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frontendcritical PriorityID: vite-6-environment-runtime-isolation-boundary-standard

Vite 6 Environment API Runtime Isolation and Prototype Boundary Guardrail

Enforces strict runtime boundary isolation when configuring multi-environment applications using Vite 6's Environment API and ModuleRunner. Prevents cross-target global scope pollution, host-level prototype mutation, and shared module cache contamination across heterogeneous SSR runtimes (Node.js, Edge/Workerd, Browser micro-frontends).

Prohibited Anti-Pattern: Global Scope Mutation and Cross-Environment Prototype Contamination via Unisolated Vite 6 Module Runners

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---
description: Vite 6 Environment API Runtime Isolation and Prototype Boundary Guardrail - Enforces strict runtime boundary isolation when configuring multi-environment applications using Vite 6's Environment API and ModuleRunner. Prevents cross-target global scope pollution, host-level prototype mutation, and shared module cache contamination across heterogeneous SSR runtimes (Node.js, Edge/Workerd, Browser micro-frontends).
globs: vite.config.{ts,js,mjs}, src/**/*.{ts,tsx}, server/**/*.{ts,js,mjs}, packages/**/vite.config.{ts,js,mjs}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite-6-environment-runtime-isolation-boundary-standard"
---

# Vite 6 Environment API Runtime Isolation and Prototype Boundary Guardrail

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Global Scope Mutation and Cross-Environment Prototype Contamination via Unisolated Vite 6 Module Runners

## System Constraints
You are a Principal Software Architect enforcing runtime isolation boundaries using the Vite 6 Environment API. You must reject any configuration or runtime code that leaks shared memory, pollutes host `globalThis`, uses deprecated `ssrLoadModule` across heterogeneous targets, or bypasses dedicated `ModuleRunner` evaluators.

## Strict Guidelines
- Engineers MUST ALWAYS configure distinct environments (e.g., `client`, `ssr`, `edge`) in `vite.config.ts` via the top-level `environments` property instead of relying on legacy monolithic root SSR flags.
- Engineers MUST NOT share `ModuleEvaluator` instances or module caches across distinct SSR worker targets or micro-frontend hosts.
- Engineers MUST use `environment.runner.importByUrl` or an isolated `ModuleRunner` instead of deprecated `viteServer.ssrLoadModule` or shared node execution contexts.
- Code executed inside an edge or worker environment MUST NEVER mutate host-native prototypes (`Object.prototype`, `Array.prototype`, `Promise.prototype`) or assign un-namespaced variables to `globalThis`.
- Services running heterogeneous micro-frontends MUST instantiate isolated `DevEnvironment` containers with strict transport boundaries (`RunnerTransport`) to prevent memory leaks and state retention across requests.

## Bad vs Good Implementations
### Migrate from Deprecated ssrLoadModule with Leaky Globals to Vite 6 Environment ModuleRunner

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Using legacy `ssrLoadModule` evaluates SSR bundles in the root Node.js process context without boundary isolation. Mutating `globalThis` or `Object.prototype` directly bleeds polyfills and side effects into all client/edge worker compilations sharing the Vite dev server.
```typescript
import { createServer } from 'vite';

const vite = await createServer({
  server: { middlewareMode: true },
  appType: 'custom'
});

// Anti-pattern: Mutating global process/window across all environments
(globalThis as any).POLYFILLED_EDGE_TARGET = true;
Object.prototype['__leakedTelemetry'] = () => 'polluted';

export async function handleRequest(url: string) {
  // Anti-pattern: Legacy ssrLoadModule executes inside the host Node.js process without runtime sandboxing
  const entry = await vite.ssrLoadModule('/src/entry.server.ts');
  return entry.render(url);
}
```

#### Production Standard (Correct)
> **Standard**: Declares explicit environment configurations (`client`, `ssr`, `edge`) in Vite 6, using dedicated `DevEnvironment.runner` instances. Each environment guarantees isolated dependency resolution and avoids prototype pollution across heterogeneous runtime boundaries.
```typescript
import { createServer, DevEnvironment } from 'vite';
import { ModuleRunner, ESModulesEvaluator } from 'vite/module-runner';

const vite = await createServer({
  appType: 'custom',
  environments: {
    client: {
      build: { outDir: 'dist/client' }
    },
    ssr: {
      build: { outDir: 'dist/ssr' },
      resolve: { conditions: ['node', 'import'] }
    },
    edge: {
      build: { outDir: 'dist/edge' },
      resolve: { conditions: ['workerd', 'worker'] }
    }
  }
});

export async function handleIsolatedRequest(envName: 'ssr' | 'edge', url: string) {
  const env = vite.environments[envName] as DevEnvironment;
  if (!env || !('runner' in env)) {
    throw new Error(`Target environment '${envName}' is not a runnable DevEnvironment.`);
  }

  // Production invariant: Evaluate through dedicated Environment ModuleRunner
  const entry = await env.runner.importByUrl('/src/entry.' + envName + '.ts');
  return entry.render(url);
}
```
Recommended MCP Servers (mcp-serverlist.com)

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

Vite Runtime Inspector MCP
Inspects Vite 6 ModuleRunner graphs, environments, and active transform pipelines for runtime boundary violations.
Recommended Agent Skills (askills.dev)

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

Vite Environment Audit CLI
Analyzes vite.config.ts and worker runtimes to verify zero cross-environment prototype pollution and ensure valid Environment API usage.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Runtime Isolation and Prototype Boundary Guardrail

Vite 6 Environment API Runtime Isolation and Prototype Boundary Guardrail defines an industrial-grade behavioral standard for frontend engineering. Enforces strict runtime boundary isolation when configuring multi-environment applications using Vite 6's Environment API and ModuleRunner. Prevents cross-target global scope pollution, host-level prototype mutation, and shared module cache contamination across heterogeneous SSR runtimes (Node.js, Edge/Workerd, Browser micro-frontends). 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 Scope Mutation and Cross-Environment Prototype Contamination via Unisolated Vite 6 Module Runners 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 DriftGlobal Scope Mutation and Cross-Environment Prototype Contamination via Unisolated Vite 6 Module RunnersCritical
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 configure distinct environments (e.g., `client`, `ssr`, `edge`) in `vite.config.ts` via the top-level `environments` property instead of relying on legacy monolithic root SSR flags.

Engineers MUST ALWAYS configure distinct environments (e.g., `client`, `ssr`, `edge`) in `vite.config.ts` via the top-level `environments` property instead of relying on legacy monolithic root SSR flags.

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 share `ModuleEvaluator` instances or module caches across distinct SSR worker targets or micro-frontend hosts.

Engineers MUST NOT share `ModuleEvaluator` instances or module caches across distinct SSR worker targets or micro-frontend hosts.

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

Engineers MUST use `environment.runner.importByUrl` or an isolated `ModuleRunner` instead of deprecated `viteServer.ssrLoadModule` or shared node execution contexts.

Engineers MUST use `environment.runner.importByUrl` or an isolated `ModuleRunner` instead of deprecated `viteServer.ssrLoadModule` or shared node execution contexts.

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

Code executed inside an edge or worker environment MUST NEVER mutate host-native prototypes (`Object.prototype`, `Array.prototype`, `Promise.prototype`) or assign un-namespaced variables to `globalThis`.

Code executed inside an edge or worker environment MUST NEVER mutate host-native prototypes (`Object.prototype`, `Array.prototype`, `Promise.prototype`) or assign un-namespaced variables to `globalThis`.

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

Services running heterogeneous micro-frontends MUST instantiate isolated `DevEnvironment` containers with strict transport boundaries (`RunnerTransport`) to prevent memory leaks and state retention across requests.

Services running heterogeneous micro-frontends MUST instantiate isolated `DevEnvironment` containers with strict transport boundaries (`RunnerTransport`) to prevent memory leaks and state retention across requests.

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 Vite 6 Environment API Runtime Isolation and Prototype Boundary Guardrail critical for AI coding assistants?

Enforces strict runtime boundary isolation when configuring multi-environment applications using Vite 6's Environment API and ModuleRunner. Prevents cross-target global scope pollution, host-level prototype mutation, and shared module cache contamination across heterogeneous SSR runtimes (Node.js, Edge/Workerd, Browser micro-frontends). 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 (Global Scope Mutation and Cross-Environment Prototype Contamination via Unisolated Vite 6 Module Runners) 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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Citation & Open Source Attribution Guidelines

This specification is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0). You are completely free to adapt and share this rule in your workspace. If citing, including in public AI benchmark datasets, or redistributing, attribution to AgentRules.org is required.

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