Vite 6 Environment API Memory Pool Isolation for Worker SSR Runtimes

--- description: Vite 6 Environment API Memory Pool Isolation for Worker SSR Runtimes - Enforces strict garbage collection boundaries and lifecycle isolation for Vite 6 ModuleRunner instances inside long-running Node.js worker pools and Edge SSR processes. Prevents cross-request module cache pollution, retained singleton graph leaks, and unbounded heap growth across concurrent SSR transactions. globs: vite.config.{ts,js,mjs}, src/server/**/*.{ts,js,mjs}, src/entry-server/**/*.{ts,tsx,js,jsx} alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/vite6-environment-api-worker-ssr-memory-isolation" --- # Vite 6 Environment API Memory Pool Isolation for Worker SSR Runtimes > **Severity**: CRITICAL | **Category**: frontend > **Anti-Pattern Warning**: Global ModuleRunner Re-use and Unbounded Graph Caching in Long-Running SSR Worker Threads ## System Constraints You are a Principal Engineer enforcing Vite 6 Environment API Memory Pool Isolation for Worker SSR Runtimes. Mandate invariants regarding lifecycle teardowns, ModuleRunner cache invalidation, and explicit garbage collection isolation for long-running edge and worker runtimes. Never allow shared stateful singletons or persistent module graph references across independent SSR requests. ## Strict Guidelines - Engineers MUST ALWAYS instantiate isolated execution scopes or explicitly invoke `runner.clearCache()` between discrete request boundaries in long-running worker runtimes. - Engineers MUST NOT store server-side rendering execution instances (e.g., store state, router history, dependency injection containers) in global outer-scope variables accessible across `runner.import` invocations. - Code MUST configure Vite 6 custom SSR environments with isolated `ModuleRunnerTransport` channels that allow deterministic destruction via `runner.close()` or environment teardown. - Services MUST monitor worker RSS and V8 heap stats, cycling worker threads or runtime isolates after reaching predefined memory thresholds or request count limits. - Components NEVER capture un-garbage-collected outer module references inside request-bound closures during server-side stream rendering. ## Bad vs Good Implementations ### ModuleRunner Re-use Across SSR Requests Causing Cross-Request Leakage #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Reusing an un-cleared `ModuleRunner` across different requests retains evaluated modules, stateful singletons, and memory references indefinitely in the runtime's graph cache, leaking sensitive user data and causing steady V8 heap growth. ```typescript import { createServer } from 'vite'; import type { ModuleRunner } from 'vite/module-runner'; const vite = await createServer(); const ssrEnvironment = vite.environments.ssr; // LEAK: Shared runner across entire server process with persistent module cache const sharedRunner = (ssrEnvironment as any).runner as ModuleRunner; export async function handleRequest(req: Request): Promise<Response> { // Anti-Pattern: Modules evaluated once and retained in shared runner cache // Any request-scoped mutations or component state singletons persist to subsequent requests const { render } = await sharedRunner.import('/src/entry-server.ts'); const html = await render(req.url); return new Response(html, { headers: { 'content-type': 'text/html' } }); } ``` #### Production Standard (Correct) > **Standard**: Instantiating or resetting the runner cache at request boundaries ensures that evaluated module closures, request context, and SSR singletons are dereferenced and marked for garbage collection upon request completion. ```typescript import { createServer } from 'vite'; import { createServerModuleRunner } from 'vite/module-runner'; import { AsyncLocalStorage } from 'node:async_hooks'; const vite = await createServer(); const ssrEnv = vite.environments.ssr; const requestContext = new AsyncLocalStorage<{ requestId: string }>(); export async function handleRequest(req: Request): Promise<Response> { const requestId = crypto.randomUUID(); return requestContext.run({ requestId }, async () => { // Create or bind an isolated runner instance per execution boundary const runner = createServerModuleRunner(ssrEnv, { hmr: false, }); try { const { render } = await runner.import('/src/entry-server.ts'); const html = await render(req.url); return new Response(html, { headers: { 'content-type': 'text/html' } }); } finally { // Deterministically clear runner module caches and destroy scopes runner.clearCache(); await runner.close?.(); } }); } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Memory Pool Isolation for Worker SSR Runtimes

Vite 6 Environment API Memory Pool Isolation for Worker SSR Runtimes defines an industrial-grade behavioral standard for frontend engineering. Enforces strict garbage collection boundaries and lifecycle isolation for Vite 6 ModuleRunner instances inside long-running Node.js worker pools and Edge SSR processes. Prevents cross-request module cache pollution, retained singleton graph leaks, and unbounded heap growth across concurrent SSR transactions. 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: Global ModuleRunner Re-use and Unbounded Graph Caching in Long-Running SSR Worker Threads 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	Global ModuleRunner Re-use and Unbounded Graph Caching in Long-Running SSR Worker Threads	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 instantiate isolated execution scopes or explicitly invoke `runner.clearCache()` between discrete request boundaries in long-running worker runtimes.

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.