feat: add Swift language-specific rules

Add 5 rule files for Swift following the established pattern used by
TypeScript, Python, and Go rule sets. Covers Swift 6 strict concurrency,
Swift Testing framework, protocol-oriented patterns, Keychain-based
secret management, and SwiftFormat/SwiftLint hooks.

rules/README.md

@@ -17,7 +17,8 @@ rules/
 │   └── security.md
 ├── typescript/      # TypeScript/JavaScript specific
 ├── python/          # Python specific
-└── golang/          # Go specific
+├── golang/          # Go specific
+└── swift/           # Swift specific
 ```
 
 - **common/** contains universal principles — no language-specific code examples.
@@ -32,6 +33,7 @@ rules/
 ./install.sh typescript
 ./install.sh python
 ./install.sh golang
+./install.sh swift
 
 # Install multiple languages at once
 ./install.sh typescript python
@@ -53,6 +55,7 @@ cp -r rules/common ~/.claude/rules/common
 cp -r rules/typescript ~/.claude/rules/typescript
 cp -r rules/python ~/.claude/rules/python
 cp -r rules/golang ~/.claude/rules/golang
+cp -r rules/swift ~/.claude/rules/swift
 
 # Attention ! ! ! Configure according to your actual project requirements; the configuration here is for reference only.
 ```

rules/swift/coding-style.md

@@ -0,0 +1,47 @@
+---
+paths:
+  - "**/*.swift"
+  - "**/Package.swift"
+---
+# Swift Coding Style
+
+> This file extends [common/coding-style.md](../common/coding-style.md) with Swift specific content.
+
+## Formatting
+
+- **SwiftFormat** for auto-formatting, **SwiftLint** for style enforcement
+- `swift-format` is bundled with Xcode 16+ as an alternative
+
+## Immutability
+
+- Prefer `let` over `var` — define everything as `let` and only change to `var` if the compiler requires it
+- Use `struct` with value semantics by default; use `class` only when identity or reference semantics are needed
+
+## Naming
+
+Follow [Apple API Design Guidelines](https://www.swift.org/documentation/api-design-guidelines/):
+
+- Clarity at the point of use — omit needless words
+- Name methods and properties for their roles, not their types
+- Use `static let` for constants over global constants
+
+## Error Handling
+
+Use typed throws (Swift 6+) and pattern matching:
+
+```swift
+func load(id: String) throws(LoadError) -> Item {
+    guard let data = try? read(from: path) else {
+        throw .fileNotFound(id)
+    }
+    return try decode(data)
+}
+```
+
+## Concurrency
+
+Enable Swift 6 strict concurrency checking. Prefer:
+
+- `Sendable` value types for data crossing isolation boundaries
+- Actors for shared mutable state
+- Structured concurrency (`async let`, `TaskGroup`) over unstructured `Task {}`

rules/swift/hooks.md

@@ -0,0 +1,20 @@
+---
+paths:
+  - "**/*.swift"
+  - "**/Package.swift"
+---
+# Swift Hooks
+
+> This file extends [common/hooks.md](../common/hooks.md) with Swift specific content.
+
+## PostToolUse Hooks
+
+Configure in `~/.claude/settings.json`:
+
+- **SwiftFormat**: Auto-format `.swift` files after edit
+- **SwiftLint**: Run lint checks after editing `.swift` files
+- **swift build**: Type-check modified packages after edit
+
+## Warning
+
+Flag `print()` statements — use `os.Logger` or structured logging instead for production code.

rules/swift/patterns.md

@@ -0,0 +1,66 @@
+---
+paths:
+  - "**/*.swift"
+  - "**/Package.swift"
+---
+# Swift Patterns
+
+> This file extends [common/patterns.md](../common/patterns.md) with Swift specific content.
+
+## Protocol-Oriented Design
+
+Define small, focused protocols. Use protocol extensions for shared defaults:
+
+```swift
+protocol Repository: Sendable {
+    associatedtype Item: Identifiable & Sendable
+    func find(by id: Item.ID) async throws -> Item?
+    func save(_ item: Item) async throws
+}
+```
+
+## Value Types
+
+- Use structs for data transfer objects and models
+- Use enums with associated values to model distinct states:
+
+```swift
+enum LoadState<T: Sendable>: Sendable {
+    case idle
+    case loading
+    case loaded(T)
+    case failed(Error)
+}
+```
+
+## Actor Pattern
+
+Use actors for shared mutable state instead of locks or dispatch queues:
+
+```swift
+actor Cache<Key: Hashable & Sendable, Value: Sendable> {
+    private var storage: [Key: Value] = [:]
+
+    func get(_ key: Key) -> Value? { storage[key] }
+    func set(_ key: Key, value: Value) { storage[key] = value }
+}
+```
+
+## Dependency Injection
+
+Inject protocols with default parameters — production uses defaults, tests inject mocks:
+
+```swift
+struct UserService {
+    private let repository: any UserRepository
+
+    init(repository: any UserRepository = DefaultUserRepository()) {
+        self.repository = repository
+    }
+}
+```
+
+## References
+
+See skill: `swift-actor-persistence` for actor-based persistence patterns.
+See skill: `swift-protocol-di-testing` for protocol-based DI and testing.

rules/swift/security.md

@@ -0,0 +1,33 @@
+---
+paths:
+  - "**/*.swift"
+  - "**/Package.swift"
+---
+# Swift Security
+
+> This file extends [common/security.md](../common/security.md) with Swift specific content.
+
+## Secret Management
+
+- Use **Keychain Services** for sensitive data (tokens, passwords, keys) — never `UserDefaults`
+- Use environment variables or `.xcconfig` files for build-time secrets
+- Never hardcode secrets in source — decompilation tools extract them trivially
+
+```swift
+let apiKey = ProcessInfo.processInfo.environment["API_KEY"]
+guard let apiKey, !apiKey.isEmpty else {
+    fatalError("API_KEY not configured")
+}
+```
+
+## Transport Security
+
+- App Transport Security (ATS) is enforced by default — do not disable it
+- Use certificate pinning for critical endpoints
+- Validate all server certificates
+
+## Input Validation
+
+- Sanitize all user input before display to prevent injection
+- Use `URL(string:)` with validation rather than force-unwrapping
+- Validate data from external sources (APIs, deep links, pasteboard) before processing

rules/swift/testing.md

@@ -0,0 +1,45 @@
+---
+paths:
+  - "**/*.swift"
+  - "**/Package.swift"
+---
+# Swift Testing
+
+> This file extends [common/testing.md](../common/testing.md) with Swift specific content.
+
+## Framework
+
+Use **Swift Testing** (`import Testing`) for new tests. Use `@Test` and `#expect`:
+
+```swift
+@Test("User creation validates email")
+func userCreationValidatesEmail() throws {
+    #expect(throws: ValidationError.invalidEmail) {
+        try User(email: "not-an-email")
+    }
+}
+```
+
+## Test Isolation
+
+Each test gets a fresh instance — set up in `init`, tear down in `deinit`. No shared mutable state between tests.
+
+## Parameterized Tests
+
+```swift
+@Test("Validates formats", arguments: ["json", "xml", "csv"])
+func validatesFormat(format: String) throws {
+    let parser = try Parser(format: format)
+    #expect(parser.isValid)
+}
+```
+
+## Coverage
+
+```bash
+swift test --enable-code-coverage
+```
+
+## Reference
+
+See skill: `swift-protocol-di-testing` for protocol-based dependency injection and mock patterns with Swift Testing.