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frontendcritical PriorityID: vite-6-environment-api-multi-runtime-isolation-vite-6-environme-755

Vite 6 Environment API Multi-Runtime SSR Isolation Protocol

Enforces strict isolated execution boundaries and per-runtime ModuleRunner instances when leveraging the Vite 6 Environment API across heterogeneous targets (e.g., Client, Node.js SSR, and Cloudflare Workers). Eliminates cross-environment state leaks, shared module graph contamination, and illegal global namespace access between isolated worker runtimes and host processes.

Prohibited Anti-Pattern: Global Module Graph Bleed and Shared ModuleRunner Execution Across Heterogeneous Runtimes

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---
description: Vite 6 Environment API Multi-Runtime SSR Isolation Protocol - Enforces strict isolated execution boundaries and per-runtime ModuleRunner instances when leveraging the Vite 6 Environment API across heterogeneous targets (e.g., Client, Node.js SSR, and Cloudflare Workers). Eliminates cross-environment state leaks, shared module graph contamination, and illegal global namespace access between isolated worker runtimes and host processes.
globs: vite.config.{ts,js,mjs}, src/entry-*.{ts,tsx,js}, src/server/**/*.{ts,js}, src/workers/**/*.{ts,js}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite-6-environment-api-multi-runtime-isolation-vite-6-environme-755"
---

# Vite 6 Environment API Multi-Runtime SSR Isolation Protocol

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Global Module Graph Bleed and Shared ModuleRunner Execution Across Heterogeneous Runtimes

## System Constraints
You are a Principal Software Architect enforcing Vite 6 Environment API Multi-Runtime SSR Isolation. Mandate strict boundaries between client, edge, and node execution contexts. Prevent shared ModuleRunner instances, shared module graphs, and illegal runtime global access.

## Strict Guidelines
- Engineers MUST ALWAYS configure explicit named environments (`client`, `ssr`, `workerd`, etc.) under `environments` in `vite.config.ts` rather than relying on legacy SSR booleans.
- Engineers MUST instantiate separate, dedicated `ModuleRunner` or `createRunnableDevEnvironment` consumers for each runtime environment target to prevent module cache pollution.
- Engineers MUST NOT reference Node-specific globals (`process.env`, `fs`, `path`) inside non-Node runtime environments such as edge workers or browser modules without conditional compile-time isolation.
- Code executing in edge environments MUST resolve dependencies using `resolve.conditions` configured explicitly for that target environment (e.g., `['worker', 'workerd']`).
- Services MUST communicate across Vite 6 environments exclusively via structured `hot.send` or decoupled communication channels, NEVER by passing mutable in-memory module graph nodes.

## Bad vs Good Implementations
### Configuring Heterogeneous Runtimes in Vite 6 Environment API

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Legacy 'ssr' boolean flags configure a single catch-all server target. This causes module resolution conditions to bleed between Node SSR and Cloudflare Workers, leading to runtime crashes when Node APIs are pulled into worker entrypoints.
```typescript
import { defineConfig } from 'vite';

// ANTI-PATTERN: Vite 5 legacy SSR configuration causing shared module resolution
// and leaking Node globals into Worker/Edge targets
export default defineConfig({
  ssr: {
    noExternal: true,
    target: 'webworker',
  },
  build: {
    ssr: true,
  },
});
```

#### Production Standard (Correct)
> **Standard**: Declaring distinct environments guarantees separate module graphs, distinct import resolution conditions, and strictly isolated artifact outputs for Node SSR and Edge Worker targets.
```typescript
import { defineConfig } from 'vite';

// PRODUCTION INVARIANT: Vite 6 Environment API with explicit target isolation
export default defineConfig({
  environments: {
    client: {
      build: { outDir: 'dist/client' },
    },
    ssr: {
      build: { outDir: 'dist/ssr' },
      resolve: {
        conditions: ['node'],
        externalConditions: ['node'],
      },
    },
    edge: {
      build: { outDir: 'dist/edge' },
      resolve: {
        noExternal: true,
        conditions: ['worker', 'workerd', 'browser'],
      },
    },
  },
});
```

### Instantiating Isolated ModuleRunner per Environment in Dev Server

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: server.ssrLoadModule uses the default Node runtime context and module cache for both entry points, poisoning the edge entry with Node modules and violating runtime execution assumptions.
```typescript
import { createServer } from 'vite';

// ANTI-PATTERN: Using global ssrLoadModule across mixed edge and node code
const server = await createServer();
const nodeHandler = await server.ssrLoadModule('/src/entry-node.ts');
const edgeHandler = await server.ssrLoadModule('/src/entry-edge.ts');
```

#### Production Standard (Correct)
> **Standard**: Utilizes Vite 6's server.environments API with dedicated ModuleRunner instances, guaranteeing that module evaluation, caches, and dependency trees remain hermetically sealed per runtime.
```typescript
import { createServer } from 'vite';
import { ModuleRunner, ESModulesEvaluator } from 'vite/module-runner';

// PRODUCTION INVARIANT: Query the isolated DevEnvironment and attach dedicated ModuleRunners
const server = await createServer();

const ssrEnvironment = server.environments.ssr;
const edgeEnvironment = server.environments.edge;

// Dedicated runner for Node environment
const ssrRunner = new ModuleRunner(
  ssrEnvironment,
  new ESModulesEvaluator()
);
const nodeModule = await ssrRunner.import('/src/entry-node.ts');

// Dedicated runner for Edge environment using isolated transport
const edgeRunner = new ModuleRunner(
  edgeEnvironment,
  new ESModulesEvaluator()
);
const edgeModule = await edgeRunner.import('/src/entry-edge.ts');
```
Recommended MCP Servers (mcp-serverlist.com)

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

Vite DevTools Inspection MCP
Exposes live Vite server module graphs and environment states to verify boundary isolation.
Recommended Agent Skills (askills.dev)

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

Vite Environment Verifier
CLI tool that statically audits vite.config.ts environments and prevents illegal cross-runtime imports.
Architectural Specification & Invariant Rationale

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

Vite 6 Environment API Multi-Runtime SSR Isolation Protocol defines an industrial-grade behavioral standard for frontend engineering. Enforces strict isolated execution boundaries and per-runtime ModuleRunner instances when leveraging the Vite 6 Environment API across heterogeneous targets (e.g., Client, Node.js SSR, and Cloudflare Workers). Eliminates cross-environment state leaks, shared module graph contamination, and illegal global namespace access between isolated worker runtimes and host processes. 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 Module Graph Bleed and Shared ModuleRunner Execution Across Heterogeneous 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 Module Graph Bleed and Shared ModuleRunner Execution Across Heterogeneous 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 named environments (`client`, `ssr`, `workerd`, etc.) under `environments` in `vite.config.ts` rather than relying on legacy SSR booleans.

Engineers MUST ALWAYS configure explicit named environments (`client`, `ssr`, `workerd`, etc.) under `environments` in `vite.config.ts` rather than relying on legacy SSR booleans.

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 instantiate separate, dedicated `ModuleRunner` or `createRunnableDevEnvironment` consumers for each runtime environment target to prevent module cache pollution.

Engineers MUST instantiate separate, dedicated `ModuleRunner` or `createRunnableDevEnvironment` consumers for each runtime environment target to prevent module cache pollution.

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 NOT reference Node-specific globals (`process.env`, `fs`, `path`) inside non-Node runtime environments such as edge workers or browser modules without conditional compile-time isolation.

Engineers MUST NOT reference Node-specific globals (`process.env`, `fs`, `path`) inside non-Node runtime environments such as edge workers or browser modules without conditional compile-time isolation.

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 executing in edge environments MUST resolve dependencies using `resolve.conditions` configured explicitly for that target environment (e.g., `['worker', 'workerd']`).

Code executing in edge environments MUST resolve dependencies using `resolve.conditions` configured explicitly for that target environment (e.g., `['worker', '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.
5

Services MUST communicate across Vite 6 environments exclusively via structured `hot.send` or decoupled communication channels, NEVER by passing mutable in-memory module graph nodes.

Services MUST communicate across Vite 6 environments exclusively via structured `hot.send` or decoupled communication channels, NEVER by passing mutable in-memory module graph nodes.

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 Isolation Protocol critical for AI coding assistants?

Enforces strict isolated execution boundaries and per-runtime ModuleRunner instances when leveraging the Vite 6 Environment API across heterogeneous targets (e.g., Client, Node.js SSR, and Cloudflare Workers). Eliminates cross-environment state leaks, shared module graph contamination, and illegal global namespace access between isolated worker runtimes and host processes. 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 Module Graph Bleed and Shared ModuleRunner Execution Across Heterogeneous 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.

Open Specification · CC BY 4.0·Free for Personal, Team & Commercial In-Repo Use

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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