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frontendcritical PriorityID: vite6-environment-api-cross-runtime-isolation

Vite 6 Environment API Cross-Runtime Boundary and Global Isolation

Enforces strict boundary isolation and distinct module execution pipelines across heterogeneous runtimes (client, Node.js, workerd, Edge) using the Vite 6 Environment API. Prevents shared in-memory state, global namespace contamination (e.g., leaking Node.js process or Buffer into Edge/workerd), and cross-environment module graph leakage during multi-target development and SSR evaluation.

Prohibited Anti-Pattern: Cross-Runtime Scope Pollution and Shared In-Memory Module Graphs in Multi-Target Vite SSR

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---
description: Vite 6 Environment API Cross-Runtime Boundary and Global Isolation - Enforces strict boundary isolation and distinct module execution pipelines across heterogeneous runtimes (client, Node.js, workerd, Edge) using the Vite 6 Environment API. Prevents shared in-memory state, global namespace contamination (e.g., leaking Node.js process or Buffer into Edge/workerd), and cross-environment module graph leakage during multi-target development and SSR evaluation.
globs: vite.config.{ts,js,mjs}, src/**/*.{ts,tsx,js,jsx}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite6-environment-api-cross-runtime-isolation"
---

# Vite 6 Environment API Cross-Runtime Boundary and Global Isolation

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Cross-Runtime Scope Pollution and Shared In-Memory Module Graphs in Multi-Target Vite SSR

## System Constraints
You are a Principal Software Architect enforcing the Vite 6 Environment API isolation model. You mandate zero cross-runtime module graph leakage, isolated execution contexts, and strict scoping for Vite plugins targeting disparate runtime environments (e.g., Node.js SSR, Cloudflare workerd, Edge workers, and DOM client). Enforce distinct resolution conditions, separate ModuleRunner instances, and runtime-aware plugin hooks via `this.environment`.

## Strict Guidelines
- Engineers MUST ALWAYS configure runtime-specific resolution conditions via `environments.<name>.resolve.conditions` (e.g., ['node'] vs ['worker', 'workerd']) instead of relying on legacy root-level `ssr` config.
- Engineers MUST NOT share in-memory state, module caches, or global singletons between Vite environments within custom plugins or server middleware.
- Plugin hooks that manipulate code or resolve dependencies MUST ALWAYS verify `this.environment.name` before applying runtime-specific transformations or Node.js built-in polyfills.
- Services executing SSR code MUST utilize distinct `ModuleRunner` or environment-specific evaluators (such as `@cloudflare/vite-plugin` for workerd) rather than evaluating edge code in the Node.js main thread.
- Components and shared libraries NEVER access runtime-specific globals (`process.env`, `window`, `navigator`, `Buffer`, `caches`) without defensive gating or explicit environment injection.
- Engineers MUST configure isolated `define` replacements per environment to prevent leaking Node-specific build-time replacements into workerd/edge builds.

## Bad vs Good Implementations
### Vite 6 Multi-Environment Configuration Isolation

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Configuring SSR at the root with generic settings conflates Node.js SSR and Worker/Edge targets. Global definitions like `process.env` and unconditional transforms corrupt runtimes like workerd that enforce standard web primitives without Node built-in modules.
```typescript
import { defineConfig } from 'vite';

// BAD: Single legacy SSR target; leaks Node.js conditions and globals
// to edge/workerd targets, sharing the transform pipeline
export default defineConfig({
  ssr: {
    target: 'webworker',
    noExternal: true,
  },
  define: {
    'process.env.NODE_ENV': JSON.stringify('development'), // Leaks Node process global
  },
  plugins: [
    {
      name: 'api-injector',
      transform(code, id) {
        // Unconditionally injects Node APIs regardless of target environment
        return `import { Buffer } from 'node:buffer';\n${code}`;
      },
    },
  ],
});
```

#### Production Standard (Correct)
> **Standard**: Vite 6 Environment API cleanly separates `client`, `nodeSsr`, and `workerdSsr`. Resolution conditions are isolated, preventing invalid package imports, and plugin hooks check `this.environment.name` to avoid injecting Node-specific APIs into workers.
```typescript
import { defineConfig } from 'vite';

// GOOD: Vite 6 isolated environments with separate resolution conditions
export default defineConfig({
  environments: {
    client: {
      consumer: 'client',
      build: { outDir: 'dist/client' },
    },
    nodeSsr: {
      consumer: 'server',
      resolve: {
        conditions: ['node', 'import'],
        externalConditions: ['node', 'import'],
      },
      build: { outDir: 'dist/server' },
    },
    workerdSsr: {
      consumer: 'server',
      resolve: {
        conditions: ['workerd', 'worker', 'browser'],
        externalConditions: ['workerd', 'worker'],
      },
      build: { outDir: 'dist/edge' },
    },
  },
  plugins: [
    {
      name: 'api-injector',
      transform(code, id) {
        // Guard transformations using Vite 6 Environment context
        if (this.environment.name === 'nodeSsr') {
          return `import { Buffer } from 'node:buffer';\n${code}`;
        }
        return code;
      },
    },
  ],
});
```

### Isolated Environment Execution via ModuleRunner

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Using `vite.ssrLoadModule` runs code directly within the host Node.js runtime process, polluting `globalThis` and masking runtime discrepancies between Node and Edge/workerd primitives.
```typescript
import { createServer } from 'vite';

// BAD: Evaluating edge code directly in Node's ssrLoadModule
const vite = await createServer({
  server: { middlewareMode: true },
});

export async function handleRequest(url: string) {
  // ssrLoadModule evaluates in Node global scope, contaminating edge globals
  const { render } = await vite.ssrLoadModule('/src/entry.worker.ts');
  return render(url);
}
```

#### Production Standard (Correct)
> **Standard**: Vite 6 decouples evaluation from the Vite dev server using `createServerModuleRunner` bound specifically to `vite.environments.workerdSsr`. This guarantees that execution context, module cache, and global scopes remain fully isolated from the host Node server.
```typescript
import { createServer } from 'vite';
import { createServerModuleRunner } from 'vite/module-runner';

// GOOD: Vite 6 dedicated ModuleRunner linked to specific environment
const vite = await createServer({
  server: { middlewareMode: true },
});

const workerdEnv = vite.environments.workerdSsr;
const runner = createServerModuleRunner(workerdEnv, {
  // Supply runtime-specific transport evaluator or evaluator harness
  evaluator: workerdEnv.evaluator,
});

export async function handleRequest(url: string) {
  const { render } = await runner.import('/src/entry.worker.ts');
  return render(url);
}
```
Recommended MCP Servers (mcp-serverlist.com)

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

Cloudflare Wrangler MCP
Inspect and validate workerd runtime compliance and bindings locally.
Recommended Agent Skills (askills.dev)

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

Vite Environment Runner CLI
Validates multi-environment module graphs and verifies isolated resolution conditions in Vite 6.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Cross-Runtime Boundary and Global Isolation

Vite 6 Environment API Cross-Runtime Boundary and Global Isolation defines an industrial-grade behavioral standard for frontend engineering. Enforces strict boundary isolation and distinct module execution pipelines across heterogeneous runtimes (client, Node.js, workerd, Edge) using the Vite 6 Environment API. Prevents shared in-memory state, global namespace contamination (e.g., leaking Node.js process or Buffer into Edge/workerd), and cross-environment module graph leakage during multi-target development and SSR evaluation. 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: Cross-Runtime Scope Pollution and Shared In-Memory Module Graphs in Multi-Target Vite SSR 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 DriftCross-Runtime Scope Pollution and Shared In-Memory Module Graphs in Multi-Target Vite SSRCritical
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 runtime-specific resolution conditions via `environments.<name>.resolve.conditions` (e.g., ['node'] vs ['worker', 'workerd']) instead of relying on legacy root-level `ssr` config.

Engineers MUST ALWAYS configure runtime-specific resolution conditions via `environments.<name>.resolve.conditions` (e.g., ['node'] vs ['worker', 'workerd']) instead of relying on legacy root-level `ssr` config.

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 in-memory state, module caches, or global singletons between Vite environments within custom plugins or server middleware.

Engineers MUST NOT share in-memory state, module caches, or global singletons between Vite environments within custom plugins or server middleware.

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

Plugin hooks that manipulate code or resolve dependencies MUST ALWAYS verify `this.environment.name` before applying runtime-specific transformations or Node.js built-in polyfills.

Plugin hooks that manipulate code or resolve dependencies MUST ALWAYS verify `this.environment.name` before applying runtime-specific transformations or Node.js built-in 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.
4

Services executing SSR code MUST utilize distinct `ModuleRunner` or environment-specific evaluators (such as `@cloudflare/vite-plugin` for workerd) rather than evaluating edge code in the Node.js main thread.

Services executing SSR code MUST utilize distinct `ModuleRunner` or environment-specific evaluators (such as `@cloudflare/vite-plugin` for workerd) rather than evaluating edge code in the Node.js main thread.

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 and shared libraries NEVER access runtime-specific globals (`process.env`, `window`, `navigator`, `Buffer`, `caches`) without defensive gating or explicit environment injection.

Components and shared libraries NEVER access runtime-specific globals (`process.env`, `window`, `navigator`, `Buffer`, `caches`) without defensive gating or explicit environment injection.

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.
6

Engineers MUST configure isolated `define` replacements per environment to prevent leaking Node-specific build-time replacements into workerd/edge builds.

Engineers MUST configure isolated `define` replacements per environment to prevent leaking Node-specific build-time replacements into workerd/edge builds.

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 Cross-Runtime Boundary and Global Isolation critical for AI coding assistants?

Enforces strict boundary isolation and distinct module execution pipelines across heterogeneous runtimes (client, Node.js, workerd, Edge) using the Vite 6 Environment API. Prevents shared in-memory state, global namespace contamination (e.g., leaking Node.js process or Buffer into Edge/workerd), and cross-environment module graph leakage during multi-target development and SSR evaluation. 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 (Cross-Runtime Scope Pollution and Shared In-Memory Module Graphs in Multi-Target Vite SSR) 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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