Add lightweight clients reference and index entry

Introduces a new reference file describing the lightweight, closure-based client pattern for SwiftUI apps. Updates the components index to include a link to this new guidance, supporting easier discovery and usage of small, testable API clients.

swiftui-ui-patterns/references/components-index.md

@@ -26,6 +26,7 @@ Use this file to find component-specific guidance. Each entry lists when to use
 - Deep links and URL routing: `references/deeplinks.md` — Use for in-app navigation from URLs.
 - Title menus: `references/title-menus.md` — Use for filter or context menus in the navigation title.
 - Loading & placeholders: `references/loading-placeholders.md` — Use for redacted skeletons, empty states, and loading UX.
+- Lightweight clients: `references/lightweight-clients.md` — Use for small, closure-based API clients injected into stores.
 
 ## Planned components (create files as needed)
 

swiftui-ui-patterns/references/lightweight-clients.md

@@ -0,0 +1,93 @@
+# Lightweight Clients (Closure-Based)
+
+Use this pattern to keep networking or service dependencies simple and testable without introducing a full view model or heavy DI framework. It works well for SwiftUI apps where you want a small, composable API surface that can be swapped in previews/tests.
+
+## Intent
+- Provide a tiny "client" type made of async closures.
+- Keep business logic in a store or feature layer, not the view.
+- Enable easy stubbing in previews/tests.
+
+## Minimal shape
+```swift
+struct SomeClient {
+    var fetchItems: (_ limit: Int) async throws -> [Item]
+    var search: (_ query: String, _ limit: Int) async throws -> [Item]
+}
+
+extension SomeClient {
+    static func live(baseURL: URL = URL(string: "https://example.com")!) -> SomeClient {
+        let session = URLSession.shared
+        return SomeClient(
+            fetchItems: { limit in
+                // build URL, call session, decode
+            },
+            search: { query, limit in
+                // build URL, call session, decode
+            }
+        )
+    }
+}
+```
+
+## Usage pattern
+```swift
+@MainActor
+@Observable final class ItemsStore {
+    enum LoadState { case idle, loading, loaded, failed(String) }
+
+    var items: [Item] = []
+    var state: LoadState = .idle
+    private let client: SomeClient
+
+    init(client: SomeClient) {
+        self.client = client
+    }
+
+    func load(limit: Int = 20) async {
+        state = .loading
+        do {
+            items = try await client.fetchItems(limit)
+            state = .loaded
+        } catch {
+            state = .failed(error.localizedDescription)
+        }
+    }
+}
+```
+
+```swift
+struct ContentView: View {
+    @Environment(ItemsStore.self) private var store
+
+    var body: some View {
+        List(store.items) { item in
+            Text(item.title)
+        }
+        .task { await store.load() }
+    }
+}
+```
+
+```swift
+@main
+struct MyApp: App {
+    @State private var store = ItemsStore(client: .live())
+
+    var body: some Scene {
+        WindowGroup {
+            ContentView()
+                .environment(store)
+        }
+    }
+}
+```
+
+## Guidance
+- Keep decoding and URL-building in the client; keep state changes in the store.
+- Make the store accept the client in `init` and keep it private.
+- Avoid global singletons; use `.environment` for store injection.
+- If you need multiple variants (mock/stub), add `static func mock(...)`.
+
+## Pitfalls
+- Don’t put UI state in the client; keep state in the store.
+- Don’t capture `self` or view state in the client closures.