings-2026-03-05' into v3.0

.env/flutter_defines.example.json

@@ -0,0 +1,5 @@
+{
+  "SUPABASE_URL": "https://your-project.supabase.co",
+  "SUPABASE_ANON_KEY": "your_anon_key",
+  "SUPABASE_USE_PKCE": "true"
+}

.gitignore

@@ -48,6 +48,10 @@ app.*.map.json
 /supabase_migration.sql
 /TPB_APP_CHECKLIST.md
 
+# Local run configuration with secrets
+/.vscode/launch.json
+/.env/flutter_defines.json
+
 # Local testing artifacts
 /flutter_*.png
 /devtools_options.yaml

.vscode/tasks.json

@@ -0,0 +1,44 @@
+{
+  "version": "2.0.0",
+  "tasks": [
+    {
+      "label": "Flutter Build APK (Release)",
+      "type": "shell",
+      "command": "flutter",
+      "args": [
+        "build",
+        "apk",
+        "--release",
+        "--dart-define-from-file=.env/flutter_defines.json"
+      ],
+      "group": "build",
+      "problemMatcher": []
+    },
+    {
+      "label": "Flutter Build App Bundle (Release)",
+      "type": "shell",
+      "command": "flutter",
+      "args": [
+        "build",
+        "appbundle",
+        "--release",
+        "--dart-define-from-file=.env/flutter_defines.json"
+      ],
+      "group": "build",
+      "problemMatcher": []
+    },
+    {
+      "label": "Flutter Build iOS IPA (Release)",
+      "type": "shell",
+      "command": "flutter",
+      "args": [
+        "build",
+        "ipa",
+        "--release",
+        "--dart-define-from-file=.env/flutter_defines.json"
+      ],
+      "group": "build",
+      "problemMatcher": []
+    }
+  ]
+}

CONTRIBUTING.md

@@ -0,0 +1,52 @@
+# Contributing Guide
+
+Thanks for contributing to car64.
+
+## Workflow
+
+- Create a branch from `main`:
+  - `feature/<short-name>` for features
+  - `fix/<short-name>` for bug fixes
+  - `docs/<short-name>` for documentation updates
+- Keep pull requests focused and small when possible.
+- Write clear commit messages (Conventional Commit style is preferred).
+
+## Development Setup
+
+1. Install Flutter stable and run `flutter doctor`.
+2. Copy `.env/flutter_defines.example.json` to `.env/flutter_defines.json`.
+3. Fill in your own Supabase config values.
+4. Run:
+
+```bash
+flutter pub get
+flutter analyze
+```
+
+## Code Style
+
+- Follow existing project style and naming patterns.
+- Prefer small, explicit methods over deeply nested logic.
+- Preserve backend contract names (`hotwheels`, RPC names, etc.) unless migration is intentional.
+
+## Testing & Validation
+
+Before opening a PR:
+
+- Run `flutter analyze`
+- Run available tests
+- Manually test affected flows (scanner, collections, auth, storage upload)
+
+## Pull Request Checklist
+
+- [ ] Scope is clear and focused
+- [ ] Analyzer passes
+- [ ] User-facing strings are intentional and reviewed
+- [ ] No secrets/config values were committed
+- [ ] README/docs updated if behavior changed
+
+## Commit Message Examples
+
+- `fix(scanner): prevent duplicate processing on repeated detections`
+- `perf(collections): coalesce overlapping reload requests`
+- `docs(readme): add release workflow section`

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Lukas Müllner @derkauzigekoala
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -1,38 +1,193 @@
-# car64
+<p align="center">
+  <img src="assets/icon/app_icon.png" alt="car64 logo" width="120" />
+</p>
 
-car64 is a Flutter + Supabase Hot Wheels collector app with a fast scanning workflow, private photo storage, collaborative collections, and community-based catalog validation.
+<h1 align="center">car64</h1>
 
-## Core Features
+<p align="center">
+  A modern Flutter + Supabase app for tracking and managing die-cast car collections.
+</p>
 
-- Lightning add flow with barcode/OCR scanning and active collection selection.
+---
-- Global catalog (`global_cars`) + personal entries (`hotwheels`) architecture.
-- Private storage (`car-images`) with signed URL rendering for collection members.
-- In-app photo compression pipeline (target max 1080px and <500 KB uploads).
-- Collaborative garages via `collections` + `collection_members`.
-- Community validation with `car_votes`, `confirmation_count`, and verification state.
 
-## Local Development
+## Table of Contents
 
-1. Install Flutter (stable) and run `flutter doctor`.
+- [Overview](#overview)
-2. Configure Supabase keys in app configuration.
+- [Features](#features)
-3. Install dependencies:
+- [Tech Stack](#tech-stack)
+- [Prerequisites](#prerequisites)
+- [Configuration](#configuration)
+- [Getting Started](#getting-started)
+- [VS Code Workflows](#vs-code-workflows)
+- [Project Structure (high level)](#project-structure-high-level)
+- [Troubleshooting](#troubleshooting)
+- [Release Checklist](#release-checklist)
+- [Roadmap](#roadmap)
+- [Contributing](#contributing)
+- [Security Notes](#security-notes)
+- [License](#license)
+- [Reference](#reference)
 
-	```bash
+## Overview
-	flutter pub get
-	```
 
-4. Run the app:
+car64 helps collectors scan model IDs, organize personal and shared collections, and keep a clean catalog with community validation/reporting flows.
 
-	```bash
+## Features
-	flutter run
-	```
 
-## Quality Check
+- Fast scan workflow (camera OCR + manual entry fallback)
+- Multi-collection support with member roles (owner/member/viewer)
+- Private image storage with signed URL access
+- Collection collaboration and member management
+- Community validation and issue reporting for catalog entries
+- Profile/settings flows including password updates and report tracking
+
+## Tech Stack
+
+- Flutter (Material 3)
+- Supabase (Auth, PostgREST, Storage, RPC)
+- Shared Preferences (local settings)
+- Google ML Kit Text Recognition (scanner)
+
+## Prerequisites
+
+- Flutter SDK (stable)
+- A Supabase project
+- For iOS builds: macOS + Xcode
+
+## Configuration
+
+Supabase config is required at runtime/build time (no embedded fallback values).
+
+### Option A: local defines file (recommended)
+
+Use:
+
+- `.env/flutter_defines.json` (local, ignored by git)
+- `.env/flutter_defines.example.json` (tracked template)
+
+Expected shape:
+
+```json
+{
+  "SUPABASE_URL": "https://your-project.supabase.co",
+  "SUPABASE_ANON_KEY": "your_anon_key",
+  "SUPABASE_USE_PKCE": "true"
+}
+```
+
+### Option B: direct dart-define flags
+
+```bash
+flutter run \
+  --dart-define=SUPABASE_URL=https://your-project.supabase.co \
+  --dart-define=SUPABASE_ANON_KEY=your_anon_key \
+  --dart-define=SUPABASE_USE_PKCE=true
+```
+
+## Getting Started
+
+1. Install dependencies
+
+```bash
+flutter pub get
+```
+
+2. Run analyze
 
 ```bash
 flutter analyze
 ```
 
+3. Launch app
+
+```bash
+flutter run
+```
+
+## VS Code Workflows
+
+### Run / Debug (`launch.json`)
+
+Use **Run and Debug** with:
+
+- `Flutter (Supabase Local - Debug)`
+- `Flutter (Supabase Local - Profile)`
+- `Flutter (Supabase Local - Release)`
+
+These configurations read:
+
+`--dart-define-from-file=.env/flutter_defines.json`
+
+### Build Tasks (`tasks.json`)
+
+Use **Terminal → Run Task**:
+
+- `Flutter Build APK (Release)`
+- `Flutter Build App Bundle (Release)`
+- `Flutter Build iOS IPA (Release)`
+
+## Project Structure (high level)
+
+- `lib/screens/` UI screens and flows
+- `lib/services/` Supabase integration/services
+- `lib/widgets/` reusable UI components
+- `lib/utils/` helpers and formatting utilities
+- `lib/theme/` app theme and colors
+
+## Troubleshooting
+
+### App fails at startup with Supabase config error
+
+- Ensure `.env/flutter_defines.json` exists locally.
+- Confirm all required keys are present:
+  - `SUPABASE_URL`
+  - `SUPABASE_ANON_KEY`
+  - `SUPABASE_USE_PKCE`
+
+### Build task works but app cannot connect to backend
+
+- Verify the Supabase URL/key pair belong to the same project.
+- Check Supabase RLS policies and RPC permissions.
+
+### iOS IPA task fails on Windows
+
+- `flutter build ipa` requires macOS + Xcode.
+
+## Release Checklist
+
+- [ ] `flutter pub get`
+- [ ] `flutter analyze`
+- [ ] Manual smoke test on Android
+- [ ] Manual smoke test on iOS
+- [ ] Confirm `.env/flutter_defines.json` points to production Supabase
+- [ ] Build Android `appbundle`
+- [ ] Build iOS `ipa`
+- [ ] Verify auth, scan flow, collections, and upload flows
+
+## Roadmap
+
+- [ ] Optional dark/light theme toggle in settings
+- [ ] Extended scanner confidence hints and retry UX
+- [ ] Bulk actions and better collection analytics
+- [ ] Improved offline behavior for low-connectivity sessions
+
+## Contributing
+
+See `CONTRIBUTING.md` for branching, commit style, and PR guidelines.
+
+## Security Notes
+
+- Supabase anon keys are intentionally client-side, but RLS and RPC permissions must be strict.
+- Sensitive local config files are git-ignored.
+- User-facing errors are sanitized and shown via global overlays.
+
+For reporting vulnerabilities, see `SECURITY.md`.
+
+## License
+
+License file is not included in this repository yet.
+Add your preferred license in the GitHub repo when ready.
+
 ## Reference
 
-- Product and backend requirements: `TPB.md`
+- Product/backend notes: `TPB.md`

SECURITY.md

@@ -0,0 +1,31 @@
+# Security Policy
+
+## Supported Versions
+
+This project currently supports the latest active branch in this repository.
+
+## Reporting a Vulnerability
+
+If you discover a security issue, please do not open a public issue with exploit details.
+
+Preferred process:
+
+1. Share a private report with:
+   - A clear description of the issue
+   - Reproduction steps
+   - Impact assessment
+   - Suggested fix (if available)
+2. Allow time for triage and remediation before public disclosure.
+
+## Scope Notes
+
+- Supabase anon keys are client-side by design and are not secret credentials.
+- Real protection depends on strict RLS policies, RPC authorization, and server-side validation.
+- Local config files with runtime values should stay out of version control.
+
+## Recommended Hardening
+
+- Keep Supabase keys in local/CI `dart-define` configuration only.
+- Rotate keys when moving between environments or if misuse is suspected.
+- Audit RLS policies after every schema/function change.
+- Sanitize user-facing error messages (avoid leaking backend internals).

lib/main.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 import 'package:supabase_flutter/supabase_flutter.dart';
@@ -6,23 +8,44 @@ import 'services/collection_service.dart';
 import 'services/main_collection_sync.dart';
 import 'screens/login_screen.dart';
 import 'screens/home_shell.dart';
+import 'utils/error_utils.dart';
+import 'utils/preferences_utils.dart';
 
 // Re-export so other files can `import '../main.dart'` for these.
 export 'package:supabase_flutter/supabase_flutter.dart'
     show AuthException, UserAttributes;
 
 // ── Supabase credentials ──────────────────────────────────────────────
-const _supabaseUrl = 'https://yaopcyubateifnicpywp.supabase.co';
+const _supabaseUrl = String.fromEnvironment(
-const _supabaseAnonKey = 'sb_publishable_a7czIl7-TGeBJvid9z2XZA_3ElImliL';
+  'SUPABASE_URL',
+  defaultValue: '',
+);
+const _supabaseAnonKey = String.fromEnvironment(
+  'SUPABASE_ANON_KEY',
+  defaultValue: '',
+);
+const _usePkceAuthFlow = bool.fromEnvironment(
+  'SUPABASE_USE_PKCE',
+  defaultValue: true,
+);
 
 Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
 
+  if (_supabaseUrl.trim().isEmpty || _supabaseAnonKey.trim().isEmpty) {
+    throw StateError(
+      'Missing Supabase configuration. Provide --dart-define=SUPABASE_URL and '
+      '--dart-define=SUPABASE_ANON_KEY.',
+    );
+  }
+
   await Supabase.initialize(
     url: _supabaseUrl,
     anonKey: _supabaseAnonKey,
-    authOptions: const FlutterAuthClientOptions(
+    authOptions: FlutterAuthClientOptions(
-      authFlowType: AuthFlowType.implicit,
+      authFlowType: _usePkceAuthFlow
+          ? AuthFlowType.pkce
+          : AuthFlowType.implicit,
     ),
   );
 
@@ -35,29 +58,121 @@ final supabase = Supabase.instance.client;
 /// Global keys so dialogs & snackbars survive widget-tree rebuilds.
 final navigatorKey = GlobalKey<NavigatorState>();
 final scaffoldMessengerKey = GlobalKey<ScaffoldMessengerState>();
+OverlayEntry? _activeMessageOverlay;
+Timer? _activeMessageOverlayTimer;
+
+enum GlobalMessageType { info, success, error }
 
 /// Show a snackbar safely through the global key.
 void showGlobalSnackBar(String message, {bool isError = false}) {
-  final messenger = scaffoldMessengerKey.currentState;
+  _showGlobalMessageOverlay(
-  if (messenger == null) return;
+    message,
+    type: isError ? GlobalMessageType.error : GlobalMessageType.info,
+  );
+}
 
-  messenger
+void showGlobalSuccess(String message) {
-    ..hideCurrentSnackBar()
+  _showGlobalMessageOverlay(message, type: GlobalMessageType.success);
-    ..showSnackBar(
+}
-    SnackBar(
+
-      content: Text(message),
+void showGlobalInfo(String message) {
-      backgroundColor: isError ? Colors.red : null,
+  _showGlobalMessageOverlay(message, type: GlobalMessageType.info);
-      behavior: SnackBarBehavior.floating,
+}
-      margin: const EdgeInsets.fromLTRB(16, 0, 16, 96),
+
-      duration: const Duration(seconds: 3),
+void _showGlobalMessageOverlay(
+  String message, {
+  required GlobalMessageType type,
+}) {
+  final overlay = navigatorKey.currentState?.overlay;
+  if (overlay == null) return;
+
+  _activeMessageOverlayTimer?.cancel();
+  _activeMessageOverlay?.remove();
+
+  final backgroundColor = switch (type) {
+    GlobalMessageType.error => Colors.red,
+    GlobalMessageType.success => Colors.green,
+    GlobalMessageType.info => const Color(0xFF1F2937),
+  };
+  final leadingIcon = switch (type) {
+    GlobalMessageType.error => Icons.error_outline,
+    GlobalMessageType.success => Icons.check_circle_outline,
+    GlobalMessageType.info => Icons.info_outline,
+  };
+
+  _activeMessageOverlay = OverlayEntry(
+    builder: (context) {
+      final topPadding = MediaQuery.of(context).padding.top;
+      return Positioned(
+        top: topPadding + 12,
+        left: 12,
+        right: 12,
+        child: Material(
+          color: Colors.transparent,
+          child: IgnorePointer(
+            ignoring: true,
+            child: Container(
+              padding: const EdgeInsets.symmetric(horizontal: 14, vertical: 12),
+              decoration: BoxDecoration(
+                color: backgroundColor,
+                borderRadius: BorderRadius.circular(12),
+                boxShadow: const [
+                  BoxShadow(
+                    color: Colors.black26,
+                    blurRadius: 8,
+                    offset: Offset(0, 3),
                   ),
+                ],
+              ),
+              child: Row(
+                children: [
+                  Icon(leadingIcon, color: Colors.white, size: 20),
+                  const SizedBox(width: 8),
+                  Expanded(
+                    child: Text(
+                      message,
+                      style: const TextStyle(color: Colors.white),
+                      maxLines: 3,
+                      overflow: TextOverflow.ellipsis,
+                    ),
+                  ),
+                ],
+              ),
+            ),
+          ),
+        ),
+      );
+    },
+  );
+
+  overlay.insert(_activeMessageOverlay!);
+
+  _activeMessageOverlayTimer = Timer(const Duration(seconds: 4), () {
+    _activeMessageOverlay?.remove();
+    _activeMessageOverlay = null;
+    _activeMessageOverlayTimer = null;
+  });
+}
+
+void showGlobalError(
+  Object error, {
+  String fallback = 'Something went wrong. Please try again.',
+}) {
+  logError('ui', error);
+  showGlobalSnackBar(
+    userMessageForError(error, fallback: fallback),
+    isError: true,
   );
 }
 
 /// Show a dialog safely through the global navigator key.
 Future<T?> showGlobalDialog<T>({required WidgetBuilder builder}) {
+  final context = navigatorKey.currentContext;
+  if (context == null) {
+    return Future<T?>.value(null);
+  }
   return showDialog<T>(
-    context: navigatorKey.currentContext!,
+    context: context,
     builder: builder,
   );
 }
@@ -90,8 +205,6 @@ class AuthGate extends StatefulWidget {
 }
 
 class _AuthGateState extends State<AuthGate> {
-  static const _activeCollectionPrefKey = 'active_collection_id';
-
   bool _isLoading = true;
   bool _isInPasswordRecoveryFlow = false;
   Session? _session;
@@ -124,7 +237,10 @@ class _AuthGateState extends State<AuthGate> {
         }
       },
       onError: (error) {
-        showGlobalSnackBar('Auth error: $error', isError: true);
+        showGlobalError(
+          error,
+          fallback: 'Authentication error. Please sign in again.',
+        );
       },
     );
 
@@ -140,7 +256,10 @@ class _AuthGateState extends State<AuthGate> {
       final defaultCollectionId = await CollectionService.ensureDefaultCollection();
       await _ensureMainCollectionPreference(defaultCollectionId);
     } catch (e) {
-      showGlobalSnackBar('Collection setup failed: $e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Collection setup failed. Please try again.',
+      );
     }
   }
 
@@ -149,7 +268,7 @@ class _AuthGateState extends State<AuthGate> {
     if (userId == null) return;
 
     final prefs = await SharedPreferences.getInstance();
-    final persisted = prefs.getString(_activeCollectionPrefKey);
+    final persisted = await readActiveCollectionId(prefs, userId: userId);
 
     Future<bool> hasMembership(String collectionId) async {
       final membership = await supabase
@@ -180,17 +299,27 @@ class _AuthGateState extends State<AuthGate> {
     }
 
     if (nextActiveId == null) {
-      await prefs.remove(_activeCollectionPrefKey);
+      await clearActiveCollectionId(prefs, userId: userId);
       return;
     }
 
-    await prefs.setString(_activeCollectionPrefKey, nextActiveId);
+    await writeActiveCollectionId(
+      prefs,
+      userId: userId,
+      collectionId: nextActiveId,
+    );
     MainCollectionSync.notifyChanged();
   }
 
   Future<void> _showResetPasswordDialog() async {
+    final context = navigatorKey.currentContext;
+    if (context == null) {
+      _isInPasswordRecoveryFlow = false;
+      return;
+    }
+
     await showDialog<void>(
-      context: navigatorKey.currentContext!,
+      context: context,
       barrierDismissible: false,
       builder: (_) => const _ResetPasswordDialog(),
     );
@@ -245,7 +374,7 @@ class _ResetPasswordDialogState extends State<_ResetPasswordDialog> {
       );
       if (!mounted) return;
       Navigator.of(context).pop();
-      showGlobalSnackBar('Password updated successfully!');
+      showGlobalSuccess('Password updated successfully!');
     } on AuthException catch (e) {
       if (!mounted) return;
       setState(() => _isSaving = false);

lib/scanner_screen.dart

@@ -6,9 +6,10 @@ import 'package:camera/camera.dart';
 import 'package:google_mlkit_text_recognition/google_mlkit_text_recognition.dart';
 import 'services/collection_service.dart';
 import 'theme/app_colors.dart';
+import 'utils/error_utils.dart';
 import 'utils/scanner_utils.dart';
 
-/// Screen that uses the camera to scan text (OCR) from a Hot Wheels package
+/// Screen that uses the camera to scan text (OCR) from a die-cast package
 /// and extract the hw_id (e.g. "JKF21").
 ///
 /// The detected ID is returned via Navigator.pop(context, hwId).
@@ -36,6 +37,7 @@ class _ScannerScreenState extends State<ScannerScreen>
   static const _scanCooldownSuccess = Duration(milliseconds: 1500);
   static const _scanCooldownNoMatch = Duration(milliseconds: 2200);
   static const _scanCooldownError = Duration(milliseconds: 2600);
+  static const _scanCooldownNoMatchMax = Duration(milliseconds: 5000);
 
   CameraController? _cameraController;
   late final TextRecognizer _textRecognizer;
@@ -51,6 +53,7 @@ class _ScannerScreenState extends State<ScannerScreen>
   DateTime _nextScanAllowedAt = DateTime.fromMillisecondsSinceEpoch(0);
   bool _isInitializingCamera = false;
   String? _cameraError;
+  int _consecutiveMisses = 0;
 
   @override
   void initState() {
@@ -126,9 +129,15 @@ class _ScannerScreenState extends State<ScannerScreen>
         _cameraError = 'Camera unavailable. Please retry.';
         _statusText = 'Camera unavailable';
       });
+      logError('scanner.initCamera', e);
       ScaffoldMessenger.of(context).showSnackBar(
         SnackBar(
-          content: Text('Camera init failed: $e'),
+          content: Text(
+            userMessageForError(
+              e,
+              fallback: 'Failed to start camera. Please try again.',
+            ),
+          ),
           backgroundColor: Colors.red,
         ),
       );
@@ -165,7 +174,7 @@ class _ScannerScreenState extends State<ScannerScreen>
     });
   }
 
-  /// Capture a photo, run OCR, and look for a Hot Wheels ID.
+  /// Capture a photo, run OCR, and look for a die-cast model ID.
   Future<void> _captureAndScan() async {
     if (_isBusy || _cameraController == null || !_cameraController!.value.isInitialized) return;
     if (_cameraController!.value.isTakingPicture) return;
@@ -195,13 +204,23 @@ class _ScannerScreenState extends State<ScannerScreen>
       if (!mounted) return;
 
       if (found != null) {
+        _consecutiveMisses = 0;
         _nextScanAllowedAt = DateTime.now().add(_scanCooldownSuccess);
         setState(() => _lastDetected = found);
         if (widget.onDetected != null) {
           await _submitDetected(found);
         }
       } else {
-        _nextScanAllowedAt = DateTime.now().add(_scanCooldownNoMatch);
+        _consecutiveMisses += 1;
+        final missBackoffMs = (_scanCooldownNoMatch.inMilliseconds +
+                (_consecutiveMisses * 300))
+            .clamp(
+              _scanCooldownNoMatch.inMilliseconds,
+              _scanCooldownNoMatchMax.inMilliseconds,
+            );
+        _nextScanAllowedAt = DateTime.now().add(
+          Duration(milliseconds: missBackoffMs),
+        );
         setState(() {
           _scanAccepted = false;
           _scanNotFound = true;
@@ -209,10 +228,20 @@ class _ScannerScreenState extends State<ScannerScreen>
         });
       }
     } catch (e) {
+      _consecutiveMisses += 1;
       _nextScanAllowedAt = DateTime.now().add(_scanCooldownError);
       if (!mounted) return;
+      logError('scanner.capture', e);
       ScaffoldMessenger.of(context).showSnackBar(
-        SnackBar(content: Text('Scan error: $e'), backgroundColor: Colors.red),
+        SnackBar(
+          content: Text(
+            userMessageForError(
+              e,
+              fallback: 'Scan failed. Please try again.',
+            ),
+          ),
+          backgroundColor: Colors.red,
+        ),
       );
       setState(() => _statusText = 'Scan failed, try again');
     } finally {
@@ -258,8 +287,17 @@ class _ScannerScreenState extends State<ScannerScreen>
       }
     } catch (e) {
       if (!mounted) return;
+      logError('scanner.submitDetected', e);
       ScaffoldMessenger.of(context).showSnackBar(
-        SnackBar(content: Text('Process error: $e'), backgroundColor: Colors.red),
+        SnackBar(
+          content: Text(
+            userMessageForError(
+              e,
+              fallback: 'Could not process this scan. Please try again.',
+            ),
+          ),
+          backgroundColor: Colors.red,
+        ),
       );
     }
   }

lib/screens/about_screen.dart

@@ -106,7 +106,7 @@ class _AboutScreenState extends State<AboutScreen> {
           const SizedBox(height: 8),
           Center(
             child: Text(
-              'Track and manage your Hot Wheels collection.',
+              'Track and manage your die-cast car collection.',
               style: theme.textTheme.bodyMedium?.copyWith(
                 color: AppColors.textHint,
               ),

lib/screens/collections_screen.dart

@@ -4,6 +4,8 @@ import '../main.dart';
 import '../services/collection_service.dart';
 import '../services/main_collection_sync.dart';
 import '../theme/app_colors.dart';
+import '../utils/error_utils.dart';
+import '../utils/preferences_utils.dart';
 import 'garage_screen.dart';
 import 'manage_collection_screen.dart';
 
@@ -17,10 +19,10 @@ class CollectionsScreen extends StatefulWidget {
 
 class CollectionsScreenState extends State<CollectionsScreen>
   with WidgetsBindingObserver {
-  static const _activeCollectionPrefKey = 'active_collection_id';
-
   List<Collection> _collections = [];
   bool _isLoading = true;
+  bool _isLoadInFlight = false;
+  bool _reloadQueued = false;
   String? _error;
   String? _activeCollectionId;
   DateTime _lastLoadedAt = DateTime.fromMillisecondsSinceEpoch(0);
@@ -61,11 +63,20 @@ class CollectionsScreenState extends State<CollectionsScreen>
     }
   }
 
-  Future<void> _load() async {
+  Future<void> _load({bool showLoading = true}) async {
+    if (_isLoadInFlight) {
+      _reloadQueued = true;
+      return;
+    }
+
+    _isLoadInFlight = true;
+
+    if (showLoading) {
       setState(() {
         _isLoading = true;
         _error = null;
       });
+    }
 
     try {
       var list = await CollectionService.getMyCollections();
@@ -73,8 +84,13 @@ class CollectionsScreenState extends State<CollectionsScreen>
         await CollectionService.ensureDefaultCollection();
         list = await CollectionService.getMyCollections();
       }
+      final userId = supabase.auth.currentUser?.id;
+      if (userId == null) {
+        throw Exception('You must be signed in to load collections.');
+      }
+
       final prefs = await SharedPreferences.getInstance();
-      final persisted = prefs.getString(_activeCollectionPrefKey);
+      final persisted = await readActiveCollectionId(prefs, userId: userId);
 
       String? activeId = persisted;
       if (activeId == null && list.isNotEmpty) {
@@ -95,7 +111,11 @@ class CollectionsScreenState extends State<CollectionsScreen>
       });
 
       if (activeId != null) {
-        await prefs.setString(_activeCollectionPrefKey, activeId);
+        await writeActiveCollectionId(
+          prefs,
+          userId: userId,
+          collectionId: activeId,
+        );
         if (shouldNotifySync) {
           MainCollectionSync.notifyChanged();
         }
@@ -103,9 +123,19 @@ class CollectionsScreenState extends State<CollectionsScreen>
     } catch (e) {
       if (!mounted) return;
       setState(() {
-        _error = e.toString();
+        _error = userMessageForError(
+          e,
+          fallback: 'Failed to load collections. Please try again.',
+        );
         _isLoading = false;
       });
+      logError('collections.load', e);
+    } finally {
+      _isLoadInFlight = false;
+      if (_reloadQueued) {
+        _reloadQueued = false;
+        Future<void>.microtask(() => _load(showLoading: false));
+      }
     }
   }
 
@@ -137,7 +167,7 @@ class CollectionsScreenState extends State<CollectionsScreen>
                 maxLength: 50,
                 decoration: const InputDecoration(
                   labelText: 'Name',
-                  hintText: 'e.g. Hot Wheels, Matchbox…',
+                  hintText: 'e.g. Die-Cast Cars, Matchbox…',
                 ),
                 validator: (value) {
                   final trimmed = value?.trim() ?? '';
@@ -182,10 +212,13 @@ class CollectionsScreenState extends State<CollectionsScreen>
         name: nameCtrl.text.trim(),
         description: descCtrl.text.trim(),
       );
-      showGlobalSnackBar('Collection created!');
+      showGlobalSuccess('Collection created!');
       _load();
     } catch (e) {
-      showGlobalSnackBar('Failed: $e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Could not create collection. Please try again.',
+      );
     }
   }
 
@@ -210,12 +243,22 @@ class CollectionsScreenState extends State<CollectionsScreen>
   }
 
   Future<void> _setActiveCollection(String collectionId) async {
+    final userId = supabase.auth.currentUser?.id;
+    if (userId == null) {
+      showGlobalSnackBar('Please sign in again.', isError: true);
+      return;
+    }
+
     final prefs = await SharedPreferences.getInstance();
-    await prefs.setString(_activeCollectionPrefKey, collectionId);
+    await writeActiveCollectionId(
+      prefs,
+      userId: userId,
+      collectionId: collectionId,
+    );
     if (!mounted) return;
     setState(() => _activeCollectionId = collectionId);
     MainCollectionSync.notifyChanged();
-    showGlobalSnackBar('Main collection set for scanning.');
+    showGlobalInfo('Main collection set for scanning.');
   }
 
   @override

lib/screens/garage_screen.dart

@@ -7,9 +7,10 @@ import '../main.dart';
 import '../services/collection_service.dart';
 import '../services/storage_service.dart';
 import '../theme/app_colors.dart';
+import '../utils/error_utils.dart';
 import '../widgets/car_card.dart';
 
-/// The "My Garage" screen — shows a collection's cars in a grid.
+/// The "My Garage" screen — shows a collection's die-cast cars in a grid.
 class GarageScreen extends StatefulWidget {
   final String collectionId;
   final String collectionName;
@@ -108,21 +109,11 @@ class GarageScreenState extends State<GarageScreen> {
           .range(from, to);
 
       final rows = List<Map<String, dynamic>>.from(data);
-      final withSignedUrls = await Future.wait(
-        rows.map((row) async {
-          final path = row['user_image_url'] as String?;
-          final signed = await StorageService.createSignedUrl(path);
-          return {
-            ...row,
-            'signed_image_url': signed,
-          };
-        }),
-      );
 
       if (!mounted) return;
       setState(() {
-        _cars = reset ? withSignedUrls : [..._cars, ...withSignedUrls];
+        _cars = reset ? rows : [..._cars, ...rows];
-        _hasMore = withSignedUrls.length == _pageSize;
+        _hasMore = rows.length == _pageSize;
         if (_hasMore) _page += 1;
         _isLoading = false;
         _isLoadingMore = false;
@@ -130,10 +121,14 @@ class GarageScreenState extends State<GarageScreen> {
     } catch (e) {
       if (!mounted) return;
       setState(() {
-        _error = e.toString();
+        _error = userMessageForError(
+          e,
+          fallback: 'Failed to load cars. Please try again.',
+        );
         _isLoading = false;
         _isLoadingMore = false;
       });
+      logError('garage.loadCars', e);
     }
   }
 
@@ -329,14 +324,19 @@ class GarageScreenState extends State<GarageScreen> {
                       color: global?['color'] as String?,
                       isVerified: global?['is_verified'] == true,
                       imageUrl: car['signed_image_url'] as String?,
+                      imagePath: car['user_image_url'] as String?,
                       isSelected: _selectedIds.contains(carId),
                       addedAt: car['created_at'] != null
                           ? DateTime.tryParse(car['created_at'])
                           : null,
                       onImageError: () => _refreshSignedUrlForCar(carId),
-                      onTap: () => _selectionMode
+                      onTap: () {
-                          ? _toggleCarSelection(car)
+                        if (_selectionMode) {
-                          : _showCarDetails(car),
+                          _toggleCarSelection(car);
+                        } else {
+                          _showCarDetails(car);
+                        }
+                      },
                       onLongPress:
                           widget.isViewer ? null : () => _toggleCarSelection(car),
                     );
@@ -476,33 +476,110 @@ class GarageScreenState extends State<GarageScreen> {
       );
 
       if (confirmed != true || targetId == null) return;
+      final targetCollectionId = targetId!;
 
       if (isOwner) {
-        await supabase
-            .from('hotwheels')
-            .update({'collection_id': targetId})
-            .inFilter('id', _selectedIds.toList());
-      } else {
         final sourceCars = _cars
             .where((car) => _selectedIds.contains(car['id'] as int))
             .toList(growable: false);
 
+        final hwIds = sourceCars
+            .map((car) => car['hw_id'] as String)
+            .toSet()
+            .toList(growable: false);
+
+        final existing = await supabase
+            .from('hotwheels')
+            .select('hw_id')
+            .eq('collection_id', targetCollectionId)
+            .inFilter('hw_id', hwIds);
+
+        final existingHwIds = (existing as List)
+            .map((row) => row['hw_id'] as String)
+            .toSet();
+
+        final moveableIds = sourceCars
+            .where((car) => !existingHwIds.contains(car['hw_id'] as String))
+            .map((car) => car['id'] as int)
+            .toList(growable: false);
+
+        final skippedDuplicates = sourceCars.length - moveableIds.length;
+        if (moveableIds.isEmpty) {
+          showGlobalSnackBar(
+            'All selected cars are already in the target collection.',
+            isError: true,
+          );
+          return;
+        }
+
+        await supabase
+            .from('hotwheels')
+            .update({'collection_id': targetCollectionId})
+            .inFilter('id', moveableIds);
+
+        if (skippedDuplicates > 0) {
+          showGlobalSnackBar(
+            '$skippedDuplicates car(s) skipped because they already exist in target collection.',
+          );
+        }
+      } else {
+        final userId = supabase.auth.currentUser?.id;
+        if (userId == null) {
+          throw Exception('You must be signed in to copy cars.');
+        }
+
+        final sourceCars = _cars
+            .where((car) => _selectedIds.contains(car['id'] as int))
+            .toList(growable: false);
+
+        final hwIds = sourceCars
+            .map((car) => car['hw_id'] as String)
+            .toSet()
+            .toList(growable: false);
+
+        final existing = await supabase
+            .from('hotwheels')
+            .select('hw_id')
+          .eq('collection_id', targetCollectionId)
+            .inFilter('hw_id', hwIds);
+        final existingHwIds = (existing as List)
+            .map((row) => row['hw_id'] as String)
+            .toSet();
+
         final insertRows = sourceCars.map((car) {
           final notes = car['notes'] as String?;
           final imagePath = car['user_image_url'] as String?;
           return <String, dynamic>{
             'hw_id': car['hw_id'] as String,
-            'user_id': supabase.auth.currentUser!.id,
+            'user_id': userId,
-            'collection_id': targetId,
+            'collection_id': targetCollectionId,
             if (notes != null && notes.trim().isNotEmpty) 'notes': notes,
             if (imagePath != null && imagePath.isNotEmpty)
               'user_image_url': imagePath,
           };
-        }).toList(growable: false);
+        }).where((row) => !existingHwIds.contains(row['hw_id'] as String)).toList(
+              growable: false,
+            );
+
+        final skippedDuplicates = sourceCars.length - insertRows.length;
+
+        if (insertRows.isEmpty) {
+          showGlobalSnackBar(
+            'All selected cars are already in the target collection.',
+            isError: true,
+          );
+          return;
+        }
 
         if (insertRows.isNotEmpty) {
           await supabase.from('hotwheels').insert(insertRows);
         }
+
+        if (skippedDuplicates > 0) {
+          showGlobalSnackBar(
+            '$skippedDuplicates car(s) skipped because they already exist in target collection.',
+          );
+        }
       }
 
       if (!mounted) return;
@@ -514,9 +591,11 @@ class GarageScreenState extends State<GarageScreen> {
       _toggleSelectionMode(false);
       await _loadCars(reset: true);
     } catch (e) {
-      showGlobalSnackBar(
+      showGlobalError(
-        widget.isOwner ? 'Failed to move cars: $e' : 'Failed to copy cars: $e',
+        e,
-        isError: true,
+        fallback: widget.isOwner
+            ? 'Failed to move cars. Please try again.'
+            : 'Failed to copy cars. Please try again.',
       );
     }
   }
@@ -545,7 +624,7 @@ class GarageScreenState extends State<GarageScreen> {
     }
   }
 
-  void _showCarDetails(Map<String, dynamic> car) {
+  Future<void> _showCarDetails(Map<String, dynamic> car) async {
     if (_selectionMode) {
       _toggleCarSelection(car);
       return;
@@ -559,7 +638,24 @@ class GarageScreenState extends State<GarageScreen> {
     final verified = global?['is_verified'] == true;
     final confirmations = (global?['confirmation_count'] as num?)?.toInt() ?? 0;
     final notes = car['notes'] as String?;
-    final imageUrl = car['signed_image_url'] as String?;
+    String? imageUrl = car['signed_image_url'] as String?;
+    if (imageUrl == null || imageUrl.isEmpty) {
+      final path = car['user_image_url'] as String?;
+      final signed = await StorageService.createSignedUrl(path);
+      if (!mounted) return;
+      if (signed != null && signed.isNotEmpty) {
+        imageUrl = signed;
+        final index = _cars.indexWhere((c) => c['id'] == car['id']);
+        if (index != -1) {
+          setState(() {
+            _cars[index] = {
+              ..._cars[index],
+              'signed_image_url': signed,
+            };
+          });
+        }
+      }
+    }
 
     showModalBottomSheet(
       context: context,
@@ -817,7 +913,7 @@ class GarageScreenState extends State<GarageScreen> {
     );
     if (xFile == null) return;
 
-    showGlobalSnackBar('Uploading photo…');
+    showGlobalInfo('Uploading photo…');
 
     final oldPath = car['user_image_url'] as String?;
     String newPath;
@@ -828,9 +924,9 @@ class GarageScreenState extends State<GarageScreen> {
         oldPath: oldPath,
       );
     } catch (e) {
-      showGlobalSnackBar(
+      showGlobalError(
-        'Failed to upload photo. Please try a smaller/clearer image. ($e)',
+        e,
-        isError: true,
+        fallback: 'Failed to upload photo. Please try a smaller image.',
       );
       return;
     }
@@ -841,11 +937,14 @@ class GarageScreenState extends State<GarageScreen> {
           .update({'user_image_url': newPath})
           .eq('id', car['id']);
 
-      showGlobalSnackBar('Photo updated!');
+      showGlobalSuccess('Photo updated!');
       if (sheetContext.mounted) Navigator.pop(sheetContext);
       _loadCars(reset: true); // refresh grid
     } catch (e) {
-      showGlobalSnackBar('Failed to save: $e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Failed to save photo. Please try again.',
+      );
     }
   }
 
@@ -869,11 +968,14 @@ class GarageScreenState extends State<GarageScreen> {
           .update(updated)
           .eq('id', car['id']);
 
-      showGlobalSnackBar('Car updated!');
+      showGlobalSuccess('Car updated!');
       if (sheetContext.mounted) Navigator.pop(sheetContext);
       _loadCars(reset: true);
     } catch (e) {
-      showGlobalSnackBar('Failed to update: $e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Failed to update car. Please try again.',
+      );
     }
   }
 
@@ -890,7 +992,7 @@ class GarageScreenState extends State<GarageScreen> {
           .maybeSingle();
 
       if (existingVote != null) {
-        showGlobalSnackBar('You already confirmed this catalog entry.');
+        showGlobalInfo('You already confirmed this catalog entry.');
         return;
       }
 
@@ -899,11 +1001,14 @@ class GarageScreenState extends State<GarageScreen> {
         'user_id': user.id,
       });
 
-      showGlobalSnackBar('Thanks! Your validation vote was recorded.');
+      showGlobalSuccess('Thanks! Your validation vote was recorded.');
       if (sheetContext.mounted) Navigator.pop(sheetContext);
       _loadCars(reset: true);
     } catch (e) {
-      showGlobalSnackBar('Failed to submit validation vote: $e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Failed to submit validation vote. Please try again.',
+      );
     }
   }
 
@@ -939,7 +1044,7 @@ class GarageScreenState extends State<GarageScreen> {
           .maybeSingle();
 
       if (existingOpen != null) {
-        showGlobalSnackBar('You already have an open report for this car.');
+        showGlobalInfo('You already have an open report for this car.');
         return;
       }
 
@@ -951,9 +1056,12 @@ class GarageScreenState extends State<GarageScreen> {
         'note': payload.note,
       });
 
-      showGlobalSnackBar('Thanks for reporting. We will review this entry.');
+      showGlobalSuccess('Thanks for reporting. We will review this entry.');
     } catch (e) {
-      showGlobalSnackBar('Failed to submit report: $e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Failed to submit report. Please try again.',
+      );
     }
   }
 
@@ -1023,16 +1131,51 @@ class GarageScreenState extends State<GarageScreen> {
       if (targetId == null) return;
 
       if (widget.isOwner) {
+        final existing = await supabase
+            .from('hotwheels')
+            .select('id')
+            .eq('collection_id', targetId)
+            .eq('hw_id', car['hw_id'])
+            .maybeSingle();
+
+        if (existing != null) {
+          showGlobalSnackBar(
+            '${car['hw_id']} is already in the target collection.',
+            isError: true,
+          );
+          return;
+        }
+
         await supabase
             .from('hotwheels')
             .update({'collection_id': targetId})
             .eq('id', car['id']);
       } else {
+        final userId = supabase.auth.currentUser?.id;
+        if (userId == null) {
+          throw Exception('You must be signed in to copy cars.');
+        }
+
+        final existing = await supabase
+            .from('hotwheels')
+            .select('id')
+            .eq('collection_id', targetId)
+            .eq('hw_id', car['hw_id'])
+            .maybeSingle();
+
+        if (existing != null) {
+          showGlobalSnackBar(
+            '${car['hw_id']} is already in the target collection.',
+            isError: true,
+          );
+          return;
+        }
+
         final notes = car['notes'] as String?;
         final imagePath = car['user_image_url'] as String?;
         await supabase.from('hotwheels').insert({
           'hw_id': car['hw_id'] as String,
-          'user_id': supabase.auth.currentUser!.id,
+          'user_id': userId,
           'collection_id': targetId,
           if (notes != null && notes.trim().isNotEmpty) 'notes': notes,
           if (imagePath != null && imagePath.isNotEmpty)
@@ -1042,14 +1185,16 @@ class GarageScreenState extends State<GarageScreen> {
 
       if (!mounted) return;
       if (sheetContext.mounted) Navigator.pop(sheetContext);
-      showGlobalSnackBar(widget.isOwner
+        showGlobalSuccess(widget.isOwner
           ? '${car['hw_id']} moved to another collection.'
           : '${car['hw_id']} copied to another collection.');
       await _loadCars(reset: true);
     } catch (e) {
-      showGlobalSnackBar(
+      showGlobalError(
-        widget.isOwner ? 'Failed to move car: $e' : 'Failed to copy car: $e',
+        e,
-        isError: true,
+        fallback: widget.isOwner
+            ? 'Failed to move car. Please try again.'
+            : 'Failed to copy car. Please try again.',
       );
     }
   }
@@ -1097,10 +1242,13 @@ class GarageScreenState extends State<GarageScreen> {
       if (sheetContext.mounted) {
         Navigator.pop(sheetContext); // close bottom sheet
       }
-      showGlobalSnackBar('${car['hw_id']} removed from your garage.');
+      showGlobalSuccess('${car['hw_id']} removed from your garage.');
       _loadCars(reset: true);
     } catch (e) {
-      showGlobalSnackBar('Failed to remove: $e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Failed to remove car. Please try again.',
+      );
     }
   }
 }
@@ -1200,7 +1348,7 @@ class _EmptyGarage extends StatelessWidget {
             Text(
               hasSearch
                   ? 'Try a different search term'
-                  : 'Scan your first Hot Wheels car to get started!',
+                  : 'Scan your first die-cast car to get started!',
               textAlign: TextAlign.center,
               style: const TextStyle(color: AppColors.textHint),
             ),

lib/screens/login_screen.dart

@@ -78,7 +78,7 @@ class _LoginScreenState extends State<LoginScreen>
         email,
         redirectTo: 'hwcollector://login/recovery',
       );
-      showGlobalSnackBar('Password reset email sent! Check your inbox.');
+      showGlobalSuccess('Password reset email sent! Check your inbox.');
     } on AuthException catch (e) {
       showGlobalSnackBar(e.message, isError: true);
     }

lib/screens/manage_collection_screen.dart

@@ -40,7 +40,10 @@ class _ManageCollectionScreenState extends State<ManageCollectionScreen> {
     } catch (e) {
       if (!mounted) return;
       setState(() => _isLoading = false);
-      showGlobalSnackBar('Failed to load members: $e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Failed to load members. Please try again.',
+      );
     }
   }
 
@@ -122,9 +125,12 @@ class _ManageCollectionScreenState extends State<ManageCollectionScreen> {
           memberCount: _collection.memberCount,
         );
       });
-      showGlobalSnackBar('Collection renamed!');
+      showGlobalSuccess('Collection renamed!');
     } catch (e) {
-      showGlobalSnackBar('Failed: $e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Could not rename collection. Please try again.',
+      );
     }
   }
 
@@ -238,12 +244,15 @@ class _ManageCollectionScreenState extends State<ManageCollectionScreen> {
         email: email,
         role: inviteRole,
       );
-      showGlobalSnackBar(
+      showGlobalSuccess(
         inviteRole == 'viewer' ? 'Viewer invited!' : 'Member invited!',
       );
       await _loadMembers();
     } catch (e) {
-      showGlobalSnackBar('$e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Could not send invitation. Please try again.',
+      );
     } finally {
       if (mounted) setState(() => _isInviting = false);
     }
@@ -277,10 +286,13 @@ class _ManageCollectionScreenState extends State<ManageCollectionScreen> {
         collectionId: _collection.id,
         memberUserId: member.userId,
       );
-      showGlobalSnackBar('Member removed.');
+      showGlobalSuccess('Member removed.');
       await _loadMembers();
     } catch (e) {
-      showGlobalSnackBar('Failed: $e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Could not remove member. Please try again.',
+      );
     }
   }
 
@@ -310,10 +322,13 @@ class _ManageCollectionScreenState extends State<ManageCollectionScreen> {
 
     try {
       await CollectionService.leave(_collection.id);
-      showGlobalSnackBar('Left "${_collection.name}".');
+      showGlobalSuccess('Left "${_collection.name}".');
       if (mounted) Navigator.pop(context);
     } catch (e) {
-      showGlobalSnackBar('Failed: $e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Could not leave collection. Please try again.',
+      );
     }
   }
 
@@ -343,10 +358,13 @@ class _ManageCollectionScreenState extends State<ManageCollectionScreen> {
 
     try {
       await CollectionService.delete(_collection.id);
-      showGlobalSnackBar('Collection deleted.');
+      showGlobalSuccess('Collection deleted.');
       if (mounted) Navigator.pop(context);
     } catch (e) {
-      showGlobalSnackBar('Failed: $e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Could not delete collection. Please try again.',
+      );
     }
   }
 

lib/screens/my_reports_screen.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import '../main.dart';
 import '../theme/app_colors.dart';
+import '../utils/error_utils.dart';
 import '../utils/reporting_utils.dart';
 
 class MyReportsScreen extends StatefulWidget {
@@ -23,7 +24,15 @@ class _MyReportsScreenState extends State<MyReportsScreen> {
 
   Future<void> _loadReports() async {
     final user = supabase.auth.currentUser;
-    if (user == null) return;
+    if (user == null) {
+      if (!mounted) return;
+      setState(() {
+        _reports = [];
+        _error = 'Please sign in to view reports.';
+        _isLoading = false;
+      });
+      return;
+    }
 
     setState(() {
       _isLoading = true;
@@ -45,9 +54,13 @@ class _MyReportsScreenState extends State<MyReportsScreen> {
     } catch (e) {
       if (!mounted) return;
       setState(() {
-        _error = e.toString();
+        _error = userMessageForError(
+          e,
+          fallback: 'Failed to load reports. Please try again.',
+        );
         _isLoading = false;
       });
+      logError('reports.load', e);
     }
   }
 

lib/screens/profile_screen.dart

@@ -208,7 +208,7 @@ class ProfileScreen extends StatelessWidget {
                   UserAttributes(password: pw),
                 );
                 if (context.mounted) Navigator.pop(context);
-                showGlobalSnackBar('Password updated!');
+                showGlobalSuccess('Password updated!');
               } on AuthException catch (e) {
                 showGlobalSnackBar(e.message, isError: true);
               }

lib/screens/scan_tab.dart

@@ -5,6 +5,7 @@ import '../scanner_screen.dart';
 import '../services/collection_service.dart';
 import '../services/main_collection_sync.dart';
 import '../theme/app_colors.dart';
+import '../utils/preferences_utils.dart';
 
 class ScanTab extends StatefulWidget {
   const ScanTab({super.key});
@@ -14,7 +15,6 @@ class ScanTab extends StatefulWidget {
 }
 
 class ScanTabState extends State<ScanTab> {
-  static const _activeCollectionPrefKey = 'active_collection_id';
   static const _duplicateCooldown = Duration(seconds: 2);
 
   bool _isBusy = false;
@@ -50,8 +50,13 @@ class ScanTabState extends State<ScanTab> {
   Future<void> _loadCollections() async {
     try {
       final list = await CollectionService.getMyCollections();
+      final userId = supabase.auth.currentUser?.id;
+      if (userId == null) {
+        throw Exception('You must be signed in to load collections.');
+      }
+
       final prefs = await SharedPreferences.getInstance();
-      final persistedId = prefs.getString(_activeCollectionPrefKey);
+      final persistedId = await readActiveCollectionId(prefs, userId: userId);
 
       Collection? selected;
       if (persistedId != null) {
@@ -71,12 +76,19 @@ class ScanTabState extends State<ScanTab> {
       });
 
       if (selected != null) {
-        await prefs.setString(_activeCollectionPrefKey, selected.id);
+        await writeActiveCollectionId(
+          prefs,
+          userId: userId,
+          collectionId: selected.id,
+        );
       }
     } catch (e) {
       if (!mounted) return;
       setState(() => _loadingCollections = false);
-      showGlobalSnackBar('Failed to load collections: $e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Failed to load collections. Please try again.',
+      );
     }
   }
 
@@ -104,7 +116,7 @@ class ScanTabState extends State<ScanTab> {
               ),
               const SizedBox(height: 28),
               const Text(
-                'Scan a Hot Wheels Car',
+                'Scan a Die-Cast Car',
                 style: TextStyle(fontSize: 22, fontWeight: FontWeight.w700),
               ),
               const SizedBox(height: 10),
@@ -379,7 +391,7 @@ class ScanTabState extends State<ScanTab> {
           await _addToCollection(collection.id, hwId);
           await _ensureValidationVote(hwId);
           if (!mounted) return false;
-          showGlobalSnackBar('$hwId added to "${collection.name}"! 🎉');
+          showGlobalSuccess('$hwId added to "${collection.name}"! 🎉');
         }
       } else {
         final discovery = await showModalBottomSheet<_NewDiscoveryData>(
@@ -403,13 +415,16 @@ class ScanTabState extends State<ScanTab> {
           );
           await _addToCollection(collection.id, hwId, notes: discovery.notes);
           if (!mounted) return false;
-          showGlobalSnackBar('$hwId added to "${collection.name}"! 🎉');
+          showGlobalSuccess('$hwId added to "${collection.name}"! 🎉');
         }
       }
       return true;
     } catch (e) {
       if (mounted) setState(() => _isBusy = false);
-      showGlobalSnackBar('DB error: $e', isError: true);
+      showGlobalError(
+        e,
+        fallback: 'Could not save this car right now. Please try again.',
+      );
       return true;
     }
   }
@@ -419,9 +434,14 @@ class ScanTabState extends State<ScanTab> {
     String hwId, {
     String? notes,
   }) async {
+    final userId = supabase.auth.currentUser?.id;
+    if (userId == null) {
+      throw Exception('You must be signed in to add cars.');
+    }
+
     await supabase.from('hotwheels').insert({
       'hw_id': hwId,
-      'user_id': supabase.auth.currentUser!.id,
+      'user_id': userId,
       'collection_id': collectionId,
       if (notes != null && notes.trim().isNotEmpty) 'notes': notes.trim(),
     });
@@ -433,6 +453,11 @@ class ScanTabState extends State<ScanTab> {
     String? series,
     int? year,
   }) async {
+    final userId = supabase.auth.currentUser?.id;
+    if (userId == null) {
+      throw Exception('You must be signed in to create catalog entries.');
+    }
+
     final cleanedSeries = series?.trim();
     final payload = <String, dynamic>{
       'hw_id': hwId,
@@ -445,12 +470,15 @@ class ScanTabState extends State<ScanTab> {
 
     await supabase.from('car_votes').insert({
       'hw_id': hwId,
-      'user_id': supabase.auth.currentUser!.id,
+      'user_id': userId,
     });
   }
 
   Future<void> _ensureValidationVote(String hwId) async {
-    final userId = supabase.auth.currentUser!.id;
+    final userId = supabase.auth.currentUser?.id;
+    if (userId == null) {
+      throw Exception('You must be signed in to validate entries.');
+    }
     final existingVote = await supabase
         .from('car_votes')
         .select('id')

lib/services/collection_service.dart

@@ -53,6 +53,14 @@ class CollectionMember {
 class CollectionService {
   CollectionService._();
 
+  static String _requireUserId() {
+    final userId = supabase.auth.currentUser?.id;
+    if (userId == null) {
+      throw Exception('You must be signed in to perform this action.');
+    }
+    return userId;
+  }
+
   /// Ensures the current user has at least one collection membership.
   /// Creates a default collection on first login.
   static Future<String?> ensureDefaultCollection() async {
@@ -80,7 +88,7 @@ class CollectionService {
   /// Fetch all collections the current user is a member of,
   /// including item count and member count.
   static Future<List<Collection>> getMyCollections() async {
-    final userId = supabase.auth.currentUser!.id;
+    final userId = _requireUserId();
 
     // Get memberships with collection data.
     final memberships = await supabase
@@ -113,11 +121,9 @@ class CollectionService {
         });
         memberCounts[collectionId] = (rows as List).length;
       } catch (_) {
-        // Keep fallback below when RPC fails.
       }
     }));
 
-    // Fallback member count for collections where RPC did not return data.
     final unresolvedIds = collectionIdList
         .where((id) => !memberCounts.containsKey(id))
         .toList(growable: false);
@@ -249,7 +255,7 @@ class CollectionService {
     required String name,
     String? description,
   }) async {
-    final userId = supabase.auth.currentUser!.id;
+    final userId = _requireUserId();
 
     final row = await supabase
         .from('collections')
@@ -287,7 +293,7 @@ class CollectionService {
     required String name,
     String? description,
   }) async {
-    final userId = supabase.auth.currentUser!.id;
+    final userId = _requireUserId();
 
     final collection = await supabase
         .from('collections')
@@ -311,7 +317,7 @@ class CollectionService {
 
   /// Delete a collection. Owner only. Cascade deletes members & items.
   static Future<void> delete(String collectionId) async {
-    final userId = supabase.auth.currentUser!.id;
+    final userId = _requireUserId();
 
     final collection = await supabase
         .from('collections')
@@ -362,7 +368,7 @@ class CollectionService {
       throw Exception('Unsupported role "$role".');
     }
 
-    final currentUserId = supabase.auth.currentUser!.id;
+    final currentUserId = _requireUserId();
 
     final collection = await supabase
         .from('collections')
@@ -428,7 +434,7 @@ class CollectionService {
     required String collectionId,
     required String memberUserId,
   }) async {
-    final currentUserId = supabase.auth.currentUser!.id;
+    final currentUserId = _requireUserId();
 
     final collection = await supabase
         .from('collections')
@@ -501,7 +507,7 @@ class CollectionService {
 
   /// Leave a collection (for non-owners).
   static Future<void> leave(String collectionId) async {
-    final userId = supabase.auth.currentUser!.id;
+    final userId = _requireUserId();
 
     final membership = await supabase
         .from('collection_members')

lib/services/storage_service.dart

@@ -7,7 +7,7 @@ import '../main.dart';
 /// Handles uploading / deleting car images in Supabase Storage.
 ///
 /// Bucket: `car-images` (private)
-/// Path:   `{auth.uid()}/{hotwheels.id}.jpg`
+/// Path:   `{auth.uid()}/{entry.id}.jpg`
 class StorageService {
   StorageService._();
 
@@ -20,7 +20,7 @@ class StorageService {
   static const _maxSignedUrlCacheEntries = 500;
   static final Map<String, _SignedUrlCacheEntry> _signedUrlCache = {};
 
-  /// Upload a car image for a specific hotwheels entry.
+  /// Upload a car image for a specific garage entry.
   /// Returns the storage path on success (e.g. `uid/123.jpg`).
   static Future<String> uploadCarImage({
     required File file,
@@ -31,7 +31,11 @@ class StorageService {
       await deleteCarImage(oldPath);
     }
 
-    final userId = supabase.auth.currentUser!.id;
+    final user = supabase.auth.currentUser;
+    if (user == null) {
+      throw Exception('You must be signed in to upload images.');
+    }
+    final userId = user.id;
     final path = '$userId/$entryId.jpg';
     final compressed = await _compressImage(file);
 

lib/utils/error_utils.dart

@@ -0,0 +1,37 @@
+import 'package:flutter/foundation.dart';
+import 'package:supabase_flutter/supabase_flutter.dart';
+
+String userMessageForError(
+  Object error, {
+  String fallback = 'Something went wrong. Please try again.',
+}) {
+  if (error is AuthException) {
+    return error.message;
+  }
+
+  final raw = error.toString();
+  final normalized = raw.toLowerCase();
+
+  if (normalized.contains('socket') ||
+      normalized.contains('network') ||
+      normalized.contains('timeout')) {
+    return 'Network issue. Please check your connection and try again.';
+  }
+
+  if (normalized.contains('permission') || normalized.contains('not allowed')) {
+    return 'You do not have permission for this action.';
+  }
+
+  if (normalized.contains('signed in')) {
+    return 'Please sign in again and retry.';
+  }
+
+  return fallback;
+}
+
+void logError(String scope, Object error, [StackTrace? stackTrace]) {
+  debugPrint('[$scope] $error');
+  if (stackTrace != null) {
+    debugPrint('$stackTrace');
+  }
+}

lib/utils/preferences_utils.dart

@@ -0,0 +1,43 @@
+import 'package:shared_preferences/shared_preferences.dart';
+
+const _legacyActiveCollectionPrefKey = 'active_collection_id';
+
+String activeCollectionPrefKeyForUser(String userId) {
+  return 'active_collection_id_$userId';
+}
+
+Future<String?> readActiveCollectionId(
+  SharedPreferences prefs, {
+  required String userId,
+}) async {
+  final scopedKey = activeCollectionPrefKeyForUser(userId);
+  final scopedValue = prefs.getString(scopedKey);
+  if (scopedValue != null && scopedValue.isNotEmpty) {
+    return scopedValue;
+  }
+
+  final legacyValue = prefs.getString(_legacyActiveCollectionPrefKey);
+  if (legacyValue == null || legacyValue.isEmpty) {
+    return null;
+  }
+
+  await prefs.setString(scopedKey, legacyValue);
+  await prefs.remove(_legacyActiveCollectionPrefKey);
+  return legacyValue;
+}
+
+Future<void> writeActiveCollectionId(
+  SharedPreferences prefs, {
+  required String userId,
+  required String collectionId,
+}) {
+  return prefs.setString(activeCollectionPrefKeyForUser(userId), collectionId);
+}
+
+Future<void> clearActiveCollectionId(
+  SharedPreferences prefs, {
+  required String userId,
+}) async {
+  await prefs.remove(activeCollectionPrefKeyForUser(userId));
+  await prefs.remove(_legacyActiveCollectionPrefKey);
+}

lib/widgets/car_card.dart

@@ -1,8 +1,9 @@
 import 'package:flutter/material.dart';
 import 'package:cached_network_image/cached_network_image.dart';
+import '../services/storage_service.dart';
 import '../theme/app_colors.dart';
 
-/// A styled card for displaying a single Hot Wheels car in the garage.
+/// A styled card for displaying a single die-cast car in the garage.
 class CarCard extends StatelessWidget {
   final String hwId;
   final String? name;
@@ -10,6 +11,7 @@ class CarCard extends StatelessWidget {
   final int? year;
   final String? color;
   final String? imageUrl;
+  final String? imagePath;
   final bool isVerified;
   final DateTime? addedAt;
   final VoidCallback? onTap;
@@ -25,6 +27,7 @@ class CarCard extends StatelessWidget {
     this.year,
     this.color,
     this.imageUrl,
+    this.imagePath,
     this.isVerified = false,
     this.addedAt,
     this.onTap,
@@ -37,6 +40,9 @@ class CarCard extends StatelessWidget {
   Widget build(BuildContext context) {
     final theme = Theme.of(context);
     final isDark = theme.brightness == Brightness.dark;
+    final resolvedImageUrl = imageUrl;
+    final hasResolvedUrl = resolvedImageUrl != null && resolvedImageUrl.isNotEmpty;
+    final hasImagePath = imagePath != null && imagePath!.isNotEmpty;
 
     return Card(
       clipBehavior: Clip.antiAlias,
@@ -66,9 +72,9 @@ class CarCard extends StatelessWidget {
                         )
                       : AppColors.brandGradientSoft,
                 ),
-                child: imageUrl != null && imageUrl!.isNotEmpty
+                child: hasResolvedUrl
                     ? CachedNetworkImage(
-                        imageUrl: imageUrl!,
+                        imageUrl: resolvedImageUrl,
                         fit: BoxFit.cover,
                         fadeInDuration: Duration.zero,
                         fadeOutDuration: Duration.zero,
@@ -77,6 +83,26 @@ class CarCard extends StatelessWidget {
                           return _PlaceholderIcon(isDark: isDark);
                         },
                       )
+                    : hasImagePath
+                        ? FutureBuilder<String?>(
+                            future: StorageService.createSignedUrl(imagePath),
+                            builder: (context, snapshot) {
+                              final signedUrl = snapshot.data;
+                              if (signedUrl == null || signedUrl.isEmpty) {
+                                return _PlaceholderIcon(isDark: isDark);
+                              }
+                              return CachedNetworkImage(
+                                imageUrl: signedUrl,
+                                fit: BoxFit.cover,
+                                fadeInDuration: Duration.zero,
+                                fadeOutDuration: Duration.zero,
+                                errorWidget: (context, url, error) {
+                                  onImageError?.call();
+                                  return _PlaceholderIcon(isDark: isDark);
+                                },
+                              );
+                            },
+                          )
                         : _PlaceholderIcon(isDark: isDark),
               ),
             ),