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

Vite 6 Environment API Multi-Runtime Module Scope Boundary Enforcement

Enforces strict isolation of module resolution graphs and global scope boundaries across Vite 6 client, edge worker, and Node.js SSR environments. Prevents cross-runtime polyfill pollution, leaking Node.js built-ins into Web Worker/Edge environments, and accidental cross-contamination of client bundles with SSR dependencies.

Prohibited Anti-Pattern: Cross-Environment Module Graph Bleed and Ambient Global Polyfill Contamination

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---
description: Vite 6 Environment API Multi-Runtime Module Scope Boundary Enforcement - Enforces strict isolation of module resolution graphs and global scope boundaries across Vite 6 client, edge worker, and Node.js SSR environments. Prevents cross-runtime polyfill pollution, leaking Node.js built-ins into Web Worker/Edge environments, and accidental cross-contamination of client bundles with SSR dependencies.
globs: vite.config.{ts,js,mjs}, src/**/*.{ts,tsx,js,jsx}, server/**/*.{ts,js}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite-6-environment-api-runtime-scope-isolation"
---

# Vite 6 Environment API Multi-Runtime Module Scope Boundary Enforcement

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Cross-Environment Module Graph Bleed and Ambient Global Polyfill Contamination

## System Constraints
You are a Principal Software Architect enforcing Vite 6 Environment API multi-runtime isolation boundaries. In Vite 6, each compilation target (client, server, edge) MUST operate as a completely detached Environment with dedicated ModuleGraph, optimizeDeps, and resolve configurations. You must prevent ambient polyfill leaks (e.g., node:crypto polyfilling globally), ensure runtime-specific package exports conditions are honored via resolve.conditions, and verify that shared code never relies on implicit environment-specific globals without explicit runtime branching or dedicated runner abstraction boundaries.

## Strict Guidelines
- Engineers MUST ALWAYS configure distinct environments (e.g., `client`, `ssr`, `edge`) via the `environments` block in Vite 6 instead of legacy boolean flags or unified rollup options.
- Engineers MUST NOT rely on ambient runtime polyfills (such as `process`, `Buffer`, or `global`) injected at the root config level that pollute Edge or Client module graphs.
- Engineers MUST declare dedicated `resolve.conditions` and `resolve.noExternal` for each environment independently to reflect Node vs Workerd/Edge vs Browser export paths.
- Plugins MUST target specific environments using `this.environment.name` or `applyToEnvironment(env)` rather than executing universally across all compilation passes.
- Shared cross-runtime libraries MUST isolate ambient global access behind explicit runtime capability checks or dependency injection tokens rather than top-level global reads.

## Bad vs Good Implementations
### Vite 6 Multi-Environment Definition with Strict Module Isolation

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Declaring globals and resolution conditions at the root causes polyfill pollution across targets: client code imports Node shims, while Edge runtimes crash on browser-specific polyfills like 'window'.
```typescript
import { defineConfig } from 'vite';

// Anti-pattern: Unified config attempting to handle SSR and Client with global defines
export default defineConfig({
  define: {
    'process.env.NODE_ENV': JSON.stringify('production'),
    global: 'window' // Contaminates SSR & Edge worker passes with window references
  },
  resolve: {
    // Ambient conditions shared across both Node SSR and browser client
    conditions: ['node', 'browser', 'workerd']
  },
  build: {
    ssr: true // Legacy monolithic SSR toggle without isolated environment scope
  }
});
```

#### Production Standard (Correct)
> **Standard**: Explicitly declares discrete Vite 6 environments with isolated export resolution conditions, strictly separating package resolution paths between Client, Node SSR, and Edge runtimes.
```typescript
import { defineConfig } from 'vite';

export default defineConfig({
  environments: {
    client: {
      build: {
        outDir: 'dist/client'
      },
      resolve: {
        conditions: ['browser', 'module']
      }
    },
    ssr: {
      build: {
        outDir: 'dist/ssr',
        ssr: true
      },
      resolve: {
        conditions: ['node', 'import']
      }
    },
    edge: {
      build: {
        outDir: 'dist/edge'
      },
      resolve: {
        conditions: ['workerd', 'worker', 'edge-routine']
      }
    }
  }
});
```

### Environment-Aware Plugin Guarding Against Cross-Runtime Execution

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: The plugin indiscriminately executes across every module graph pass, leaking heavy Node.js polyfills into the Edge Worker and Client bundles.
```typescript
import type { Plugin } from 'vite';

// Anti-pattern: Plugin transforms code in all environments indiscriminately
export function nodePolyfillPlugin(): Plugin {
  return {
    name: 'node-polyfill-injector',
    transform(code, id) {
      // Injects Node polyfills into every file regardless of whether it's Edge or Browser
      if (id.endsWith('.ts')) {
        return `import { Buffer } from 'buffer';\n${code}`;
      }
      return null;
    }
  };
}
```

#### Production Standard (Correct)
> **Standard**: Uses Vite 6 `applyToEnvironment` hook and `this.environment.name` check to ensure transforms apply only within the target runtime module graph.
```typescript
import type { Plugin } from 'vite';

export function nodePolyfillPlugin(): Plugin {
  return {
    name: 'node-polyfill-injector',
    applyToEnvironment(environment) {
      // Strictly restricts plugin execution to the Node SSR environment pass
      return environment.name === 'ssr';
    },
    transform(code, id) {
      if (this.environment.name === 'ssr' && id.endsWith('.ts')) {
        return {
          code: `import { Buffer } from 'node:buffer';\n${code}`,
          map: null
        };
      }
      return null;
    }
  };
}
```
Recommended MCP Servers (mcp-serverlist.com)

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

Vite Ecosystem Inspector MCP
Inspects Vite runtime configurations, module graphs, and multi-environment resolve parameters.
Recommended Agent Skills (askills.dev)

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

Bundle Runtime Environment Auditor
Validates export conditions and module graph boundaries across build environments to prevent cross-contamination.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Multi-Runtime Module Scope Boundary Enforcement

Vite 6 Environment API Multi-Runtime Module Scope Boundary Enforcement defines an industrial-grade behavioral standard for frontend engineering. Enforces strict isolation of module resolution graphs and global scope boundaries across Vite 6 client, edge worker, and Node.js SSR environments. Prevents cross-runtime polyfill pollution, leaking Node.js built-ins into Web Worker/Edge environments, and accidental cross-contamination of client bundles with SSR dependencies. 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-Environment Module Graph Bleed and Ambient Global Polyfill Contamination 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-Environment Module Graph Bleed and Ambient Global Polyfill ContaminationCritical
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`) via the `environments` block in Vite 6 instead of legacy boolean flags or unified rollup options.

Engineers MUST ALWAYS configure distinct environments (e.g., `client`, `ssr`, `edge`) via the `environments` block in Vite 6 instead of legacy boolean flags or unified rollup options.

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 rely on ambient runtime polyfills (such as `process`, `Buffer`, or `global`) injected at the root config level that pollute Edge or Client module graphs.

Engineers MUST NOT rely on ambient runtime polyfills (such as `process`, `Buffer`, or `global`) injected at the root config level that pollute Edge or Client module graphs.

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 declare dedicated `resolve.conditions` and `resolve.noExternal` for each environment independently to reflect Node vs Workerd/Edge vs Browser export paths.

Engineers MUST declare dedicated `resolve.conditions` and `resolve.noExternal` for each environment independently to reflect Node vs Workerd/Edge vs Browser export paths.

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

Plugins MUST target specific environments using `this.environment.name` or `applyToEnvironment(env)` rather than executing universally across all compilation passes.

Plugins MUST target specific environments using `this.environment.name` or `applyToEnvironment(env)` rather than executing universally across all compilation passes.

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

Shared cross-runtime libraries MUST isolate ambient global access behind explicit runtime capability checks or dependency injection tokens rather than top-level global reads.

Shared cross-runtime libraries MUST isolate ambient global access behind explicit runtime capability checks or dependency injection tokens rather than top-level global reads.

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 Multi-Runtime Module Scope Boundary Enforcement critical for AI coding assistants?

Enforces strict isolation of module resolution graphs and global scope boundaries across Vite 6 client, edge worker, and Node.js SSR environments. Prevents cross-runtime polyfill pollution, leaking Node.js built-ins into Web Worker/Edge environments, and accidental cross-contamination of client bundles with SSR dependencies. 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-Environment Module Graph Bleed and Ambient Global Polyfill Contamination) 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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