inp.unyielded long task

inp.unyielded-long-task

Rule ID: inp.unyielded-long-task Severity: WARN Category: inp Target Standards: W3C Cooperative Scheduling Controller (scheduler.yield), Google Chrome Core Web Vitals (Long Tasks & Input Responsiveness), Main-Thread Cooperative Concurrency Invariants

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1. Overview & Core Invariant

Long task processing large arrays without cooperative scheduling yields stalls main-thread responsiveness

Core Invariant:

"Long execution tasks triggered by or affecting user interactions must periodically yield control to the browser event loop via cooperative scheduling boundaries."

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2. Technical Grounding & Engine Realities

Long tasks running uninterrupted on the main thread (> 50ms) prevent the browser from acknowledging new user inputs (clicks, keypresses, taps) or rendering visual updates.

When user actions initiate extensive batch computations, running the entire process synchronously locks the page until completion, producing high Interaction to Next Paint (INP) latency.

By periodically pausing execution using modern cooperative scheduling: 'await (window.scheduler?.yield?.() ?? new Promise(r => setTimeout(r, 0)))', the browser is given immediate opportunities to handle pending user inputs and paint frames before continuing task work.

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3. Vulnerability & Risk Taxonomy

Risk Vector	Severity	Impact
Main-Thread Input Starvation	HIGH	Long uninterrupted execution loops starve the browser input queue, leaving pages unresponsive during batch processing.
High INP & Dropped Frames	MEDIUM	Presentation of user feedback is blocked for hundreds of milliseconds, breaching the 200ms INP threshold.

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4. Non-Compliant Code Patterns (Bad Examples)

TS (Long calculation loop over large dataset without cooperative yield):

function processLargeArray(items: string[]) {
  for (let i = 0; i < items.length; i++) {
    heavyCalculation(items[i]);
  }
}

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5. Compliant Implementation Patterns (Good Examples)

TS (Periodic cooperative yielding to maintain input responsiveness):

async function processLargeArray(items: string[]) {
  for (let i = 0; i < items.length; i++) {
    heavyCalculation(items[i]);
    if (i % 50 === 0) {
      await (window.scheduler?.yield?.() ?? new Promise(r => setTimeout(r, 0)));
    }
  }
}

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6. How to Suppress (Ignore Directives)

If this pattern is required for an intentional exception, suppress the diagnostic using the canonical Charites Rule ID:

<!-- charites:ignore inp.unyielded-long-task intentional exception -->

// charites:ignore inp.unyielded-long-task intentional exception

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7. Configuration Reference (charites.yaml)

rules:
  inp.unyielded-long-task:
    severity: warn # error | warn | info | off

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8. Architectural Domain & Verification Reference

• Domain Architecture & Analysis Pipeline: See the inp Category Guide.
• 1-SSOT Golden Tri-Corpus Test Matrix: See the Verification Harness on the Master Home page.
• Rule Catalog Index: See Master Wiki Home.