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frontendcritical PriorityID: svelte5-runes-cycle-fence-boundary

Svelte 5 Runes Invalidation Fence & Microtask Boundary Convergence

Enforces strict unidirectional data flow and deterministic microtask boundary fencing within Svelte 5 fine-grained reactive graphs ($state, $derived, $effect). Prohibits bidirectional state mutations inside reactive effects to eliminate cascading dependency tearing and infinite graph invalidation loops under high-frequency stream ingress.

Prohibited Anti-Pattern: Mutating Dependent $state Inside $effect Causing Microtask Invalidation Cycles and Signal Graph Tearing

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---
description: Svelte 5 Runes Invalidation Fence & Microtask Boundary Convergence - Enforces strict unidirectional data flow and deterministic microtask boundary fencing within Svelte 5 fine-grained reactive graphs ($state, $derived, $effect). Prohibits bidirectional state mutations inside reactive effects to eliminate cascading dependency tearing and infinite graph invalidation loops under high-frequency stream ingress.
globs: src/**/*.{svelte,svelte.ts,svelte.js,ts}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/svelte5-runes-cycle-fence-boundary"
---

# Svelte 5 Runes Invalidation Fence & Microtask Boundary Convergence

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Mutating Dependent $state Inside $effect Causing Microtask Invalidation Cycles and Signal Graph Tearing

## System Constraints
You are a Principal Frontend Architect enforcing strict signal graph invariants in Svelte 5. You must reject any code mutating reactive $state inside $effect blocks without explicit cycle fencing or untrack barriers. Mandate that computed values use $derived/$derived.by and high-frequency stream mutations run through bounded microtask queues.

## Strict Guidelines
- Engineers MUST ALWAYS compute reactive projections using $derived or $derived.by instead of synchronizing secondary state inside an $effect.
- Engineers MUST NOT mutate a $state variable inside an $effect that synchronously or transitively tracks that same state variable, preventing infinite update depth errors.
- Code MUST isolate downstream telemetry, logging, or foreign system sync by wrapping read dependencies in untrack() when side-effects must execute conditionally.
- Services handling high-frequency telemetry/WebSocket streams MUST buffer inputs and flush them across explicit requestAnimationFrame or queueMicrotask boundaries to prevent Svelte microtask saturation.
- Components NEVER bridge cross-store reactivity by chaining $effect triggers; orchestrate shared transactional state changes through dedicated domain actions.

## Bad vs Good Implementations
### Eliminate State Synchronization Anti-Pattern via $derived.by

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Mutating 'double' inside $effect re-triggers reactive graph passes, inducing graph tearing and microtask starvation. 'double' is a derived projection masquerading as mutable root state.
```typescript
import { untrack } from 'svelte';

// Bad: Bidirectional cycle and cascading microtask updates
let count = $state(0);
let double = $state(0);
let telemetryDispatched = $state(false);

$effect(() => {
  // Mutating tracked dependency inside effect
  double = count * 2;
  if (double > 100 && !telemetryDispatched) {
    telemetryDispatched = true;
    fetch('/api/telemetry', { method: 'POST', body: JSON.stringify({ double }) });
  }
});
```

#### Production Standard (Correct)
> **Standard**: Derives 'double' pure and synchronously using the $derived rune. The $effect exclusively houses foreign side-effects and fences off outbound telemetry using untrack() to prevent cycles.
```typescript
import { untrack } from 'svelte';

// Good: Pure derivation fence with untracked boundary dispatch
let count = $state(0);
const double = $derived(count * 2);

$effect(() => {
  const currentDouble = double;
  if (currentDouble > 100) {
    untrack(() => {
      // Side-effect safely fenced from reactive dependency graph
      navigator.sendBeacon('/api/telemetry', JSON.stringify({ double: currentDouble }));
    });
  }
});
```
Recommended MCP Servers (mcp-serverlist.com)

Equip agent with system tools to verify code for this stack.

Svelte Language Tools MCP
Provides AST inspection, compile-time validation, and diagnostic error capture for Svelte 5 runes and template reactivity.
Recommended Agent Skills (askills.dev)

Ready-to-use executable skill functions tailored to this stack.

Svelte Check CLI Tool
Runs static type checking and reactivity cycle analysis across all Svelte components.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Svelte 5 Runes Invalidation Fence & Microtask Boundary Convergence

Svelte 5 Runes Invalidation Fence & Microtask Boundary Convergence defines an industrial-grade behavioral standard for frontend engineering. Enforces strict unidirectional data flow and deterministic microtask boundary fencing within Svelte 5 fine-grained reactive graphs ($state, $derived, $effect). Prohibits bidirectional state mutations inside reactive effects to eliminate cascading dependency tearing and infinite graph invalidation loops under high-frequency stream ingress. 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: Mutating Dependent $state Inside $effect Causing Microtask Invalidation Cycles and Signal Graph Tearing 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 ModeAI Symptom (The Anti-Pattern)SeverityProduction Impact & Remedy
AI Hallucination & Deprecation DriftMutating Dependent $state Inside $effect Causing Microtask Invalidation Cycles and Signal Graph TearingCritical
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 InconsistencyAI 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:

1

Engineers MUST ALWAYS compute reactive projections using $derived or $derived.by instead of synchronizing secondary state inside an $effect.

Engineers MUST ALWAYS compute reactive projections using $derived or $derived.by instead of synchronizing secondary state inside an $effect.

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.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
2

Engineers MUST NOT mutate a $state variable inside an $effect that synchronously or transitively tracks that same state variable, preventing infinite update depth errors.

Engineers MUST NOT mutate a $state variable inside an $effect that synchronously or transitively tracks that same state variable, preventing infinite update depth errors.

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.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
3

Code MUST isolate downstream telemetry, logging, or foreign system sync by wrapping read dependencies in untrack() when side-effects must execute conditionally.

Code MUST isolate downstream telemetry, logging, or foreign system sync by wrapping read dependencies in untrack() when side-effects must execute conditionally.

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.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
4

Services handling high-frequency telemetry/WebSocket streams MUST buffer inputs and flush them across explicit requestAnimationFrame or queueMicrotask boundaries to prevent Svelte microtask saturation.

Services handling high-frequency telemetry/WebSocket streams MUST buffer inputs and flush them across explicit requestAnimationFrame or queueMicrotask boundaries to prevent Svelte microtask saturation.

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.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
5

Components NEVER bridge cross-store reactivity by chaining $effect triggers

Components NEVER bridge cross-store reactivity by chaining $effect triggers; orchestrate shared transactional state changes through dedicated domain actions.

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.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is Svelte 5 Runes Invalidation Fence & Microtask Boundary Convergence critical for AI coding assistants?

Enforces strict unidirectional data flow and deterministic microtask boundary fencing within Svelte 5 fine-grained reactive graphs ($state, $derived, $effect). Prohibits bidirectional state mutations inside reactive effects to eliminate cascading dependency tearing and infinite graph invalidation loops under high-frequency stream ingress. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (Mutating Dependent $state Inside $effect Causing Microtask Invalidation Cycles and Signal Graph Tearing) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.

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