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frontendcritical PriorityID: vite6-environment-api-runtime-isolation-vite-6-environme-469

Vite 6 Environment API Cross-Runtime Module Isolation Barrier

Enforces strict physical isolation between client, server, and worker module graphs using the Vite 6 Environment API. Prevents runtime pollution, invalid cross-environment imports (such as Node.js built-ins leaking into edge or browser bundles), and shared mutable plugin state across compilation environments during multi-environment SSR builds.

Prohibited Anti-Pattern: Cross-Runtime Module Graph Contamination via Legacy SSR Flags and Shared Plugin State

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---
description: Vite 6 Environment API Cross-Runtime Module Isolation Barrier - Enforces strict physical isolation between client, server, and worker module graphs using the Vite 6 Environment API. Prevents runtime pollution, invalid cross-environment imports (such as Node.js built-ins leaking into edge or browser bundles), and shared mutable plugin state across compilation environments during multi-environment SSR builds.
globs: vite.config.{ts,js,mjs}, plugins/**/*.ts, src/**/*.{ts,tsx,js,jsx}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite6-environment-api-runtime-isolation-vite-6-environme-469"
---

# Vite 6 Environment API Cross-Runtime Module Isolation Barrier

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Cross-Runtime Module Graph Contamination via Legacy SSR Flags and Shared Plugin State

## System Constraints
You are a Principal Software Architect enforcing the Vite 6 Environment API Cross-Runtime Module Isolation Barrier. Modern SSR frameworks process heterogeneous target runtimes (e.g., client/DOM, workerd/Edge, and Node.js SSR) within the same dev and build lifecycle. You must mandate strict isolation across these environment module graphs, eradicate all reliance on deprecated boolean `ssr` flags in Vite plugins, prevent cross-runtime module resolution contamination, and forbid shared mutable plugin memory across environments.

## Strict Guidelines
- Engineers MUST ALWAYS use `this.environment.name` in Vite plugin hooks (`resolveId`, `load`, `transform`) rather than relying on the deprecated `options?.ssr` boolean flag.
- Engineers MUST explicitly configure discrete environments (`client`, `ssr`, `edge`, `worker`) with customized `resolve.conditions` and `resolve.externalConditions` to prevent Node.js built-ins from resolving in edge/client environments.
- Plugin implementations MUST NEVER maintain global, module-scoped mutable state (caches, transform maps, ASTs) that is not scoped by `environment.name` or keyed directly to `this.environment`.
- Vite configuration MUST explicitly reject Node.js built-in modules (`node:fs`, `node:path`, `node:crypto`) inside client and edge/workerd environment graphs via runtime-specific externalization rules.
- Code interacting with the module runner MUST use the Vite 6 `createRunnableDevEnvironment` or `EnvironmentRunner` API rather than legacy `viteDevServer.ssrLoadModule`.
- Components and shared modules MUST NOT conditionally check `typeof window` to import runtime-restricted native libraries; dynamic runtime-specific dependencies must use environment module aliasing or conditional package export maps.

## Bad vs Good Implementations
### Cross-Environment Plugin Isolation and Condition Scoping

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: The plugin uses the deprecated boolean `options?.ssr` flag, failing to distinguish between Node.js, Cloudflare Workers (workerd), or Deno SSR environments. It also stores transformation artifacts in a shared module-level `Map`, causing client builds and server builds to cross-contaminate and leak memory between environment compilations.
```typescript
import { Plugin, UserConfig } from 'vite';

// Anti-pattern: Shared mutable plugin state across all environments
const transformedModules = new Map<string, string>();

export function brokenPlugin(): Plugin {
  return {
    name: 'broken-cross-runtime-plugin',
    resolveId(id, importer, options) {
      // Legacy Vite 5 boolean check: ignores multi-environment nuance (e.g. edge vs node vs client)
      if (options?.ssr && id === 'virtual:runtime-target') {
        return '\0virtual:runtime-target-ssr';
      }
      return null;
    },
    transform(code, id) {
      // Memory leak & cross-contamination: client and SSR graphs mutate shared map
      transformedModules.set(id, code);
      return null;
    }
  };
}
```

#### Production Standard (Correct)
> **Standard**: Adheres to Vite 6 Environment API standards: plugin execution identifies target runtimes via `this.environment.name`, internal state is strictly isolated per Environment instance using a `WeakMap`, and Vite configuration explicitly sets disjoint resolution conditions (`browser`, `worker`, `node`) across execution targets.
```typescript
import { Plugin, defineConfig } from 'vite';

// Production invariant: Environment-keyed state isolation
const environmentCaches = new WeakMap<object, Map<string, string>>();

export function safeEnvironmentPlugin(): Plugin {
  return {
    name: 'safe-environment-plugin',
    resolveId(id, importer) {
      // Vite 6: Scoped directly to the executing environment instance
      const envName = this.environment.name;
      
      if (id === 'virtual:runtime-target') {
        if (envName === 'client') {
          return '\0virtual:runtime-target-client';
        }
        if (envName === 'edge') {
          return '\0virtual:runtime-target-edge';
        }
        return '\0virtual:runtime-target-ssr';
      }
      return null;
    },
    transform(code, id) {
      // Isolation: Cache is keyed to the current Environment instance
      let envCache = environmentCaches.get(this.environment);
      if (!envCache) {
        envCache = new Map();
        environmentCaches.set(this.environment, envCache);
      }
      envCache.set(id, code);
      return null;
    }
  };
}

// Vite 6 multi-environment definition with strict boundary isolation
export default defineConfig({
  environments: {
    client: {
      resolve: {
        conditions: ['browser'],
        noExternal: true
      }
    },
    edge: {
      resolve: {
        conditions: ['worker', 'edge-light'],
        external: ['cloudflare:workers']
      }
    },
    ssr: {
      resolve: {
        conditions: ['node'],
        externalConditions: ['node']
      }
    }
  }
});
```
Recommended MCP Servers (mcp-serverlist.com)

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

Vite AST & Graph Inspector
Analyzes Vite compilation graph dependencies and detects illegal cross-runtime imports between client and server module nodes.
Recommended Agent Skills (askills.dev)

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

Vite Environment Graph Audit
Inspects Vite 6 multi-environment configurations and verifies module isolation boundaries across worker, node, and client targets.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Cross-Runtime Module Isolation Barrier

Vite 6 Environment API Cross-Runtime Module Isolation Barrier defines an industrial-grade behavioral standard for frontend engineering. Enforces strict physical isolation between client, server, and worker module graphs using the Vite 6 Environment API. Prevents runtime pollution, invalid cross-environment imports (such as Node.js built-ins leaking into edge or browser bundles), and shared mutable plugin state across compilation environments during multi-environment SSR builds. 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 Module Graph Contamination via Legacy SSR Flags and Shared Plugin State 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 Module Graph Contamination via Legacy SSR Flags and Shared Plugin StateCritical
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 use `this.environment.name` in Vite plugin hooks (`resolveId`, `load`, `transform`) rather than relying on the deprecated `options?.ssr` boolean flag.

Engineers MUST ALWAYS use `this.environment.name` in Vite plugin hooks (`resolveId`, `load`, `transform`) rather than relying on the deprecated `options?.ssr` boolean flag.

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 explicitly configure discrete environments (`client`, `ssr`, `edge`, `worker`) with customized `resolve.conditions` and `resolve.externalConditions` to prevent Node.js built-ins from resolving in edge/client environments.

Engineers MUST explicitly configure discrete environments (`client`, `ssr`, `edge`, `worker`) with customized `resolve.conditions` and `resolve.externalConditions` to prevent Node.js built-ins from resolving in edge/client environments.

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 implementations MUST NEVER maintain global, module-scoped mutable state (caches, transform maps, ASTs) that is not scoped by `environment.name` or keyed directly to `this.environment`.

Plugin implementations MUST NEVER maintain global, module-scoped mutable state (caches, transform maps, ASTs) that is not scoped by `environment.name` or keyed directly to `this.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.
4

Vite configuration MUST explicitly reject Node.js built-in modules (`node

Vite configuration MUST explicitly reject Node.js built-in modules (`node:fs`, `node:path`, `node:crypto`) inside client and edge/workerd environment graphs via runtime-specific externalization rules.

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

Code interacting with the module runner MUST use the Vite 6 `createRunnableDevEnvironment` or `EnvironmentRunner` API rather than legacy `viteDevServer.ssrLoadModule`.

Code interacting with the module runner MUST use the Vite 6 `createRunnableDevEnvironment` or `EnvironmentRunner` API rather than legacy `viteDevServer.ssrLoadModule`.

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 shared modules MUST NOT conditionally check `typeof window` to import runtime-restricted native libraries

Components and shared modules MUST NOT conditionally check `typeof window` to import runtime-restricted native libraries; dynamic runtime-specific dependencies must use environment module aliasing or conditional package export maps.

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 Module Isolation Barrier critical for AI coding assistants?

Enforces strict physical isolation between client, server, and worker module graphs using the Vite 6 Environment API. Prevents runtime pollution, invalid cross-environment imports (such as Node.js built-ins leaking into edge or browser bundles), and shared mutable plugin state across compilation environments during multi-environment SSR builds. 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 Module Graph Contamination via Legacy SSR Flags and Shared Plugin State) 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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