KMP StateFlow to Swift 6 Actor Bridge Thread-Safety Invariant

--- description: KMP StateFlow to Swift 6 Actor Bridge Thread-Safety Invariant - Enforces strict concurrency isolation and explicit cancellation semantics when consuming Kotlin Multiplatform (KMP) StateFlow streams within Swift 6 Actor environments. Prevents data-race thread hops, silent cancellation leakage, and Swift runtime assertion crashes caused by unshielded non-Sendable Kotlin coroutine job handles passing through isolated boundaries. globs: iosApp/**/*.swift, shared/src/iosMain/**/*.kt, shared/src/commonMain/**/*.kt alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/kmp-stateflow-swift-actor-bridge-guardrail" --- # KMP StateFlow to Swift 6 Actor Bridge Thread-Safety Invariant > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Directly Collecting KMP StateFlow within Swift 6 Actors Without Sendable Wrappers or Explicit Task Lifecycle Binding ## System Constraints You are a Principal Mobile Architect enforcing absolute memory safety and thread confinement when bridging Kotlin Multiplatform (KMP) StateFlow pipelines into Swift 6 Concurrency isolated Actor runtimes. Never allow direct observation of KMP flows via unstructured Task closures or raw callbacks that bypass Swift 6 complete concurrency checks. Mandate an explicit AsyncSequence wrapper that projects deeply Sendable Swift value models and cleanly bridges Kotlin Job cancellation. ## Strict Guidelines - Engineers MUST ALWAYS wrap Kotlin StateFlow/SharedFlow references in an AsyncSequence bridge that guarantees Sendable-conformant value emissions at the Swift boundary. - Engineers MUST NOT cross Swift Actor isolation domains with raw Kotlin Native job handles (e.g., kotlinx.coroutines.Job) or reference types lacking explicit @unchecked Sendable verification. - Swift side consumers MUST wrap flow emissions into explicit isolated Actor domains or @MainActor view models using structured Task lifecycles that guarantee Kotlin job cancellation upon Task deinit. - Kotlin iOS bridge adaptors MUST use skie:flow or custom CPointer-safe callbacks backed by Dispatchers.Main.immediate or thread-confined dispatching to prevent foreign-thread mutating state crashes. - Components NEVER collect infinite Kotlin StateFlow instances inside detached Swift Tasks (Task.detached) without retaining and propagating an explicit Swift-to-Kotlin cancellation token. ## Bad vs Good Implementations ### Bridging KMP StateFlow into a Swift 6 MainActor View Model #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Kotlin's raw .watch or callback bridge executes on a foreign Darwin background thread. Directly assigning to an isolated @MainActor property causes memory corruption and runtime crashes under Swift 6 strict concurrency checks, with no cancellation tethered to the view model lifecycle. ```swift // ANTI-PATTERN: Unstructured Task leaking Kotlin Disposable/Job, non-Sendable reference hopping into Swift MainActor import SharedKit @MainActor final class UserViewModel: ObservableObject { @Published private(set) var state: UserState = .initial private let repository: UserRepository init(repository: UserRepository) { self.repository = repository // Unsafe: Bypasses Swift 6 Concurrency checks and leaks memory repository.userStateFlow.watch { [weak self] state in // Invoked from foreign Kotlin/Native worker thread, causing race condition crash self?.state = state } } } ``` #### Production Standard (Correct) > **Standard**: Consumes the Kotlin StateFlow through a structured AsyncSequence. Values are mapped into Sendable Swift value types, updates remain strictly on the @MainActor isolation domain, and cancellation immediately stops the underlying Kotlin flow emission on deallocation. ```swift // PRODUCTION STANDARD: Strong AsyncSequence bridging with Sendable value transformation and structured Task cancellation import SharedKit @MainActor final class UserViewModel: ObservableObject { @Published private(set) var state: UserStateValue = .initial private let repository: UserRepository private var stateObserverTask: Task<Void, Never>? init(repository: UserRepository) { self.repository = repository startObservingState() } private func startObservingState() { // Structured cancellation tied to ViewModel lifecycle stateObserverTask = Task { [weak self, repository] in // SKIE or custom AsyncSequence emitting strictly Sendable structs for await rawState in repository.userStateFlow { guard !Task.isCancelled else { break } guard let self = self else { return } // Thread-confined safe update on @MainActor self.state = UserStateValue(from: rawState) } } } deinit { stateObserverTask?.cancel() } } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: KMP StateFlow to Swift 6 Actor Bridge Thread-Safety Invariant

KMP StateFlow to Swift 6 Actor Bridge Thread-Safety Invariant defines an industrial-grade behavioral standard for mobile engineering. Enforces strict concurrency isolation and explicit cancellation semantics when consuming Kotlin Multiplatform (KMP) StateFlow streams within Swift 6 Actor environments. Prevents data-race thread hops, silent cancellation leakage, and Swift runtime assertion crashes caused by unshielded non-Sendable Kotlin coroutine job handles passing through isolated boundaries. 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: Directly Collecting KMP StateFlow within Swift 6 Actors Without Sendable Wrappers or Explicit Task Lifecycle Binding 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	Directly Collecting KMP StateFlow within Swift 6 Actors Without Sendable Wrappers or Explicit Task Lifecycle Binding	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 wrap Kotlin StateFlow/SharedFlow references in an AsyncSequence bridge that guarantees Sendable-conformant value emissions at the Swift boundary.

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.