Kotlin Multiplatform Swift-Export ARC Weak-Boundary Guardrail

--- description: Kotlin Multiplatform Swift-Export ARC Weak-Boundary Guardrail - Eliminates cross-runtime memory retention cycles between Apple Swift ARC and Kotlin/Native GC across direct Swift-Export interop boundaries. Mandates explicit weak references and structured cancellation handles on bidirectional state streams, listener interfaces, and async continuations. Enforces strict lifecycle-bound cleanup to prevent foreign-reference root leaks in Kotlin/Native's tracing garbage collector. 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-swift-export-arc-weak-boundary-guardrail" --- # Kotlin Multiplatform Swift-Export ARC Weak-Boundary Guardrail > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Cross-Runtime Memory Leak via Strong Closure Capture of Swift Self in Kotlin Native StateFlow Observers ## System Constraints You are a Principal Mobile Architect enforcing ARC and Kotlin/Native GC boundary safety across Kotlin Multiplatform Swift-Export bindings. You must prevent cross-runtime reference cycles caused by ARC strong closures capturing Swift classes while bridging into Kotlin/Native roots. ## Strict Guidelines - Engineers MUST ALWAYS capture `[weak self]` in any Swift closure or Task that bridges Kotlin Flows, StateFlows, or callbacks. - Engineers MUST NOT pass strong Swift object references directly into long-lived Kotlin/Native singletons or shared CoroutineScopes without explicit lifecycle dissociation. - Code MUST explicitly cancel Kotlin Native `Job` or Swift `Task` observation subscriptions upon Swift view deinitialization or `.onDisappear`. - Services exposing Kotlin StateFlow to Swift-Export MUST provide deterministic disposal hooks (`close()`, `cancel()`, or `clear()`) that purge foreign reference roots. - Components NEVER store direct Swift closures as permanent listener fields in Kotlin classes without a weak reference wrapper or explicit unregister mechanism. ## Bad vs Good Implementations ### Swift-Export StateFlow Observation Across ARC/GC Boundary #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The Task strongly captures `self`, while `self` strongly retains `sharedVm`. Because Swift-Export bridges `sharedVm.state` as an asynchronous stream rooted in Kotlin/Native GC, the Swift closure context remains referenced indefinitely by the active stream continuation, creating an uncollectable cross-runtime leak between Swift ARC and Kotlin GC. ```swift import SwiftUI import SharedKit @MainActor final class ProfileViewModelWrapper: ObservableObject { private let sharedVm: ProfileViewModel @Published var state: ProfileState init(sharedVm: ProfileViewModel) { self.sharedVm = sharedVm self.state = sharedVm.state.value // ANTI-PATTERN: Strong capture of self in un-scoped Task combined with Kotlin Native Flow // creates a cross-runtime cycle: Swift VM -> Kotlin VM -> Swift Task -> Swift VM Task { for await nextState in self.sharedVm.state { self.state = nextState } } } } ``` #### Production Standard (Correct) > **Standard**: Capturing `[weak self]` prevents the asynchronous loop from pinning the Swift wrapper in memory. Maintaining and cancelling the `Task` handle in `deinit` guarantees that the Kotlin/Native stream continuation terminates, dropping the foreign reference root in the Kotlin Native runtime. ```swift import SwiftUI import SharedKit @MainActor final class ProfileViewModelWrapper: ObservableObject { private let sharedVm: ProfileViewModel private var observationTask: Task<Void, Never>? @Published var state: ProfileState init(sharedVm: ProfileViewModel) { self.sharedVm = sharedVm self.state = sharedVm.state.value // PRODUCTION GUARDRAIL: Weak capture of self + explicit cancellation handle self.observationTask = Task { [weak self] in for await nextState in sharedVm.state { guard !Task.isCancelled, let self else { break } self.state = nextState } } } deinit { // Deterministically sever ARC-to-Kotlin GC bridge reference observationTask?.cancel() sharedVm.onCleared() } } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Kotlin Multiplatform Swift-Export ARC Weak-Boundary Guardrail

Kotlin Multiplatform Swift-Export ARC Weak-Boundary Guardrail defines an industrial-grade behavioral standard for mobile engineering. Eliminates cross-runtime memory retention cycles between Apple Swift ARC and Kotlin/Native GC across direct Swift-Export interop boundaries. Mandates explicit weak references and structured cancellation handles on bidirectional state streams, listener interfaces, and async continuations. Enforces strict lifecycle-bound cleanup to prevent foreign-reference root leaks in Kotlin/Native's tracing garbage collector. 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: Cross-Runtime Memory Leak via Strong Closure Capture of Swift Self in Kotlin Native StateFlow Observers 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	Cross-Runtime Memory Leak via Strong Closure Capture of Swift Self in Kotlin Native StateFlow Observers	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 capture `[weak self]` in any Swift closure or Task that bridges Kotlin Flows, StateFlows, or callbacks.

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.