KMP Native Coroutine ARC Scope Bridging and Bidirectional Cancellation Guardrail

--- description: KMP Native Coroutine ARC Scope Bridging and Bidirectional Cancellation Guardrail - Enforces deterministic memory deallocation and bidirectional cancellation when bridging Kotlin Multiplatform (KMP) Flows and CoroutineScopes into Swift Concurrency. Eliminates dangling native coroutine handles, cross-runtime ARC retain cycles, and silent thread pool exhaustion on iOS. globs: iosApp/**/*.swift, shared/src/iosMain/**/*.kt, **/*Bridge*.{swift,kt}, **/*Adapter*.{swift,kt}, **/*ViewModel*.swift alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/kmp-native-coroutine-arc-bridge-invariant" --- # KMP Native Coroutine ARC Scope Bridging and Bidirectional Cancellation Guardrail > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Leaking KMP CoroutineJobs in Unstructured Swift Tasks with Implicit Strong ARC Self-Captures ## System Constraints You are a Principal Software Architect enforcing the KMP Native Coroutine ARC Scope Bridging Invariant. Engineers and AI agents frequently create catastrophic memory leaks and zombie collectors when bridging Kotlin Coroutines/Flows across the Objective-C/Swift bridge into Swift Concurrency. You must strictly mandate bidirectional cancellation propagation, weak reference captures, and explicit Scope disposal via withTaskCancellationHandler or proper AsyncSequence adapter boundaries. ## Strict Guidelines - Engineers MUST ALWAYS wrap Swift-consumed Kotlin Flows in an AsyncSequence that binds Swift Task cancellation directly to the underlying Kotlin DisposableHandle/Job.cancel(). - Engineers MUST NOT invoke Kotlin suspend functions or Flow collectors inside an unstructured Task.detached without explicitly propagating structured cancellation and life-cycle ownership. - Bridging closures passing Swift closures to Kotlin callbacks MUST capture Swift dependencies weakly ([weak self]) to break cross-runtime strong reference cycles between ARC and Kotlin's Garbage Collector. - Swift ViewModels or presenters bridging Kotlin CoroutineScopes MUST explicitly invoke CoroutineScope.cancel() in their Swift deinit or when the associated SwiftUI view disappears. - Code MUST NEVER use raw, unchecked completion handlers across the C-interop boundary without defensive error handling for CancellationException to avoid unhandled NSExceptions. ## Bad vs Good Implementations ### Bridging Kotlin Flow to Swift AsyncSequence with Bidirectional Cancellation #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The Swift Task captures 'self' strongly, forming a cross-runtime retain cycle between the Kotlin FlowCollector and the Swift ViewModel. Furthermore, when the Swift UI lifecycle ends, the Kotlin Flow collection is not cancelled, silently burning network and CPU resources in the background. ```swift import SharedLibrary final class UserProfileViewModel: ObservableObject { @Published var profile: UserProfile? = nil private let repository: UserRepository init(repository: UserRepository) { self.repository = repository // BUG: Unstructured Task creates strong retain cycle and ignores scope cancellation. // If the ViewModel is deallocated, the Kotlin Flow remains active on the background thread. Task { self.repository.observeProfile().collect(collector: FlowCollector { self.profile = $0 }) { error in if let error = error { print("Flow error: \(error)") } } } } } ``` #### Production Standard (Correct) > **Standard**: Uses an AsyncStream bounded to a weak self capture. The AsyncStream's onTermination hook guarantees that cancelling the Swift Task calls handle.dispose() on the Kotlin DisposableHandle, cleanly severing the flow collector and breaking ARC retain cycles on ViewModel deinit. ```swift import SharedLibrary final class UserProfileViewModel: ObservableObject { @Published private(set) var profile: UserProfile? = nil private let repository: UserRepository private var observeTask: Task<Void, Never>? = nil init(repository: UserRepository) { self.repository = repository bindProfileStream() } private func bindProfileStream() { observeTask = Task { [weak self] in // Invariant: Bridge Kotlin Flow into an AsyncStream with explicit cancellation hook let stream = AsyncStream<UserProfile> { continuation in guard let self = self else { continuation.finish(); return } let handle = self.repository.observeProfile().subscribe( onEach: { profile in continuation.yield(profile) }, onCompletion: { error in continuation.finish() } ) continuation.onTermination = { @Sendable _ in // Enforce Swift-to-Kotlin cancellation propagation handle.dispose() } } for await profile in stream { guard !Task.isCancelled else { break } await MainActor.run { [weak self] in self?.profile = profile } } } } deinit { observeTask?.cancel() } } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: KMP Native Coroutine ARC Scope Bridging and Bidirectional Cancellation Guardrail

KMP Native Coroutine ARC Scope Bridging and Bidirectional Cancellation Guardrail defines an industrial-grade behavioral standard for mobile engineering. Enforces deterministic memory deallocation and bidirectional cancellation when bridging Kotlin Multiplatform (KMP) Flows and CoroutineScopes into Swift Concurrency. Eliminates dangling native coroutine handles, cross-runtime ARC retain cycles, and silent thread pool exhaustion on iOS. 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: Leaking KMP CoroutineJobs in Unstructured Swift Tasks with Implicit Strong ARC Self-Captures 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	Leaking KMP CoroutineJobs in Unstructured Swift Tasks with Implicit Strong ARC Self-Captures	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 Swift-consumed Kotlin Flows in an AsyncSequence that binds Swift Task cancellation directly to the underlying Kotlin DisposableHandle/Job.cancel().

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.