Swift 6 Complete Concurrency Actor-Isolated Bridge Guardrail

--- description: Swift 6 Complete Concurrency Actor-Isolated Bridge Guardrail - Enforces compiler-level Sendable validation and strict actor isolation across native bridge boundaries (React Native TurboModules, Flutter Platform Channels, and WebKit script handlers) in Swift 6. Eliminates multithreaded data races by forbidding @unchecked Sendable escapes, unisolated mutable bridge state, and non-isolated async callbacks. Guarantees that all payloads crossing the boundary are strictly Sendable value types and mutation occurs exclusively within designated actors. globs: ios/**/*.swift, macos/**/*.swift, **/*Bridge*.swift, **/*Module*.swift, **/*Channel*.swift alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/swift-6-complete-concurrency-actor-bridge" --- # Swift 6 Complete Concurrency Actor-Isolated Bridge Guardrail > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Escaping Mutable Platform Channel or TurboModule State Across Unisolated Concurrent Contexts ## System Constraints You are a Principal Mobile Architect enforcing Swift 6 Complete Concurrency across native bridge boundaries. You must strictly mandate that all bridge boundaries (React Native Nitro/TurboModules, Flutter MethodChannels, WKScriptMessageHandler) isolate mutable state within dedicated global or custom actors. You must prohibit unchecked Sendable conformance, mutable reference types in boundary payloads, and synchronous bridging methods that mutate cross-thread shared state. Ensure all build flags require SWIFT_STRICT_CONCURRENCY=complete. ## Strict Guidelines - Engineers MUST ALWAYS isolate bridge entrypoints and state stores to a dedicated custom actor or @MainActor when interacting with UI runloops. - Engineers MUST NOT mark classes crossing bridge boundaries with @unchecked Sendable to suppress compiler diagnostics without formal OSAllocatedUnfairLock memory barriers. - Code MUST ensure all bridge transfer DTOs, arguments, and return types conform to Sendable using immutable structs, primitives, or Sendable enums. - Services MUST route asynchronous callback handlers (e.g., FlutterResult, RCTPromiseResolveBlock) across boundary hops via isolated actor methods with explicit nonisolated async adaptors. - Components NEVER capture un-isolated reference types inside Task closures dispatched from bridge entrypoints. ## Bad vs Good Implementations ### React Native / Flutter Bridge State Isolation and Sendable Validation #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The class is non-isolated and handles bridge execution on arbitrary threads. It mutates reference state (cache) without synchronization, accepts non-Sendable `[String: Any]` payloads that contain arbitrary reference types, and captures self in an untracked concurrent closure, causing data races under Swift 6. ```swift import Foundation // ANTI-PATTERN: Unisolated class, mutable shared state across threads, // non-Sendable payload escape, and non-isolated bridge handler. class NativeBridgeModule { private var cache: [String: Any] = [:] // Race condition hazard func handlePlatformCall(payload: [String: Any], completion: @escaping ([String: Any]) -> Void) { DispatchQueue.global().async { let id = payload["id"] as? String ?? "" self.cache[id] = payload["data"] // Thread-safety violation let result = ["status": "success", "cachedId": id] DispatchQueue.main.async { completion(result) } } } } ``` #### Production Standard (Correct) > **Standard**: Transforms the payload to an immutable Sendable struct, encapsulates mutable state inside an isolated actor (`BridgeStore`), and exposes an async API bound to `@MainActor` ensuring compile-time data race elimination under Swift 6 Complete Concurrency. ```swift import Foundation // PRODUCTION FIX: Explicit Sendable payload contract and actor-isolated state store public struct BridgePayload: Sendable, Codable { public let id: String public let data: String public init(id: String, data: String) { self.id = id self.data = data } } public struct BridgeResponse: Sendable, Codable { public let status: String public let cachedId: String } public actor BridgeStore { private var cache: [String: String] = [:] public func save(id: String, value: String) { cache[id] = value } public func retrieve(id: String) -> String? { cache[id] } } @MainActor public final class NativeBridgeModule { private let store: BridgeStore public init(store: BridgeStore = BridgeStore()) { self.store = store } public func handlePlatformCall(payload: BridgePayload) async -> BridgeResponse { await store.save(id: payload.id, value: payload.data) return BridgeResponse(status: "success", cachedId: payload.id) } } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Swift 6 Complete Concurrency Actor-Isolated Bridge Guardrail

Swift 6 Complete Concurrency Actor-Isolated Bridge Guardrail defines an industrial-grade behavioral standard for mobile engineering. Enforces compiler-level Sendable validation and strict actor isolation across native bridge boundaries (React Native TurboModules, Flutter Platform Channels, and WebKit script handlers) in Swift 6. Eliminates multithreaded data races by forbidding @unchecked Sendable escapes, unisolated mutable bridge state, and non-isolated async callbacks. Guarantees that all payloads crossing the boundary are strictly Sendable value types and mutation occurs exclusively within designated actors. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Escaping Mutable Platform Channel or TurboModule State Across Unisolated Concurrent Contexts Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Escaping Mutable Platform Channel or TurboModule State Across Unisolated Concurrent Contexts	Critical	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

Engineers MUST ALWAYS isolate bridge entrypoints and state stores to a dedicated custom actor or @MainActor when interacting with UI runloops.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.