feat: add Kotlin, Android, and KMP rules, agent, skills, and command

rules/kotlin/patterns.md

@@ -0,0 +1,139 @@
+---
+paths:
+  - "**/*.kt"
+  - "**/*.kts"
+---
+# Kotlin Patterns
+
+> This file extends [common/patterns.md](../common/patterns.md) with Kotlin and Android/KMP specific content.
+
+## Dependency Injection
+
+Prefer constructor injection. Use Koin (KMP) or Hilt (Android-only):
+
+```kotlin
+// Koin — declare modules
+val dataModule = module {
+    single<ItemRepository> { ItemRepositoryImpl(get(), get()) }
+    factory { GetItemsUseCase(get()) }
+    viewModelOf(::ItemListViewModel)
+}
+
+// Hilt — annotations
+@HiltViewModel
+class ItemListViewModel @Inject constructor(
+    private val getItems: GetItemsUseCase
+) : ViewModel()
+```
+
+## ViewModel Pattern
+
+Single state object, event sink, one-way data flow:
+
+```kotlin
+data class ScreenState(
+    val items: List<Item> = emptyList(),
+    val isLoading: Boolean = false
+)
+
+class ScreenViewModel(private val useCase: GetItemsUseCase) : ViewModel() {
+    private val _state = MutableStateFlow(ScreenState())
+    val state = _state.asStateFlow()
+
+    fun onEvent(event: ScreenEvent) {
+        when (event) {
+            is ScreenEvent.Load -> load()
+            is ScreenEvent.Delete -> delete(event.id)
+        }
+    }
+}
+```
+
+## Repository Pattern
+
+- `suspend` functions return `Result<T>` or custom error type
+- `Flow` for reactive streams
+- Coordinate local + remote data sources
+
+```kotlin
+interface ItemRepository {
+    suspend fun getById(id: String): Result<Item>
+    fun observeAll(): Flow<List<Item>>
+}
+```
+
+## UseCase Pattern
+
+Single responsibility, `operator fun invoke`:
+
+```kotlin
+class GetItemsUseCase(private val repository: ItemRepository) {
+    suspend operator fun invoke(filter: Filter): Result<List<Item>> {
+        return repository.getAll(filter)
+    }
+}
+```
+
+## expect/actual (KMP)
+
+Use for platform-specific implementations:
+
+```kotlin
+// commonMain
+expect fun platformName(): String
+expect class SecureStorage {
+    fun save(key: String, value: String)
+    fun get(key: String): String?
+}
+
+// androidMain
+actual fun platformName(): String = "Android"
+actual class SecureStorage {
+    actual fun save(key: String, value: String) { /* EncryptedSharedPreferences */ }
+    actual fun get(key: String): String? { /* ... */ }
+}
+
+// iosMain
+actual fun platformName(): String = "iOS"
+actual class SecureStorage {
+    actual fun save(key: String, value: String) { /* Keychain */ }
+    actual fun get(key: String): String? { /* ... */ }
+}
+```
+
+## Coroutine Patterns
+
+- Use `viewModelScope` in ViewModels, `coroutineScope` for structured child work
+- Use `stateIn(WhileSubscribed(5_000))` for StateFlow from cold Flows
+- Use `supervisorScope` when child failures should be independent
+
+## Builder Pattern with DSL
+
+```kotlin
+class HttpClientConfig {
+    var baseUrl: String = ""
+    var timeout: Long = 30_000
+    private val interceptors = mutableListOf<Interceptor>()
+
+    fun interceptor(block: () -> Interceptor) {
+        interceptors.add(block())
+    }
+}
+
+fun httpClient(block: HttpClientConfig.() -> Unit): HttpClient {
+    val config = HttpClientConfig().apply(block)
+    return HttpClient(config)
+}
+
+// Usage
+val client = httpClient {
+    baseUrl = "https://api.example.com"
+    timeout = 15_000
+    interceptor { AuthInterceptor(tokenProvider) }
+}
+```
+
+## References
+
+See skill: `kotlin-coroutines-flows` for detailed coroutine patterns.
+See skill: `android-clean-architecture` for module and layer patterns.