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frontendcritical PriorityID: vite6-environment-api-runtime-isolation-vite-6-environme-640

Vite 6 Environment API Multi-Runtime SSR Execution Isolation

Enforces strict process, module graph, and memory isolation between distinct execution environments (Workerd/Cloudflare, Node.js, WebAssembly, and Client) when using Vite 6 Environment API. Prevents shared mutable state leakage, incorrect runtime primitive contamination, and invalid module runner resolution across heterogeneous dev and SSR graphs.

Prohibited Anti-Pattern: Global Scope Pollution and Shared Module Graph Bleed Across Heterogeneous Vite 6 SSR Runtimes

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---
description: Vite 6 Environment API Multi-Runtime SSR Execution Isolation - Enforces strict process, module graph, and memory isolation between distinct execution environments (Workerd/Cloudflare, Node.js, WebAssembly, and Client) when using Vite 6 Environment API. Prevents shared mutable state leakage, incorrect runtime primitive contamination, and invalid module runner resolution across heterogeneous dev and SSR graphs.
globs: vite.config.{ts,js,mjs}, src/entry-*.{ts,js}, src/server/**/*.{ts,js}, src/runtimes/**/*.{ts,js}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite6-environment-api-runtime-isolation-vite-6-environme-640"
---

# Vite 6 Environment API Multi-Runtime SSR Execution Isolation

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Global Scope Pollution and Shared Module Graph Bleed Across Heterogeneous Vite 6 SSR Runtimes

## System Constraints
You are a Principal Software Architect enforcing Vite 6 Environment API Multi-Runtime SSR Execution Isolation. You must ensure that applications targeting multi-runtime configurations (e.g., Node.js orchestration alongside Cloudflare Workerd edge runners and WebAssembly sandboxes) maintain absolute module graph boundaries. Disallow reliance on process.env or globalThis for stateful runtime singletons, enforce separate DevEnvironment instances, mandate explicit ModuleRunner instantiation with environment-specific transport/evaluator channels, and prohibit leaky dual-runtime imports across distinct compilation and execution graphs.

## Strict Guidelines
- Engineers MUST ALWAYS configure explicit, isolated `environments` keys in `vite.config.ts` (e.g., `environments.ssr` for Node.js, `environments.edge` for Workerd) instead of relying on legacy `ssr` root configuration flags.
- Engineers MUST NEVER access runtime-specific host globals (`process.versions.node`, `Buffer`, `navigator.userAgent`, Cloudflare Worker bindings) inside universal code without dynamic branching guarded by environment-specific entrypoints.
- Engineers MUST instantiate separate `ModuleRunner` instances for each runtime boundary using distinct `ModuleEvaluator` implementations (e.g., `ESModulesEvaluator` for Node.js, isolated evaluation shims for Workerd) to avoid caching cross-target ASTs.
- Vite plugins with runtime transforms MUST check `this.environment.name` instead of `options.ssr` inside plugin hooks (`transform`, `resolveId`, `load`) to ensure environment-specific transform pipelines.
- Engineers MUST NOT leak stateful singletons or module-scoped caches across execution contexts; all execution payloads across the Node.js dev server and non-Node.js runners MUST be passed via structured serialization over defined transport bridges.

## Bad vs Good Implementations
### Configuring Vite 6 Isolated DevEnvironments with Target-Specific Runtimes

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Using legacy `ssr` flags forces all SSR targets through a single module graph and transform pipeline. This leaks Node.js dependencies and compilation behaviors into edge/Workerd runtimes and causes module cache collision.
```typescript
import { defineConfig } from 'vite';

// ANTI-PATTERN: Vite 5 legacy config mixing Node SSR and Edge contexts.
// Transforms run under a single SSR module graph, leaking Node globals into Worker targets.
export default defineConfig({
  ssr: {
    target: 'node',
    noExternal: true,
  },
  plugins: [{
    name: 'runtime-patch',
    transform(code, id, options) {
      // Flawed binary ssr flag assumption
      if (options?.ssr) {
        return code.replace('__RUNTIME__', JSON.stringify(process.env.NODE_ENV));
      }
      return code;
    },
  }],
});
```

#### Production Standard (Correct)
> **Standard**: Defines discrete execution environments with target-specific resolution conditions, output paths, and context-aware transformations bound to `this.environment.name`.
```typescript
import { defineConfig } from 'vite';
import { createWorkerdHandler } from 'my-vite-workerd-plugin';

export default defineConfig({
  environments: {
    client: {
      build: { outDir: 'dist/client' },
    },
    ssr: {
      build: { outDir: 'dist/ssr' },
      resolve: { ssrConditions: ['node', 'import'] },
    },
    edge: {
      build: { outDir: 'dist/edge' },
      resolve: { ssrConditions: ['worker', 'workerd', 'browser'] },
    },
  },
  plugins: [{
    name: 'runtime-patch',
    transform(code, id) {
      // Vite 6 Environment API invariant: scope transforms strictly by environment name
      if (this.environment.name === 'edge') {
        return code.replace('__RUNTIME__', JSON.stringify('workerd'));
      }
      if (this.environment.name === 'ssr') {
        return code.replace('__RUNTIME__', JSON.stringify('node'));
      }
      return code;
    },
  }],
});
```

### Executing Isolated SSR via Vite 6 ModuleRunner Transport

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Using `server.ssrLoadModule` runs untrusted target code directly in the Node.js server thread, circumventing memory isolation and causing edge runtime mock corruption.
```typescript
import { createServer } from 'vite';

const server = await createServer();

// ANTI-PATTERN: Using deprecated ssrLoadModule across multiple runtime targets
// Evaluates code in current host process, polluting Node host memory with edge state
export async function handleRequest(url: string, targetRuntime: 'node' | 'edge') {
  const entry = await server.ssrLoadModule('/src/entry.ts');
  return entry.render(url);
}
```

#### Production Standard (Correct)
> **Standard**: Instantiates dedicated ModuleRunners and delegates edge executions through configured dev environment transport protocols rather than evaluating in host memory.
```typescript
import { createServer } from 'vite';
import { createNodeModuleRunner } from 'vite/module-runner';

const server = await createServer();

// Vite 6 Invariant: Isolate ModuleRunner execution using environment-specific instances
const nodeEnvironment = server.environments.ssr;
const edgeEnvironment = server.environments.edge;

const nodeRunner = createNodeModuleRunner(nodeEnvironment);

export async function handleRequest(url: string, targetRuntime: 'node' | 'edge') {
  if (targetRuntime === 'node') {
    const entry = await nodeRunner.import('/src/entry-node.ts');
    return entry.render(url);
  }

  // Workerd execution routed via dedicated environment runner over isolated transport channel
  const edgeRunnerTransport = edgeEnvironment.hot;
  return edgeRunnerTransport.send('execute-render', { url });
}
```
Recommended MCP Servers (mcp-serverlist.com)

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

Vite Module Graph Analyzer MCP
Inspects Vite 6 Environment API module graphs to verify zero cross-contamination of isolated nodes between ssr, edge, and client environments.
Recommended Agent Skills (askills.dev)

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

Vite Environment Doctor CLI
CLI diagnostic utility to detect cross-environment module leaks and legacy SSR API usages in Vite 6 projects.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Multi-Runtime SSR Execution Isolation

Vite 6 Environment API Multi-Runtime SSR Execution Isolation defines an industrial-grade behavioral standard for frontend engineering. Enforces strict process, module graph, and memory isolation between distinct execution environments (Workerd/Cloudflare, Node.js, WebAssembly, and Client) when using Vite 6 Environment API. Prevents shared mutable state leakage, incorrect runtime primitive contamination, and invalid module runner resolution across heterogeneous dev and SSR graphs. 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: Global Scope Pollution and Shared Module Graph Bleed Across Heterogeneous Vite 6 SSR Runtimes 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 DriftGlobal Scope Pollution and Shared Module Graph Bleed Across Heterogeneous Vite 6 SSR RuntimesCritical
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 explicit, isolated `environments` keys in `vite.config.ts` (e.g., `environments.ssr` for Node.js, `environments.edge` for Workerd) instead of relying on legacy `ssr` root configuration flags.

Engineers MUST ALWAYS configure explicit, isolated `environments` keys in `vite.config.ts` (e.g., `environments.ssr` for Node.js, `environments.edge` for Workerd) instead of relying on legacy `ssr` root configuration 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 NEVER access runtime-specific host globals (`process.versions.node`, `Buffer`, `navigator.userAgent`, Cloudflare Worker bindings) inside universal code without dynamic branching guarded by environment-specific entrypoints.

Engineers MUST NEVER access runtime-specific host globals (`process.versions.node`, `Buffer`, `navigator.userAgent`, Cloudflare Worker bindings) inside universal code without dynamic branching guarded by environment-specific entrypoints.

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 instantiate separate `ModuleRunner` instances for each runtime boundary using distinct `ModuleEvaluator` implementations (e.g., `ESModulesEvaluator` for Node.js, isolated evaluation shims for Workerd) to avoid caching cross-target ASTs.

Engineers MUST instantiate separate `ModuleRunner` instances for each runtime boundary using distinct `ModuleEvaluator` implementations (e.g., `ESModulesEvaluator` for Node.js, isolated evaluation shims for Workerd) to avoid caching cross-target ASTs.

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 plugins with runtime transforms MUST check `this.environment.name` instead of `options.ssr` inside plugin hooks (`transform`, `resolveId`, `load`) to ensure environment-specific transform pipelines.

Vite plugins with runtime transforms MUST check `this.environment.name` instead of `options.ssr` inside plugin hooks (`transform`, `resolveId`, `load`) to ensure environment-specific transform pipelines.

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

Engineers MUST NOT leak stateful singletons or module-scoped caches across execution contexts

Engineers MUST NOT leak stateful singletons or module-scoped caches across execution contexts; all execution payloads across the Node.js dev server and non-Node.js runners MUST be passed via structured serialization over defined transport bridges.

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 SSR Execution Isolation critical for AI coding assistants?

Enforces strict process, module graph, and memory isolation between distinct execution environments (Workerd/Cloudflare, Node.js, WebAssembly, and Client) when using Vite 6 Environment API. Prevents shared mutable state leakage, incorrect runtime primitive contamination, and invalid module runner resolution across heterogeneous dev and SSR graphs. 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 (Global Scope Pollution and Shared Module Graph Bleed Across Heterogeneous Vite 6 SSR Runtimes) 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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