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frontendcritical PriorityID: vite6-environment-api-runtime-isolation-vite-6-environme-419

Vite 6 Environment API Cross-Runtime Hydration Isolation Standard

Enforces strict execution-boundary isolation between client, Node.js, workerd, and Bun environments using the Vite 6 Environment API. Prevents runtime-specific global pollution, invalid isomorphic imports, and unvalidated environment state serialization during isomorphic hydration.

Prohibited Anti-Pattern: Leaking Runtime-Specific Globals and Bindings Across Vite 6 Multi-Environment Module Graphs

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---
description: Vite 6 Environment API Cross-Runtime Hydration Isolation Standard - Enforces strict execution-boundary isolation between client, Node.js, workerd, and Bun environments using the Vite 6 Environment API. Prevents runtime-specific global pollution, invalid isomorphic imports, and unvalidated environment state serialization during isomorphic hydration.
globs: vite.config.{ts,js,mjs}, src/**/*.{ts,tsx}, server/**/*.{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-419"
---

# Vite 6 Environment API Cross-Runtime Hydration Isolation Standard

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Leaking Runtime-Specific Globals and Bindings Across Vite 6 Multi-Environment Module Graphs

## System Constraints
You are a Principal Software Architect enforcing the Vite 6 Environment API Cross-Runtime Hydration Isolation standard. Mandate strict isolation between client and server environments (Node.js, Cloudflare workerd, Bun). Reject any code that aliases, exposes, or directly imports host-runtime builtins into isomorphic modules, and ensure hydration transfers strictly contain deterministic, JSON-serializable state devoid of platform handles.

## Strict Guidelines
- Engineers MUST ALWAYS configure distinct target environments using Vite 6 `environments` mapping with explicit `resolve.conditions` tailored to each runtime (e.g., `['node']`, `['workerd', 'worker']`, or `['browser']`).
- Engineers MUST NOT import runtime-exclusive namespaces (`node:*`, `cloudflare:*`, `bun:*`) directly into isomorphic modules traversed by the client environment module graph.
- Code MUST pass runtime bindings (e.g., Cloudflare KV, D1, Node streams) strictly via per-request request contexts, never assigning them to shared module scopes or the isomorphic rendering context.
- Hydration serialization pipelines MUST sanitize and serialize transfer state into plain JSON/safe serialization formats, completely stripped of server runtime handles, file descriptors, or host environment instances.
- Components NEVER execute environment-specific APIs inside isomorphic render bodies; environment-gated side effects MUST execute exclusively inside client-only lifecycle hooks or server-only entry points.

## Bad vs Good Implementations
### Cross-Runtime Environment Isolation in Vite 6 Configuration and SSR Pipeline

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: The configuration uses legacy Vite SSR options rather than the Vite 6 Environment API, blinding the compiler to runtime boundaries. Inlining `process.env` contaminates non-Node runtimes (`workerd`), while directly referencing `node:fs` within an isomorphic component breaks client bundle generation and crashes during edge runtime execution.
```typescript
import { defineConfig } from 'vite';
import fs from 'node:fs';

// ANTI-PATTERN: Single SSR pipeline conflating Node.js and workerd runtimes
// causing Node.js module leakage into edge workers and client hydration graphs.
export default defineConfig({
  ssr: {
    noExternal: true,
    target: 'node',
  },
  define: {
    'process.env': process.env,
    __KV_STORAGE__: 'globalThis.MY_KV',
  },
});

// In isomorphic component:
export function UserProfile({ id }: { id: string }) {
  // Leaking runtime check that crashes in workerd / browser
  const isNode = typeof process !== 'undefined' && process.versions != null;
  if (isNode) {
    const data = fs.readFileSync(`/data/${id}.json`, 'utf-8');
    return <div>{data}</div>;
  }
  return <div>Client/Edge View</div>;
}
```

#### Production Standard (Correct)
> **Standard**: Employs the Vite 6 Environment API to create disjoint module resolution graphs with distinct resolve conditions for `client`, `ssr` (Node.js), and `workerd`. Runtime-specific data retrieval is completely decoupled from the isomorphic React tree, accepting serialized data via a standard `ServerContext` contract.
```typescript
import { defineConfig } from 'vite';
import { createWorkerdEnvironment } from 'vite-environment-workerd';

// PRODUCTION FIX: Vite 6 Environment API with isolated module graphs and condition separation
export default defineConfig({
  environments: {
    client: {
      build: { outDir: 'dist/client' },
      resolve: { conditions: ['browser'] },
    },
    ssr: {
      build: { outDir: 'dist/ssr' },
      resolve: { conditions: ['node', 'import'] },
    },
    workerd: createWorkerdEnvironment({
      resolve: { conditions: ['workerd', 'worker', 'import'] },
    }),
  },
});

// Safe Isomorphic Boundary: Dependency injection via standard server context
export interface ServerContext {
  userId: string;
  userData: Record<string, unknown> | null;
}

export function UserProfile({ context }: { context?: ServerContext }) {
  // Pure, deterministic isomorphic render using normalized props
  const user = context?.userData ?? null;
  return (
    <div data-testid="user-profile">
      {user ? <pre>{JSON.stringify(user)}</pre> : <span>Loading or Client Fallback</span>}
    </div>
  );
}
```
Recommended MCP Servers (mcp-serverlist.com)

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

Vite Runtime Inspector MCP
Inspects Vite 6 environment module graphs and flags illegal cross-boundary runtime imports.
Recommended Agent Skills (askills.dev)

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

Vite Environment API Linter
Validates Vite configuration compliance and ensures strict environment module boundaries.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Cross-Runtime Hydration Isolation Standard

Vite 6 Environment API Cross-Runtime Hydration Isolation Standard defines an industrial-grade behavioral standard for frontend engineering. Enforces strict execution-boundary isolation between client, Node.js, workerd, and Bun environments using the Vite 6 Environment API. Prevents runtime-specific global pollution, invalid isomorphic imports, and unvalidated environment state serialization during isomorphic hydration. 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: Leaking Runtime-Specific Globals and Bindings Across Vite 6 Multi-Environment Module Graphs 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 DriftLeaking Runtime-Specific Globals and Bindings Across Vite 6 Multi-Environment Module GraphsCritical
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 target environments using Vite 6 `environments` mapping with explicit `resolve.conditions` tailored to each runtime (e.g., `['node']`, `['workerd', 'worker']`, or `['browser']`).

Engineers MUST ALWAYS configure distinct target environments using Vite 6 `environments` mapping with explicit `resolve.conditions` tailored to each runtime (e.g., `['node']`, `['workerd', 'worker']`, or `['browser']`).

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 import runtime-exclusive namespaces (`node

Engineers MUST NOT import runtime-exclusive namespaces (`node:*`, `cloudflare:*`, `bun:*`) directly into isomorphic modules traversed by the client environment module graph.

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 pass runtime bindings (e.g., Cloudflare KV, D1, Node streams) strictly via per-request request contexts, never assigning them to shared module scopes or the isomorphic rendering context.

Code MUST pass runtime bindings (e.g., Cloudflare KV, D1, Node streams) strictly via per-request request contexts, never assigning them to shared module scopes or the isomorphic rendering context.

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

Hydration serialization pipelines MUST sanitize and serialize transfer state into plain JSON/safe serialization formats, completely stripped of server runtime handles, file descriptors, or host environment instances.

Hydration serialization pipelines MUST sanitize and serialize transfer state into plain JSON/safe serialization formats, completely stripped of server runtime handles, file descriptors, or host environment instances.

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 NEVER execute environment-specific APIs inside isomorphic render bodies

Components NEVER execute environment-specific APIs inside isomorphic render bodies; environment-gated side effects MUST execute exclusively inside client-only lifecycle hooks or server-only entry points.

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 Cross-Runtime Hydration Isolation Standard critical for AI coding assistants?

Enforces strict execution-boundary isolation between client, Node.js, workerd, and Bun environments using the Vite 6 Environment API. Prevents runtime-specific global pollution, invalid isomorphic imports, and unvalidated environment state serialization during isomorphic hydration. 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 (Leaking Runtime-Specific Globals and Bindings Across Vite 6 Multi-Environment Module Graphs) 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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