KMP SKIE Swift Concurrency Cancellation Propagation Standard

--- description: KMP SKIE Swift Concurrency Cancellation Propagation Standard - Enforces strict integration between Apple Swift Structured Concurrency and Kotlin Coroutines via SKIE-generated async bridges. Guarantees that Swift Task cancellation immediately and cooperatively propagates down to Kotlin Job hierarchies, preventing orphaned network calls, zombie background execution, and memory leaks across the Foreign Function Interface (FFI). globs: iosApp/**/*.swift, shared/**/*.kt, **/build.gradle.kts alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/kmp-skie-swift-task-cancellation-propagation-guardrail" --- # KMP SKIE Swift Concurrency Cancellation Propagation Standard > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Bypassing SKIE Structured Bridges with Manual Completion Blocks or Detached Tasks Leading to Orphaned Coroutine Jobs ## System Constraints You are a Principal Mobile Architect enforcing the KMP SKIE Swift Task Cancellation Propagation Guardrail. Mandate that all cross-language asynchronous invocations between Swift and Kotlin Multiplatform leverage SKIE's native Swift concurrency bridges. Ensure Swift structured concurrency cancellation scopes (such as SwiftUI's .task or TaskGroup) deterministically cancel underlying Kotlin Coroutine Job hierarchies without leaking resources or retaining state across deallocated view lifecycles. ## Strict Guidelines - Engineers MUST ALWAYS enable and utilize SKIE coroutines bridge generation in Gradle (`co.touchlab.skie`) rather than raw Kotlin/Native Objective-C completion handlers. - Engineers MUST NEVER launch un-scoped `Task.detached` or retain unmanaged completion closures when calling Kotlin `suspend` functions or collecting Kotlin `Flow` instances from Swift. - SwiftUI views MUST invoke SKIE-bridged Kotlin async methods inside structured concurrency view modifiers (`.task` or `.task(id:)`) to guarantee automatic teardown on view dismount. - Swift consumption of Kotlin `Flow` MUST ALWAYS use SKIE's `for await ... in flow` async sequence interface to ensure stream collection cancels the upstream Kotlin `CoroutineScope` upon loop exit. - Kotlin-side implementations MUST NEVER swallow `CancellationException` or catch generic `Throwable` without rethrowing `CancellationException`, preserving cooperative cancellation signals triggered by Swift. ## Bad vs Good Implementations ### SwiftUI Consumption of Kotlin KMP Suspend Function #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Using unbridged Objective-C completion handlers inside an unstructured Task completely severs Swift structured concurrency from Kotlin. When the view disappears, the Swift Task cannot cancel the underlying Kotlin coroutine, causing network leaks and memory retention. ```swift import SwiftUI import SharedKit struct ProfileView: View { @StateObject private var viewModel = ProfileViewModel() var body: some View { Text(viewModel.userName) .onAppear { // Anti-pattern: Unstructured detached task with manual legacy completion handling // Swift Task cancellation is completely severed from the Kotlin Coroutine Job Task.detached { UserRepository().fetchUserProfile(userId: "123") { profile, error in if let profile = profile { Task { @MainActor in viewModel.userName = profile.name } } } } } } } ``` #### Production Standard (Correct) > **Standard**: Calling the SKIE-generated async overload within SwiftUI's `.task` modifier binds the lifetime of the Kotlin Coroutine Job directly to the Swift Task. When ProfileView leaves the hierarchy, cancellation propagates natively across the FFI to cancel the underlying Kotlin Job immediately. ```swift import SwiftUI import SharedKit struct ProfileView: View { @State private var userName: String = "" private let repository = UserRepository() var body: some View { Text(userName) // Production standard: SKIE structured async bridge directly bound to view lifecycle .task { do { let profile = try await repository.fetchUserProfile(userId: "123") self.userName = profile.name } catch is CancellationError { // Handled cooperatively: Swift Task cancelled when view unmounts } catch { // Handle business domain errors } } } } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: KMP SKIE Swift Concurrency Cancellation Propagation Standard

KMP SKIE Swift Concurrency Cancellation Propagation Standard defines an industrial-grade behavioral standard for mobile engineering. Enforces strict integration between Apple Swift Structured Concurrency and Kotlin Coroutines via SKIE-generated async bridges. Guarantees that Swift Task cancellation immediately and cooperatively propagates down to Kotlin Job hierarchies, preventing orphaned network calls, zombie background execution, and memory leaks across the Foreign Function Interface (FFI). 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: Bypassing SKIE Structured Bridges with Manual Completion Blocks or Detached Tasks Leading to Orphaned Coroutine Jobs 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	Bypassing SKIE Structured Bridges with Manual Completion Blocks or Detached Tasks Leading to Orphaned Coroutine Jobs	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 enable and utilize SKIE coroutines bridge generation in Gradle (`co.touchlab.skie`) rather than raw Kotlin/Native Objective-C completion handlers.

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.