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frontendcritical PriorityID: vite-6-environment-api-multi-runtime-isolation-vite-6-environme-493

Vite 6 Multi-Runtime Environment API Module Graph Isolation Standard

Enforces strict module graph isolation across distinct execution targets (client, ssr, workerd/edge) using Vite 6's Environment API. Prevents cross-runtime symbol contamination, invalid module caching across disparate compilation contexts, and broken HMR state synchronizations during concurrent SSR and client dev cycles.

Prohibited Anti-Pattern: Monolithic Module Graph Leaks and Deprecated ssrLoadModule Traversal in Heterogeneous Runtimes

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---
description: Vite 6 Multi-Runtime Environment API Module Graph Isolation Standard - Enforces strict module graph isolation across distinct execution targets (client, ssr, workerd/edge) using Vite 6's Environment API. Prevents cross-runtime symbol contamination, invalid module caching across disparate compilation contexts, and broken HMR state synchronizations during concurrent SSR and client dev cycles.
globs: vite.config.{ts,js,mjs}, server/**/*.{ts,js}, src/**/*.{ts,tsx,js,jsx}
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-493"
---

# Vite 6 Multi-Runtime Environment API Module Graph Isolation Standard

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Monolithic Module Graph Leaks and Deprecated ssrLoadModule Traversal in Heterogeneous Runtimes

## System Constraints
You are a Principal Software Architect enforcing the Vite 6 Environment API Multi-Runtime Module Isolation Standard. You must mandate strict physical and logical boundaries between module graphs for different runtime targets (e.g., browser client, Node.js SSR, Cloudflare workerd). Forbid legacy Vite 4/5 monolithic APIs like root `server.moduleGraph` or `server.ssrLoadModule` in multi-runtime contexts, ensuring that plugins and dev-server middlewares scope all transforms, resolution checks, and HMR events to `this.environment` or `server.environments[name]`.

## Strict Guidelines
- Engineers MUST ALWAYS configure distinct runtime definitions inside the `environments` config block (e.g., `environments.client`, `environments.ssr`, `environments.edge`) rather than relying on global `ssr` flags.
- Engineers MUST NOT access `server.moduleGraph` or call `server.ssrLoadModule` directly in Vite 6 multi-runtime setups; code must resolve modules via `server.environments[name].moduleGraph` or `server.environments[name].runner.import`.
- Custom Vite plugins MUST implement `applyToEnvironment(environment)` or check `this.environment.name` to prevent node-only/edge-only transforms from polluting alternate runtime module graphs.
- Services handling HMR invalidation MUST emit hot-updates via the target environment's channel (`environment.hot.send`) rather than broadcasting globally through `server.ws.send`.
- Components and server modules NEVER import runtime-specific host globals or native modules (`node:fs`, `node:async_hooks`, `cloudflare:workers`) without runtime target gating and environment-specific externalization.

## Bad vs Good Implementations
### Configuring Multi-Runtime Isolation and Scoped Plugin Transforms in Vite 6

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Using top-level `ssr` config and `options?.ssr` treats all server contexts identically. When targeting multiple non-browser runtimes (e.g., Cloudflare workerd alongside Node.js background workers), this produces cache collisions, leaks Node APIs into edge runtimes, and bypasses Vite 6's per-environment ModuleGraph.
```typescript
import { defineConfig, type ViteDevServer, type Plugin } from 'vite';

// ANTI-PATTERN: Vite 5 monolithic configuration and legacy ssrLoadModule
export default defineConfig({
  ssr: {
    target: 'node',
    noExternal: ['shared-ui']
  },
  plugins: [{
    name: 'runtime-resolver',
    transform(code, id, options) {
      // Leaks Node builtins into edge/client graphs because options?.ssr is a single boolean
      if (options?.ssr) {
        return code.replace('__RUNTIME__', '"node"');
      }
      return code.replace('__RUNTIME__', '"browser"');
    }
  }]
});

export async function handleRequest(server: ViteDevServer, url: string) {
  // Deprecated global loader mixes module caches across runtimes
  const entry = await server.ssrLoadModule(url);
  return entry.default();
}
```

#### Production Standard (Correct)
> **Standard**: Vite 6's Environment API provisions dedicated `DevEnvironment` instances with segregated `moduleGraph` instances and execution runtimes (`runner.import`). Plugins utilize `applyToEnvironment` and `this.environment.name` to eliminate runtime bleed and cross-environment compilation race conditions.
```typescript
import { defineConfig, type ViteDevServer, type Plugin } from 'vite';

// PRODUCTION FIX: Vite 6 Environment API with isolated runtime graphs
export default defineConfig({
  environments: {
    client: {
      build: { outDir: 'dist/client' }
    },
    ssr: {
      build: { outDir: 'dist/ssr' },
      resolve: { conditions: ['node', 'import'] }
    },
    edge: {
      build: { outDir: 'dist/edge' },
      resolve: { conditions: ['workerd', 'worker', 'import'] }
    }
  },
  plugins: [{
    name: 'runtime-resolver',
    applyToEnvironment(environment) {
      // Only apply this plugin logic to server and edge environments
      return environment.name !== 'client';
    },
    transform(code, id) {
      // Scoped strictly to the active compilation environment
      const runtimeName = this.environment.name;
      return {
        code: code.replace('__RUNTIME__', JSON.stringify(runtimeName)),
        map: null
      };
    }
  } as Plugin]
});

export async function handleRequest(server: ViteDevServer, envName: 'ssr' | 'edge', url: string) {
  const targetEnv = server.environments[envName];
  if (!targetEnv || !('runner' in targetEnv)) {
    throw new Error(`Invalid or non-runnable environment: ${envName}`);
  }
  // Invokes isolated ModuleRunner within specific runtime execution sandbox
  const entry = await targetEnv.runner.import(url);
  return entry.default();
}
```
Recommended MCP Servers (mcp-serverlist.com)

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

Vite DevTools MCP
Inspects Vite 6 runtime environments, isolated module graphs, and active HMR invalidation channels.
Recommended Agent Skills (askills.dev)

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

Vite Environment Graph Inspector
CLI skill to query and validate environment-specific module graphs and assert isolation during SSR/client builds.
Architectural Specification & Invariant Rationale

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

Vite 6 Multi-Runtime Environment API Module Graph Isolation Standard defines an industrial-grade behavioral standard for frontend engineering. Enforces strict module graph isolation across distinct execution targets (client, ssr, workerd/edge) using Vite 6's Environment API. Prevents cross-runtime symbol contamination, invalid module caching across disparate compilation contexts, and broken HMR state synchronizations during concurrent SSR and client dev cycles. 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: Monolithic Module Graph Leaks and Deprecated ssrLoadModule Traversal in 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 DriftMonolithic Module Graph Leaks and Deprecated ssrLoadModule Traversal in 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 distinct runtime definitions inside the `environments` config block (e.g., `environments.client`, `environments.ssr`, `environments.edge`) rather than relying on global `ssr` flags.

Engineers MUST ALWAYS configure distinct runtime definitions inside the `environments` config block (e.g., `environments.client`, `environments.ssr`, `environments.edge`) rather than relying on global `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 NOT access `server.moduleGraph` or call `server.ssrLoadModule` directly in Vite 6 multi-runtime setups

Engineers MUST NOT access `server.moduleGraph` or call `server.ssrLoadModule` directly in Vite 6 multi-runtime setups; code must resolve modules via `server.environments[name].moduleGraph` or `server.environments[name].runner.import`.

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

Custom Vite plugins MUST implement `applyToEnvironment(environment)` or check `this.environment.name` to prevent node-only/edge-only transforms from polluting alternate runtime module graphs.

Custom Vite plugins MUST implement `applyToEnvironment(environment)` or check `this.environment.name` to prevent node-only/edge-only transforms from polluting alternate runtime 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.
4

Services handling HMR invalidation MUST emit hot-updates via the target environment's channel (`environment.hot.send`) rather than broadcasting globally through `server.ws.send`.

Services handling HMR invalidation MUST emit hot-updates via the target environment's channel (`environment.hot.send`) rather than broadcasting globally through `server.ws.send`.

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

Components and server modules NEVER import runtime-specific host globals or native modules (`node

Components and server modules NEVER import runtime-specific host globals or native modules (`node:fs`, `node:async_hooks`, `cloudflare:workers`) without runtime target gating and environment-specific externalization.

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 Multi-Runtime Environment API Module Graph Isolation Standard critical for AI coding assistants?

Enforces strict module graph isolation across distinct execution targets (client, ssr, workerd/edge) using Vite 6's Environment API. Prevents cross-runtime symbol contamination, invalid module caching across disparate compilation contexts, and broken HMR state synchronizations during concurrent SSR and client dev cycles. 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 (Monolithic Module Graph Leaks and Deprecated ssrLoadModule Traversal in 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.

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Citation & Open Source Attribution Guidelines

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