feat: add C# and Dart language support

commands/flutter-build.md

@@ -0,0 +1,164 @@
+---
+description: Fix Dart analyzer errors and Flutter build failures incrementally. Invokes the dart-build-resolver agent for minimal, surgical fixes.
+---
+
+# Flutter Build and Fix
+
+This command invokes the **dart-build-resolver** agent to incrementally fix Dart/Flutter build errors with minimal changes.
+
+## What This Command Does
+
+1. **Run Diagnostics**: Execute `flutter analyze`, `flutter pub get`
+2. **Parse Errors**: Group by file and sort by severity
+3. **Fix Incrementally**: One error at a time
+4. **Verify Each Fix**: Re-run analysis after each change
+5. **Report Summary**: Show what was fixed and what remains
+
+## When to Use
+
+Use `/flutter-build` when:
+- `flutter analyze` reports errors
+- `flutter build` fails for any platform
+- `dart pub get` / `flutter pub get` fails with version conflicts
+- `build_runner` fails to generate code
+- After pulling changes that break the build
+
+## Diagnostic Commands Run
+
+```bash
+# Analysis
+flutter analyze 2>&1
+
+# Dependencies
+flutter pub get 2>&1
+
+# Code generation (if project uses build_runner)
+dart run build_runner build --delete-conflicting-outputs 2>&1
+
+# Platform builds
+flutter build apk 2>&1
+flutter build web 2>&1
+```
+
+## Example Session
+
+````text
+User: /flutter-build
+
+Agent:
+# Flutter Build Resolution
+
+## Initial Diagnostics
+
+```
+$ flutter analyze
+Analyzing project...
+
+  error • lib/features/user/data/user_repository_impl.dart:34:16 •
+    A value of type 'String?' can't be assigned to a variable of type 'String'. •
+    invalid_assignment
+
+  error • lib/features/cart/presentation/cart_page.dart:58:5 •
+    The method 'add' isn't defined for the type 'List<Item>'.
+    Try correcting the name to the name of an existing method, or defining a method named 'add'. •
+    undefined_method
+
+2 errors found.
+```
+
+## Fix 1: Null Safety
+
+File: lib/features/user/data/user_repository_impl.dart:34
+Error: A value of type 'String?' can't be assigned to type 'String'
+
+Changed:
+```dart
+final id = response.id;
+```
+To:
+```dart
+final id = response.id ?? '';
+```
+
+```
+$ flutter analyze
+1 error found.
+```
+
+## Fix 2: Immutable List
+
+File: lib/features/cart/presentation/cart_page.dart:58
+Error: The method 'add' isn't defined for the type 'List<Item>'
+Cause: State holds an unmodifiable list; mutation goes through Cubit
+
+Changed:
+```dart
+state.items.add(item);
+```
+To:
+```dart
+context.read<CartCubit>().addItem(item);
+// Note: Cubit exposes named methods (addItem, removeItem);
+// .add(event) is the BLoC event API — don't mix them.
+```
+
+```
+$ flutter analyze
+No issues found!
+```
+
+## Final Verification
+
+```
+$ flutter test
+All tests passed.
+```
+
+## Summary
+
+| Metric | Count |
+|--------|-------|
+| Analysis errors fixed | 2 |
+| Files modified | 2 |
+| Remaining issues | 0 |
+
+Build Status: PASS ✓
+````
+
+## Common Errors Fixed
+
+| Error | Typical Fix |
+|-------|-------------|
+| `A value of type 'X?' can't be assigned to 'X'` | Add `?? default` or null guard |
+| `The name 'X' isn't defined` | Add import or fix typo |
+| `Non-nullable instance field must be initialized` | Add initializer or `late` |
+| `Version solving failed` | Adjust version constraints in pubspec.yaml |
+| `Missing concrete implementation of 'X'` | Implement missing interface method |
+| `build_runner: Part of X expected` | Delete stale `.g.dart` and rebuild |
+
+## Fix Strategy
+
+1. **Analysis errors first** — code must be error-free
+2. **Warning triage second** — fix warnings that could cause runtime bugs
+3. **pub conflicts third** — fix dependency resolution
+4. **One fix at a time** — verify each change
+5. **Minimal changes** — don't refactor, just fix
+
+## Stop Conditions
+
+The agent will stop and report if:
+- Same error persists after 3 attempts
+- Fix introduces more errors
+- Requires architectural changes
+- Package upgrade conflicts need user decision
+
+## Related Commands
+
+- `/flutter-test` — Run tests after build succeeds
+- `/flutter-review` — Review code quality
+- `/verify` — Full verification loop
+
+## Related
+
+- Agent: `agents/dart-build-resolver.md`
+- Skill: `skills/flutter-dart-code-review/`