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

Vite 6 Environment API Multi-Runtime Module Isolation Boundary

Vite 6 replaces legacy monolithic SSR handling with the Environment API, enabling independent module graphs, runner pipelines, and transform contexts across heterogeneous runtimes (Node.js, workerd, Edge, browser). This guardrail strictly enforces execution context isolation, per-environment resolution conditions, and scoped plugin lifecycle hooks to prevent catastrophic module leakage, invalid native bindings, and cross-runtime graph contamination.

Prohibited Anti-Pattern: Leaking Node Built-ins and Cross-Polluting Module Graphs Across Vite 6 Environments

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---
description: Vite 6 Environment API Multi-Runtime Module Isolation Boundary - Vite 6 replaces legacy monolithic SSR handling with the Environment API, enabling independent module graphs, runner pipelines, and transform contexts across heterogeneous runtimes (Node.js, workerd, Edge, browser). This guardrail strictly enforces execution context isolation, per-environment resolution conditions, and scoped plugin lifecycle hooks to prevent catastrophic module leakage, invalid native bindings, and cross-runtime graph contamination.
globs: vite.config.ts, vite.config.*.ts, src/**/*.{ts,tsx}, plugins/**/*.ts
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite6-environment-api-runtime-isolation-boundary"
---

# Vite 6 Environment API Multi-Runtime Module Isolation Boundary

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Leaking Node Built-ins and Cross-Polluting Module Graphs Across Vite 6 Environments

## System Constraints
You are a Principal Software Architect enforcing runtime boundary integrity under Vite 6's Environment API. You must ensure that plugins, resolution conditions, module graphs, and runner instances remain strictly isolated across browser, Node.js, and edge (workerd) environments without state leakage or invalid cross-runtime imports.

## Strict Guidelines
- Engineers MUST configure distinct runtime boundaries under the Vite 6 `environments` configuration block rather than relying on legacy monolithic root-level `ssr` flags.
- Engineers MUST specify explicit `resolve.conditions` per environment (e.g., `['workerd', 'worker']` for Cloudflare Workers vs `['node']` for server instances) to prevent runtime-incompatible package exports from resolving.
- Plugins targeting specific compilation targets MUST check `this.environment.name` in hook execution (e.g., `resolveId`, `transform`, `load`) or define `applyToEnvironment(env)` to prevent execution in incompatible runtime graphs.
- Engineers MUST NOT share stateful transform caches, singletons, or module caches across distinct `DevEnvironment` instances.
- Module runner implementations MUST use isolated `ModuleRunner` instances with explicit `runner.transport` bindings corresponding strictly to their designated target environment.
- Components and application code MUST NEVER import Node.js native primitives (`node:fs`, `node:path`, `node:async_hooks`) in files reachable by the `client` or `edge`/`workerd` module graphs.

## Bad vs Good Implementations
### Vite 6 Environment API Multi-Runtime Configuration and Plugin Scoping

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: This configuration uses legacy Vite SSR options and an unscoped plugin. The plugin transform hook runs globally across all compilation targets without checking `this.environment.name`, polluting the shared cache across runtimes and dangerously leaking host Node.js environment secrets into edge or browser bundles.
```typescript
import { defineConfig, type Plugin } from 'vite';

// ANTI-PATTERN: Shared global state and unscoped hook transforms
const sharedTransformCache = new Map<string, string>();

function badRuntimePlugin(): Plugin {
  return {
    name: 'bad-runtime-plugin',
    transform(code, id) {
      // Fails to check this.environment - executes across client, workerd, and node
      if (code.includes('process.env.SECRET_KEY')) {
        // Unsafe leakage of node-specific globals into client or edge bundles
        return code.replace('process.env.SECRET_KEY', JSON.stringify(process.env.SECRET_KEY));
      }
      sharedTransformCache.set(id, code);
      return null;
    }
  };
}

export default defineConfig({
  // Legacy SSR configuration mixed with edge requirements
  ssr: {
    target: 'webworker',
    noExternal: true
  },
  plugins: [badRuntimePlugin()]
});
```

#### Production Standard (Correct)
> **Standard**: Leverages the Vite 6 Environment API with strictly partitioned environments (`client`, `ssr`, and `edge`). Resolution conditions ensure `workerd` packages resolve correctly for edge compilation, and the plugin uses `applyToEnvironment` and `this.environment.name` to enforce compile-time isolation boundaries against illegal Node.js runtime imports.
```typescript
import { defineConfig, type Plugin, type DevEnvironment } from 'vite';

function edgeRuntimeGuardPlugin(): Plugin {
  return {
    name: 'edge-runtime-guard',
    // Enforce hook isolation by scoping exclusively to non-client environments
    applyToEnvironment(environment: DevEnvironment) {
      return environment.name === 'edge' || environment.name === 'ssr';
    },
    resolveId(source) {
      // Enforce strict runtime module isolation
      if (this.environment.name === 'edge' && source.startsWith('node:')) {
        throw new Error(
          `[vite-env-boundary] Prohibited Node built-in '${source}' imported in '${this.environment.name}' environment graph.`
        );
      }
      return null;
    }
  };
}

export default defineConfig({
  environments: {
    client: {
      consumer: 'client',
      build: {
        outDir: 'dist/client'
      }
    },
    ssr: {
      consumer: 'server',
      resolve: {
        conditions: ['node', 'import']
      },
      build: {
        outDir: 'dist/ssr',
        target: 'node22'
      }
    },
    edge: {
      consumer: 'server',
      resolve: {
        conditions: ['workerd', 'worker', 'browser'],
        noExternal: true
      },
      build: {
        outDir: 'dist/edge',
        target: 'esnext'
      }
    }
  },
  plugins: [edgeRuntimeGuardPlugin()]
});
```
Recommended MCP Servers (mcp-serverlist.com)

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

AST & Module Graph Inspector
Analyzes AST dependencies and imports to verify environmental module boundary compliance prior to build execution.
Recommended Agent Skills (askills.dev)

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

Vite 6 Environment Configuration Validator
CLI tool to validate Vite 6 config files against multi-environment isolation and export condition rules.
Architectural Specification & Invariant Rationale

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

Vite 6 Environment API Multi-Runtime Module Isolation Boundary defines an industrial-grade behavioral standard for frontend engineering. Vite 6 replaces legacy monolithic SSR handling with the Environment API, enabling independent module graphs, runner pipelines, and transform contexts across heterogeneous runtimes (Node.js, workerd, Edge, browser). This guardrail strictly enforces execution context isolation, per-environment resolution conditions, and scoped plugin lifecycle hooks to prevent catastrophic module leakage, invalid native bindings, and cross-runtime graph contamination. 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: Leaking Node Built-ins and Cross-Polluting Module Graphs Across Vite 6 Environments 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 DriftLeaking Node Built-ins and Cross-Polluting Module Graphs Across Vite 6 EnvironmentsCritical
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 configure distinct runtime boundaries under the Vite 6 `environments` configuration block rather than relying on legacy monolithic root-level `ssr` flags.

Engineers MUST configure distinct runtime boundaries under the Vite 6 `environments` configuration block rather than relying on legacy monolithic root-level `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 specify explicit `resolve.conditions` per environment (e.g., `['workerd', 'worker']` for Cloudflare Workers vs `['node']` for server instances) to prevent runtime-incompatible package exports from resolving.

Engineers MUST specify explicit `resolve.conditions` per environment (e.g., `['workerd', 'worker']` for Cloudflare Workers vs `['node']` for server instances) to prevent runtime-incompatible package exports from resolving.

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

Plugins targeting specific compilation targets MUST check `this.environment.name` in hook execution (e.g., `resolveId`, `transform`, `load`) or define `applyToEnvironment(env)` to prevent execution in incompatible runtime graphs.

Plugins targeting specific compilation targets MUST check `this.environment.name` in hook execution (e.g., `resolveId`, `transform`, `load`) or define `applyToEnvironment(env)` to prevent execution in incompatible runtime 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.
4

Engineers MUST NOT share stateful transform caches, singletons, or module caches across distinct `DevEnvironment` instances.

Engineers MUST NOT share stateful transform caches, singletons, or module caches across distinct `DevEnvironment` instances.

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

Module runner implementations MUST use isolated `ModuleRunner` instances with explicit `runner.transport` bindings corresponding strictly to their designated target environment.

Module runner implementations MUST use isolated `ModuleRunner` instances with explicit `runner.transport` bindings corresponding strictly to their designated target environment.

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

Components and application code MUST NEVER import Node.js native primitives (`node

Components and application code MUST NEVER import Node.js native primitives (`node:fs`, `node:path`, `node:async_hooks`) in files reachable by the `client` or `edge`/`workerd` 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.
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 Isolation Boundary critical for AI coding assistants?

Vite 6 replaces legacy monolithic SSR handling with the Environment API, enabling independent module graphs, runner pipelines, and transform contexts across heterogeneous runtimes (Node.js, workerd, Edge, browser). This guardrail strictly enforces execution context isolation, per-environment resolution conditions, and scoped plugin lifecycle hooks to prevent catastrophic module leakage, invalid native bindings, and cross-runtime graph contamination. 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 (Leaking Node Built-ins and Cross-Polluting Module Graphs Across Vite 6 Environments) 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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