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frontendcritical PriorityID: vite6-environment-api-runtime-isolation-vite-6-environme-876

Vite 6 Environment API Multi-Runtime State & Module Boundary Isolation

Enforces strict module execution boundaries, module graph separation, and memory isolation between heterogeneous runtime targets (e.g., workerd/Cloudflare Workers, Node.js SSR runners, and Client DOM) using the Vite 6 Environment API. Prevents cross-environment reference leakage, dual-package hazard instantiation, and state pollution during unified SSR and dev orchestration.

Prohibited Anti-Pattern: Cross-Environment State Leaks and Shared Module Graph Contamination in Unified SSR

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---
description: Vite 6 Environment API Multi-Runtime State & Module Boundary Isolation - Enforces strict module execution boundaries, module graph separation, and memory isolation between heterogeneous runtime targets (e.g., workerd/Cloudflare Workers, Node.js SSR runners, and Client DOM) using the Vite 6 Environment API. Prevents cross-environment reference leakage, dual-package hazard instantiation, and state pollution during unified SSR and dev orchestration.
globs: vite.config.{ts,js,mjs}, src/entry.*.{ts,tsx,js,jsx}, src/server/**/*.{ts,tsx}, src/client/**/*.{ts,tsx}, src/workers/**/*.{ts,tsx}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite6-environment-api-runtime-isolation-vite-6-environme-876"
---

# Vite 6 Environment API Multi-Runtime State & Module Boundary Isolation

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Cross-Environment State Leaks and Shared Module Graph Contamination in Unified SSR

## System Constraints
You are a Principal Architect enforcing strict multi-runtime state isolation via the Vite 6 Environment API. Mandate zero cross-contamination across client, node, and edge runtimes (such as Cloudflare workerd). Ensure that plugins, transform pipelines, module runners, and hot module replacement (HMR) handlers explicitly target the correct Vite Environment context. Reject legacy `ssrContext` hacks, global state assumptions, and unauthorized shared module graph evaluations.

## Strict Guidelines
- Engineers MUST ALWAYS configure distinct runtime environments under `environments` in Vite 6 (e.g., `client`, `ssr`, `workerd`) with explicit `resolve.conditions` and `consumer` definitions.
- Engineers MUST NOT access global Node.js primitives (`process`, `Buffer`, `__dirname`) in universal modules intended for execution within isolated edge runtimes like `workerd`.
- Plugins MUST utilize `this.environment` within lifecycle hooks (`transform`, `resolveId`, `load`) to selectively execute environment-specific logic rather than inspecting legacy `options.ssr` flags.
- Code MUST rely on `ModuleRunner` instances scoped directly to the target environment (`server.environments[name].runner.import()`) rather than deprecated `server.ssrLoadModule()`.
- Services MUST NOT share in-memory singleton caches, module instances, or state stores across runtime environment execution boundaries.
- Components NEVER import edge-only or Node-only drivers directly into shared tree modules without dedicated environment conditional exports or dynamic runner boundaries.

## Bad vs Good Implementations
### Legacy SSR Execution vs. Vite 6 Scoped Environment ModuleRunner

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Using deprecated `vite.ssrLoadModule` bypasses Vite 6's Environment API, forcing edge (workerd) or custom runtime code into the host Node.js runtime process, leading to global pollution, missing runtime polyfills, and invalid module graph resolution.
```typescript
import { createServer } from 'vite';

const vite = await createServer({
  server: { middlewareMode: true },
  appType: 'custom',
});

// ANTI-PATTERN: Deprecated Vite 5 style ssrLoadModule ignores runtime boundaries,
// executing edge code inside the Node.js Vite process and sharing node_modules memory.
export async function handleRequest(url: string) {
  const { render } = await vite.ssrLoadModule('/src/entry.server.ts');
  return render(url);
}
```

#### Production Standard (Correct)
> **Standard**: Defines discrete environments with specific resolution conditions and utilizes the isolated `environment.runner.import` method, maintaining rigorous module graph boundaries between Node and Edge targets.
```typescript
import { createServer } from 'vite';

const vite = await createServer({
  server: { middlewareMode: true },
  appType: 'custom',
  environments: {
    client: {},
    ssr: {
      resolve: {
        conditions: ['node', 'import'],
      },
    },
    workerd: {
      resolve: {
        conditions: ['workerd', 'worker', 'import'],
        noExternal: true,
      },
    },
  },
});

// PRODUCTION FIX: Explicitly target the scoped environment runner.
// Keeps the module graph and evaluation memory isolated to the target execution profile.
export async function handleRequest(url: string, targetEnv: 'ssr' | 'workerd') {
  const environment = vite.environments[targetEnv];
  if (!environment || !environment.runner) {
    throw new Error(`Environment ${targetEnv} is not properly configured with a runner.`);
  }
  const { render } = await environment.runner.import('/src/entry.server.ts');
  return render(url);
}
```

### Plugin Migration from `options.ssr` to `this.environment` API

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: The legacy `options?.ssr` flag only bifurcates into client and generic SSR, breaking runtime-specific transformations when multiple environments (e.g., edge worker vs. node) coexist.
```typescript
import type { Plugin } from 'vite';

export function brokenRuntimePlugin(): Plugin {
  return {
    name: 'broken-runtime-plugin',
    transform(code, id, options) {
      // ANTI-PATTERN: options?.ssr is a binary flag that fails in multi-environment architectures
      // where 'ssr' might mean Node.js, workerd, or an embedded quickjs instance.
      if (options?.ssr) {
        return code.replace('__RUNTIME_TARGET__', JSON.stringify('server'));
      }
      return code.replace('__RUNTIME_TARGET__', JSON.stringify('client'));
    },
  };
}
```

#### Production Standard (Correct)
> **Standard**: Leverages `this.environment.name` in plugin hooks to enforce distinct transformation logic per declared execution target, preventing unintended cross-target code substitutions.
```typescript
import type { Plugin } from 'vite';

export function isolatedRuntimePlugin(): Plugin {
  return {
    name: 'isolated-runtime-plugin',
    // PRODUCTION FIX: Access context-aware environment state directly from plugin hook context
    transform(code, id) {
      const envName = this.environment.name;

      if (envName === 'workerd') {
        return code.replace('__RUNTIME_TARGET__', JSON.stringify('cloudflare-workerd'));
      }
      if (envName === 'ssr') {
        return code.replace('__RUNTIME_TARGET__', JSON.stringify('node-ssr'));
      }
      return code.replace('__RUNTIME_TARGET__', JSON.stringify('client-dom'));
    },
  };
}
```
Recommended MCP Servers (mcp-serverlist.com)

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

Fetch MCP Server
Validates dynamic external imports and HTTP endpoints against edge runtime compatibility schemas.
Recommended Agent Skills (askills.dev)

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

Vite Environment Inspector CLI
CLI skill that audits vite.config.ts to detect legacy ssr options and verify Vite 6 environment declarations.
Architectural Specification & Invariant Rationale

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

Vite 6 Environment API Multi-Runtime State & Module Boundary Isolation defines an industrial-grade behavioral standard for frontend engineering. Enforces strict module execution boundaries, module graph separation, and memory isolation between heterogeneous runtime targets (e.g., workerd/Cloudflare Workers, Node.js SSR runners, and Client DOM) using the Vite 6 Environment API. Prevents cross-environment reference leakage, dual-package hazard instantiation, and state pollution during unified SSR and dev orchestration. 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 State Leaks and Shared Module Graph Contamination in Unified 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-Environment State Leaks and Shared Module Graph Contamination in Unified 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 distinct runtime environments under `environments` in Vite 6 (e.g., `client`, `ssr`, `workerd`) with explicit `resolve.conditions` and `consumer` definitions.

Engineers MUST ALWAYS configure distinct runtime environments under `environments` in Vite 6 (e.g., `client`, `ssr`, `workerd`) with explicit `resolve.conditions` and `consumer` definitions.

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 global Node.js primitives (`process`, `Buffer`, `__dirname`) in universal modules intended for execution within isolated edge runtimes like `workerd`.

Engineers MUST NOT access global Node.js primitives (`process`, `Buffer`, `__dirname`) in universal modules intended for execution within isolated edge runtimes like `workerd`.

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 MUST utilize `this.environment` within lifecycle hooks (`transform`, `resolveId`, `load`) to selectively execute environment-specific logic rather than inspecting legacy `options.ssr` flags.

Plugins MUST utilize `this.environment` within lifecycle hooks (`transform`, `resolveId`, `load`) to selectively execute environment-specific logic rather than inspecting legacy `options.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.
4

Code MUST rely on `ModuleRunner` instances scoped directly to the target environment (`server.environments[name].runner.import()`) rather than deprecated `server.ssrLoadModule()`.

Code MUST rely on `ModuleRunner` instances scoped directly to the target environment (`server.environments[name].runner.import()`) rather than deprecated `server.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.
5

Services MUST NOT share in-memory singleton caches, module instances, or state stores across runtime environment execution boundaries.

Services MUST NOT share in-memory singleton caches, module instances, or state stores across runtime environment execution boundaries.

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 NEVER import edge-only or Node-only drivers directly into shared tree modules without dedicated environment conditional exports or dynamic runner boundaries.

Components NEVER import edge-only or Node-only drivers directly into shared tree modules without dedicated environment conditional exports or dynamic runner boundaries.

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 State & Module Boundary Isolation critical for AI coding assistants?

Enforces strict module execution boundaries, module graph separation, and memory isolation between heterogeneous runtime targets (e.g., workerd/Cloudflare Workers, Node.js SSR runners, and Client DOM) using the Vite 6 Environment API. Prevents cross-environment reference leakage, dual-package hazard instantiation, and state pollution during unified SSR and dev orchestration. 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 State Leaks and Shared Module Graph Contamination in Unified 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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