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frontendcritical PriorityID: vite6-environment-api-runtime-isolation-standard-vite-6-environme-199

Vite 6 Environment API Multi-Runtime Context Isolation & Memory Sandboxing

Enforces strict memory, execution context, and global scope isolation when executing heterogeneous SSR pipelines across browser, Node.js, and edge workers via Vite 6 Environment API. Prevents cross-runtime state leakage, globalThis pollution, and invalid shared module cache reuse during concurrent Hot Module Replacement (HMR).

Prohibited Anti-Pattern: Cross-Environment Global Scope Contamination and Shared Module Graph Leaks in Multi-Runtime SSR

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---
description: Vite 6 Environment API Multi-Runtime Context Isolation & Memory Sandboxing - Enforces strict memory, execution context, and global scope isolation when executing heterogeneous SSR pipelines across browser, Node.js, and edge workers via Vite 6 Environment API. Prevents cross-runtime state leakage, globalThis pollution, and invalid shared module cache reuse during concurrent Hot Module Replacement (HMR).
globs: vite.config.{ts,js,mjs}, src/entry.*.{ts,tsx,js,jsx}, src/server/**/*.{ts,tsx}, src/runtimes/**/*.{ts,tsx}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite6-environment-api-runtime-isolation-standard-vite-6-environme-199"
---

# Vite 6 Environment API Multi-Runtime Context Isolation & Memory Sandboxing

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Cross-Environment Global Scope Contamination and Shared Module Graph Leaks in Multi-Runtime SSR

## System Constraints
You are a Principal Software Architect enforcing Vite 6 Environment API isolation invariants. You must prevent global scope contamination, cross-environment module graph leaks, and shared singleton mutations across client, server, and edge worker runtimes during concurrent development and HMR.

## Strict Guidelines
- Engineers MUST ALWAYS instantiate dedicated environments via `createDevEnvironment` or target existing environments via `server.environments[name]` rather than legacy `server.ssrLoadModule`.
- Engineers MUST NOT mutate `globalThis` or process-level globals to share state or provide runtime-specific polyfills across different runtime environments.
- Code MUST isolate execution contexts using Vite 6 `ModuleRunner` with runtime-specific `runnerOptions` (evaluator or VM sandbox) instead of sharing single-context execution.
- Custom environments (such as Cloudflare Workers or Node.js) MUST explicitly define isolated `resolve.conditions` and `resolve.externalConditions` to prevent cross-runtime resolution bleed.
- HMR listeners and event emitters MUST be bound to `environment.hot` rather than root `server.hot` to prevent runtime dispatch collisions.

## Bad vs Good Implementations
### Configuring Multi-Runtime Isolation with Vite 6 Environment API

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Uses legacy `server.ssrLoadModule` which runs all SSR code within the ambient Node.js process without runtime boundary enforcement. Mutates `globalThis` which corrupts isolate isolation and triggers memory leaks across concurrent SSR runs and HMR cycles.
```typescript
import { defineConfig } from 'vite';

export default defineConfig({
  // DEPRECATED & UNSAFE: Legacy SSR setup pooling Node and Edge dependencies together
  ssr: {
    noExternal: ['shared-lib'],
    target: 'node',
  },
  plugins: [{
    name: 'leak-global-context',
    configureServer(server) {
      // Shared global mutation leaks across all SSR requests and HMR reloads
      (globalThis as any).__RUNTIME_CACHE__ = new Map();
      return () => {
        server.middlewares.use(async (req, res, next) => {
          // Concurrently executes Edge code directly in the Node.js root process context
          const mod = await server.ssrLoadModule('/src/entry.edge.ts');
          await mod.render(req, res);
        });
      };
    },
  }],
});
```

#### Production Standard (Correct)
> **Standard**: Defines explicit `environments` ('client', 'ssr', 'edge') with discrete resolution conditions. Uses Vite 6 `createServerModuleRunner` pinned specifically to `edgeEnv` to enforce clean execution sandboxing and isolated HMR handling.
```typescript
import { defineConfig, createServerModuleRunner } from 'vite';

export default defineConfig({
  environments: {
    client: {
      build: { outDir: 'dist/client' },
    },
    ssr: {
      build: { outDir: 'dist/ssr' },
      resolve: {
        conditions: ['node'],
      },
    },
    edge: {
      build: { outDir: 'dist/edge' },
      resolve: {
        noExternal: true,
        conditions: ['worker', 'edge-routine'],
      },
    },
  },
  plugins: [{
    name: 'isolated-runtime-runner',
    configureServer(server) {
      const edgeEnv = server.environments.edge;
      // Dedicated ModuleRunner sandboxed to the target environment
      const runner = createServerModuleRunner(edgeEnv, {
        evaluator: async (url, context) => {
          // Isolated execution frame preventing global scope leakage
          return edgeEnv.runner.runModule(url, context);
        },
      });

      return () => {
        server.middlewares.use(async (req, res, next) => {
          try {
            const mod = await runner.import('/src/entry.edge.ts');
            await mod.render(req, res);
          } catch (err) {
            next(err);
          }
        });
      };
    },
  }],
});
```
Recommended MCP Servers (mcp-serverlist.com)

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

Vite AST & Config Inspector MCP
MCP server providing diagnostic analysis of Vite configuration ASTs and environment dependency graphs.
Recommended Agent Skills (askills.dev)

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

Vite Multi-Runtime Verifier
CLI utility to lint Vite 6 configuration files for deprecated ssrLoadModule calls and shared mutable globals.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Multi-Runtime Context Isolation & Memory Sandboxing

Vite 6 Environment API Multi-Runtime Context Isolation & Memory Sandboxing defines an industrial-grade behavioral standard for frontend engineering. Enforces strict memory, execution context, and global scope isolation when executing heterogeneous SSR pipelines across browser, Node.js, and edge workers via Vite 6 Environment API. Prevents cross-runtime state leakage, globalThis pollution, and invalid shared module cache reuse during concurrent Hot Module Replacement (HMR). 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 Global Scope Contamination and Shared Module Graph Leaks in Multi-Runtime 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 Global Scope Contamination and Shared Module Graph Leaks in Multi-Runtime 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 instantiate dedicated environments via `createDevEnvironment` or target existing environments via `server.environments[name]` rather than legacy `server.ssrLoadModule`.

Engineers MUST ALWAYS instantiate dedicated environments via `createDevEnvironment` or target existing environments via `server.environments[name]` rather than legacy `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.
2

Engineers MUST NOT mutate `globalThis` or process-level globals to share state or provide runtime-specific polyfills across different runtime environments.

Engineers MUST NOT mutate `globalThis` or process-level globals to share state or provide runtime-specific polyfills across different runtime 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

Code MUST isolate execution contexts using Vite 6 `ModuleRunner` with runtime-specific `runnerOptions` (evaluator or VM sandbox) instead of sharing single-context execution.

Code MUST isolate execution contexts using Vite 6 `ModuleRunner` with runtime-specific `runnerOptions` (evaluator or VM sandbox) instead of sharing single-context execution.

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

Custom environments (such as Cloudflare Workers or Node.js) MUST explicitly define isolated `resolve.conditions` and `resolve.externalConditions` to prevent cross-runtime resolution bleed.

Custom environments (such as Cloudflare Workers or Node.js) MUST explicitly define isolated `resolve.conditions` and `resolve.externalConditions` to prevent cross-runtime resolution bleed.

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

HMR listeners and event emitters MUST be bound to `environment.hot` rather than root `server.hot` to prevent runtime dispatch collisions.

HMR listeners and event emitters MUST be bound to `environment.hot` rather than root `server.hot` to prevent runtime dispatch collisions.

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 Context Isolation & Memory Sandboxing critical for AI coding assistants?

Enforces strict memory, execution context, and global scope isolation when executing heterogeneous SSR pipelines across browser, Node.js, and edge workers via Vite 6 Environment API. Prevents cross-runtime state leakage, globalThis pollution, and invalid shared module cache reuse during concurrent Hot Module Replacement (HMR). 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 Global Scope Contamination and Shared Module Graph Leaks in Multi-Runtime 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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