Capacitor 7 Main-Thread JNI Decoupling & Background Task Standard

--- description: Capacitor 7 Main-Thread JNI Decoupling & Background Task Standard - Enforces non-blocking native bridge execution boundaries and managed OS background task lifecycles in Capacitor 7. Eliminates UI thread deadlocks, Android Application Not Responding (ANR) violations, and iOS Watchdog (0x8badf00d) terminations caused by synchronous JNI/bridge executions during heavy workloads and background transitions. globs: src/**/*.{ts,tsx}, android/app/src/main/java/**/*.java, android/app/src/main/kotlin/**/*.kt, ios/App/App/**/*.swift alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/capacitor-7-jni-decoupling-background-task-standard" --- # Capacitor 7 Main-Thread JNI Decoupling & Background Task Standard > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Executing heavy bridge operations synchronously on native UI threads without background task assertions ## System Constraints You are a Principal Mobile Architect enforcing Capacitor 7 native bridge invariants. Mandate strict UI thread decoupling across the Web-to-Native bridge: all custom native plugin methods executing I/O, heavy computation, or JNI operations must dispatch to background worker threads, and client-side bridge invocations occurring across lifecycle transitions must acquire explicit OS background execution leases with strict timeouts. ## Strict Guidelines - Engineers MUST ALWAYS wrap native bridge invocations initiated during background transitions inside explicit background task assertions (e.g., native beginBackgroundTask or @capacitor/app background state handlers) with fail-safe timeouts. - Engineers MUST NOT execute heavy native JNI bridge invocations or synchronous disk/network I/O on the native UI/Main thread (Android MainLooper / iOS MainQueue). - Native plugin implementations MUST dispatch heavy work via `bridge.executeOnBackgroundThread` (Android) or `DispatchQueue.global()` (iOS) before posting results back to PluginCall. - Frontend bridge consumers MUST implement deterministic timeout boundaries and AbortController signals for every long-running plugin call to prevent hanging promise chains in WebKit. - Components NEVER trigger synchronous native bridge calls directly within React/Vue render cycles or high-frequency frame events (e.g., scroll, requestAnimationFrame). ## Bad vs Good Implementations ### Decoupled Background Bridge Synchronization with Fail-Safe Timeout #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Awaiting unmanaged, sequential bridge calls during app backgrounding blocks the native lifecycle delegate. iOS kills the app within seconds (Watchdog termination 0x8badf00d), and Android risks bridge disconnection and ANRs. ```typescript import { App } from '@capacitor/app'; import { Filesystem } from '@capacitor/filesystem'; import { DataSyncPlugin } from './plugins/data-sync'; // ANTI-PATTERN: Direct heavy bridge execution on background transition without task lease or timeout App.addListener('appStateChange', async ({ isActive }) => { if (!isActive) { // Synchronously invoking heavy bridge calls during backgrounding causes OS termination (0x8badf00d / ANR) const cache = await Filesystem.readFile({ path: 'pending_sync.json' }); await DataSyncPlugin.uploadPendingRecords({ payload: cache.data }); } }); ``` #### Production Standard (Correct) > **Standard**: Acquires a native OS background lease, establishes a hard deadline via AbortController, and guarantees resource cleanup in the finally block before OS-enforced termination. ```typescript import { App } from '@capacitor/app'; import { Filesystem } from '@capacitor/filesystem'; import { DataSyncPlugin } from './plugins/data-sync'; const BACKGROUND_SYNC_TIMEOUT_MS = 25000; App.addListener('appStateChange', async ({ isActive }) => { if (isActive) return; const controller = new AbortController(); const timeoutId = setTimeout(() => controller.abort(), BACKGROUND_SYNC_TIMEOUT_MS); let taskId: string | null = null; try { // Acquire OS background execution lease via Capacitor native bridge boundary const lease = await DataSyncPlugin.beginBackgroundLease(); taskId = lease.taskId; const cache = await Filesystem.readFile({ path: 'pending_sync.json' }); // Execute decoupled background sync with strict timeout enforcement await Promise.race([ DataSyncPlugin.uploadPendingRecords({ payload: cache.data, taskId: lease.taskId }), new Promise((_, reject) => { controller.signal.addEventListener('abort', () => { reject(new Error('Background execution lease exceeded timeout')); }); }) ]); } catch (error) { console.error('Safe background sync failure / deadline reached:', error); } finally { clearTimeout(timeoutId); if (taskId) { // Mandatory release of OS execution assertion to prevent watchdog slaughter await DataSyncPlugin.endBackgroundLease({ taskId }); } } }); ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Capacitor 7 Main-Thread JNI Decoupling & Background Task Standard

Capacitor 7 Main-Thread JNI Decoupling & Background Task Standard defines an industrial-grade behavioral standard for mobile engineering. Enforces non-blocking native bridge execution boundaries and managed OS background task lifecycles in Capacitor 7. Eliminates UI thread deadlocks, Android Application Not Responding (ANR) violations, and iOS Watchdog (0x8badf00d) terminations caused by synchronous JNI/bridge executions during heavy workloads and background transitions. 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: Executing heavy bridge operations synchronously on native UI threads without background task assertions 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	Executing heavy bridge operations synchronously on native UI threads without background task assertions	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 native bridge invocations initiated during background transitions inside explicit background task assertions (e.g., native beginBackgroundTask or @capacitor/app background state handlers) with fail-safe timeouts.

Engineers MUST ALWAYS wrap native bridge invocations initiated during background transitions inside explicit background task assertions (e.g., native beginBackgroundTask or @capacitor/app background state handlers) with fail-safe timeouts.

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.