Kotlin Multiplatform 2.1 Swift AsyncStream Cancellation Bridge Standard

--- description: Kotlin Multiplatform 2.1 Swift AsyncStream Cancellation Bridge Standard - Enforces strict cooperative cancellation bridging between Kotlin Coroutines and Swift Concurrency via SKIE or explicit Job termination hooks in AsyncStream.onTermination handlers. Without this invariant, Swift Task aborts leave underlying Kotlin Job hierarchies running indefinitely, causing silent thread pool starvation and memory leaks across the Objective-C/Swift ABI bridge. globs: iosApp/**/*.swift, shared/src/iosMain/**/*.kt, shared/src/commonMain/**/*.kt, **/*Bridge*.swift, **/*Repository*.swift alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/kmp-swift-asyncstream-cancellation-bridge" --- # Kotlin Multiplatform 2.1 Swift AsyncStream Cancellation Bridge Standard > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Orphaned Kotlin Coroutine Jobs Surviving Cancelled Swift AsyncStream Tasks ## System Constraints You are a Principal Mobile Architect enforcing the KMP 2.1 Swift AsyncStream Cancellation Bridge Standard. Mandate that every Swift AsyncStream bridging a Kotlin Coroutine Flow or Job explicitly registers an `onTermination` handler or leverages verified SKIE zero-cost bridge cancellation. Reject any unmanaged bridging where Swift Task abortion fails to cancel the underlying Kotlin `Job` / `DisposableHandle`. ## Strict Guidelines - Engineers MUST ALWAYS register an `onTermination` closure when wrapping a Kotlin Flow or Suspend adapter inside a Swift `AsyncStream` or `AsyncThrowingStream`. - Engineers MUST NOT discard or ignore the returned Kotlin `Cancellable` or `DisposableHandle` when starting collection on an iOS-exported Kotlin coroutine. - Swift bridging code MUST invoke `job.cancel(cause: nil)` inside `continuation.onTermination = { _ in ... }` immediately upon stream completion or task cancellation. - Kotlin-facing bridge protocols MUST return an explicit handle (e.g., `DisposableHandle` or `Job`) or consume a shared `CancellationHook` to allow the Swift foreign function interface (FFI) to trigger cooperative cancellation. - Components NEVER assume Swift's `Task.isCancelled` automatically propagates across the Kotlin Native runtime boundary unless SKIE coroutine cancellation interop is explicitly configured and verified in `build.gradle.kts`. ## Bad vs Good Implementations ### Bridging Kotlin Flow to Swift AsyncStream with Lifecycle Management #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: When the Swift Task wrapping observeUserSession() is cancelled (e.g., SwiftUI View unmounts via .task modifier), the continuation terminates but the underlying Kotlin Flow collector continues running indefinitely on a Kotlin dispatch thread, causing resource exhaustion. ```swift // BAD: Kotlin Coroutine Job is discarded; Task cancellation leaves Kotlin Flow active in background func observeUserSession() -> AsyncStream<UserSession> { AsyncStream { continuation in let watcher = sessionRepository.observeSession() watcher.watch { session in continuation.yield(session) } // Anti-pattern: No onTermination registered, watcher and Kotlin Job leak on Swift cancellation } } ``` #### Production Standard (Correct) > **Standard**: The returned DisposableHandle (representing the underlying Kotlin Job) is retained and explicitly cancelled within continuation.onTermination. When the Swift Task aborts, the signal immediately reaches the Kotlin Native runtime. ```swift // GOOD: Cooperative cancellation bridged through DisposableHandle in onTermination func observeUserSession() -> AsyncStream<UserSession> { AsyncStream { continuation in let cancellable = sessionRepository.observeSession().collectKotlinStream( onEach: { session in continuation.yield(session) }, onCompletion: { error in continuation.finish() } ) continuation.onTermination = { @Sendable _ in // Invariant: Swift cancellation terminates the Kotlin Job hierarchy immediately cancellable.dispose() } } } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Kotlin Multiplatform 2.1 Swift AsyncStream Cancellation Bridge Standard

Kotlin Multiplatform 2.1 Swift AsyncStream Cancellation Bridge Standard defines an industrial-grade behavioral standard for mobile engineering. Enforces strict cooperative cancellation bridging between Kotlin Coroutines and Swift Concurrency via SKIE or explicit Job termination hooks in AsyncStream.onTermination handlers. Without this invariant, Swift Task aborts leave underlying Kotlin Job hierarchies running indefinitely, causing silent thread pool starvation and memory leaks across the Objective-C/Swift ABI bridge. 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: Orphaned Kotlin Coroutine Jobs Surviving Cancelled Swift AsyncStream Tasks 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	Orphaned Kotlin Coroutine Jobs Surviving Cancelled Swift AsyncStream Tasks	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 register an `onTermination` closure when wrapping a Kotlin Flow or Suspend adapter inside a Swift `AsyncStream` or `AsyncThrowingStream`.

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.