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frontendcritical PriorityID: vite-6-environment-api-worker-runtime-isolation

Vite 6 Environment API Worker-Runtime Context Isolation Standard

Enforces strict runtime module isolation and global scope compartmentalization between client, Node SSR, and Edge/Worker execution environments using Vite 6's Environment API. Prevents cross-environment prototype pollution, global scope bleed, and single-module-graph invalidation bugs during unified full-stack HMR and production bundling passes.

Prohibited Anti-Pattern: Global Scope Bleed and Shared Module Graph Pollution Across Heterogeneous Runtimes

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---
description: Vite 6 Environment API Worker-Runtime Context Isolation Standard - Enforces strict runtime module isolation and global scope compartmentalization between client, Node SSR, and Edge/Worker execution environments using Vite 6's Environment API. Prevents cross-environment prototype pollution, global scope bleed, and single-module-graph invalidation bugs during unified full-stack HMR and production bundling passes.
globs: vite.config.{ts,js,mjs}, src/**/*.{ts,tsx,js,jsx}, server/**/*.{ts,js,mjs}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite-6-environment-api-worker-runtime-isolation"
---

# Vite 6 Environment API Worker-Runtime Context Isolation Standard

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Global Scope Bleed and Shared Module Graph Pollution Across Heterogeneous Runtimes

## System Constraints
You are a Principal Architect enforcing the Vite 6 Environment API Worker-Runtime Context Isolation Standard. Vite 6 decouples the dev server and module runner into discrete Environment instances (e.g., 'client', 'ssr', 'workerd'). You must ensure that code targets isolated module runner runtimes, that plugins configure environment-specific hooks instead of generic transforms, and that global state is never shared across heterogeneous execution contexts during HMR or bundle generation.

## Strict Guidelines
- Engineers MUST ALWAYS configure environment instances using the Vite 6 `environments` record (e.g., `client`, `ssr`, custom runtimes) rather than legacy dual-pass CLI invocations or ad-hoc SSR flags.
- Engineers MUST NOT access ambient runtime globals (like `window`, `process.env`, or `navigator`) outside their respective execution target without explicit environment conditional guards or environment-scoped polyfills.
- Vite plugins MUST implement environment-aware hooks via `this.environment` (e.g., `this.environment.name === 'ssr'`) rather than relying on legacy hook options like `ssr: boolean`.
- Custom worker runtimes (e.g., Cloudflare Workerd, V8 isolates) MUST instantiate a dedicated `ModuleRunner` with an explicit `FetchableDevEnvironment` transport to maintain deterministic isolation from the Node dev server host.
- Engineers MUST NEVER share singletons or module-level mutable variables across client and SSR execution graphs during development HMR cycles.

## Bad vs Good Implementations
### Vite 6 Environment API Multi-Runtime Server Configuration

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Relies on legacy process environment flags and the deprecated ssr boolean option in transform hooks, causing global state leakage, cross-environment compilation race conditions, and failing to utilize discrete module graphs provided by Vite 6.
```typescript
import { defineConfig } from 'vite';

// Legacy Vite 5 dual-target configuration anti-pattern
export default defineConfig({
  build: {
    ssr: process.env.IS_SSR ? 'src/entry-server.ts' : false,
    outDir: process.env.IS_SSR ? 'dist/server' : 'dist/client',
  },
  ssr: {
    target: 'webworker',
    noExternal: true,
  },
  plugins: [
    {
      name: 'leaky-plugin',
      transform(code, id, options) {
        // Legacy boolean check leaks ambient build context
        if (options?.ssr) {
          return code.replace('__RUNTIME__', '"server"');
        }
        return code.replace('__RUNTIME__', '"client"');
      }
    }
  ]
});
```

#### Production Standard (Correct)
> **Standard**: Leverages Vite 6's first-class `environments` API to partition client, Node SSR, and Edge runtimes into independent environments with discrete resolver conditions, build targets, and environment-scoped plugin hooks via `this.environment.name`.
```typescript
import { defineConfig } from 'vite';

export default defineConfig({
  environments: {
    client: {
      build: {
        outDir: 'dist/client',
        rollupOptions: {
          input: 'src/entry-client.ts',
        },
      },
    },
    ssr: {
      build: {
        outDir: 'dist/server',
        rollupOptions: {
          input: 'src/entry-server.ts',
        },
      },
      resolve: {
        conditions: ['node', 'import'],
        noExternal: true,
      },
    },
    edge: {
      dev: {
        createEnvironment(name, config) {
          // Discrete execution runtime with dedicated transport
          return new (require('vite').DevEnvironment)(name, config);
        },
      },
      resolve: {
        conditions: ['worker', 'workerd'],
      },
    },
  },
  plugins: [
    {
      name: 'isolated-plugin',
      // Environment-specific hook execution via Vite 6 hook dispatch
      transform: {
        order: 'pre',
        handler(code, id) {
          const envName = this.environment.name;
          return code.replace('__RUNTIME__', JSON.stringify(envName));
        },
      },
    },
  ],
});
```

### Isolated Dev ModuleRunner Consumer for Non-Node Execution Runtimes

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: `ssrLoadModule` runs code directly within the Node.js host process using Node's module loader, contaminating edge code with Node.js built-ins and failing to isolate worker context globals.
```typescript
import { createServer } from 'vite';

const server = await createServer();
// Leaks Node globals into simulated worker context
const { render } = await server.ssrLoadModule('/src/entry-edge.ts');
export async function handleRequest(req: Request) {
  return render(req);
}
```

#### Production Standard (Correct)
> **Standard**: Employs Vite 6 `ModuleRunner` decoupled via an explicit communication transport (`edgeEnvironment.hot`) and discrete evaluator, preventing Node host pollution and guaranteeing isolated worker runtime execution semantics.
```typescript
import { createServer } from 'vite';
import { ModuleRunner, ESModulesEvaluator } from 'vite/module-runner';

const server = await createServer();
const edgeEnvironment = server.environments.edge;

// ModuleRunner communicates with the Vite dev server via isolated transport
const runner = new ModuleRunner(
  {
    root: server.config.root,
    transport: edgeEnvironment.hot,
  },
  new ESModulesEvaluator()
);

const { render } = await runner.import('/src/entry-edge.ts');

export async function handleRequest(req: Request) {
  return render(req);
}
```
Recommended MCP Servers (mcp-serverlist.com)

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

Vite Dev Context MCP
Inspects running Vite 6 Environment API instances, module graphs, and runtime runner contexts.
Recommended Agent Skills (askills.dev)

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

Verify Vite Environments
Validates plugin compatibility and isolated module graph resolution against Vite 6 Environment APIs.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Worker-Runtime Context Isolation Standard

Vite 6 Environment API Worker-Runtime Context Isolation Standard defines an industrial-grade behavioral standard for frontend engineering. Enforces strict runtime module isolation and global scope compartmentalization between client, Node SSR, and Edge/Worker execution environments using Vite 6's Environment API. Prevents cross-environment prototype pollution, global scope bleed, and single-module-graph invalidation bugs during unified full-stack HMR and production bundling passes. 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 Bleed and Shared Module Graph Pollution Across Heterogeneous Runtimes 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 Bleed and Shared Module Graph Pollution Across Heterogeneous RuntimesCritical
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 environment instances using the Vite 6 `environments` record (e.g., `client`, `ssr`, custom runtimes) rather than legacy dual-pass CLI invocations or ad-hoc SSR flags.

Engineers MUST ALWAYS configure environment instances using the Vite 6 `environments` record (e.g., `client`, `ssr`, custom runtimes) rather than legacy dual-pass CLI invocations or ad-hoc 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 access ambient runtime globals (like `window`, `process.env`, or `navigator`) outside their respective execution target without explicit environment conditional guards or environment-scoped polyfills.

Engineers MUST NOT access ambient runtime globals (like `window`, `process.env`, or `navigator`) outside their respective execution target without explicit environment conditional guards or environment-scoped polyfills.

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

Vite plugins MUST implement environment-aware hooks via `this.environment` (e.g., `this.environment.name === 'ssr'`) rather than relying on legacy hook options like `ssr

Vite plugins MUST implement environment-aware hooks via `this.environment` (e.g., `this.environment.name === 'ssr'`) rather than relying on legacy hook options like `ssr: boolean`.

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

Custom worker runtimes (e.g., Cloudflare Workerd, V8 isolates) MUST instantiate a dedicated `ModuleRunner` with an explicit `FetchableDevEnvironment` transport to maintain deterministic isolation from the Node dev server host.

Custom worker runtimes (e.g., Cloudflare Workerd, V8 isolates) MUST instantiate a dedicated `ModuleRunner` with an explicit `FetchableDevEnvironment` transport to maintain deterministic isolation from the Node dev server host.

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

Engineers MUST NEVER share singletons or module-level mutable variables across client and SSR execution graphs during development HMR cycles.

Engineers MUST NEVER share singletons or module-level mutable variables across client and SSR execution graphs during development HMR cycles.

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 Worker-Runtime Context Isolation Standard critical for AI coding assistants?

Enforces strict runtime module isolation and global scope compartmentalization between client, Node SSR, and Edge/Worker execution environments using Vite 6's Environment API. Prevents cross-environment prototype pollution, global scope bleed, and single-module-graph invalidation bugs during unified full-stack HMR and production bundling passes. 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 Bleed and Shared Module Graph Pollution Across Heterogeneous Runtimes) 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

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