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frontendcritical PriorityID: vite-6-environment-api-runtime-segregation

Vite 6 Environment API Runtime Segregation and Boundary Isolation

Enforces strict runtime segregation across client, SSR, and edge environments using Vite 6's Environment API. Prevents cross-runtime contamination, inadvertent leakage of private server-side secrets or Node built-in APIs into browser bundles, and ensures isolated module graphs with distinct resolve conditions.

Prohibited Anti-Pattern: Leaking Server Modules or Secrets to Client Builds via Unified Vite 5-style Configuration

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---
description: Vite 6 Environment API Runtime Segregation and Boundary Isolation - Enforces strict runtime segregation across client, SSR, and edge environments using Vite 6's Environment API. Prevents cross-runtime contamination, inadvertent leakage of private server-side secrets or Node built-in APIs into browser bundles, and ensures isolated module graphs with distinct resolve conditions.
globs: vite.config.{ts,js,mjs}, src/**/*.{ts,tsx,js,jsx}, server/**/*.{ts,js,mjs}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite-6-environment-api-runtime-segregation"
---

# Vite 6 Environment API Runtime Segregation and Boundary Isolation

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Leaking Server Modules or Secrets to Client Builds via Unified Vite 5-style Configuration

## System Constraints
You are a Principal Architect enforcing Vite 6 Environment API standards. Mandate isolated module graphs and environment-specific build configurations for client, SSR, and edge runtimes. Block legacy Vite 5 dual-target single-pipeline hacks, verify export conditions, and prevent Node.js or secret leaks into browser bundles.

## Strict Guidelines
- Engineers MUST ALWAYS configure distinct runtimes using Vite 6's top-level `environments` configuration block (`environments.client`, `environments.ssr`, `environments.edge`) rather than relying on legacy top-level `ssr` build flags.
- Engineers MUST NOT share un-gated plugins or alias transforms across client and server environments if those plugins inject server-only libraries, Node built-ins, or sensitive runtime variables.
- Custom plugins interacting with the build pipeline MUST check `this.environment.name` in plugin hooks (such as `resolveId`, `load`, and `transform`) to restrict actions exclusively to their target runtime.
- Codebases MUST utilize package.json `subpath imports` (e.g., `#env-specific`) or conditional exports mapped to dedicated runtime environments (`browser`, `node`, `edge-light`) to enforce compilation barriers.
- Components and frontend logic NEVER import directly from server-side files; any shared contracts MUST reside in pure isomorphic modules with zero side-effects and zero native runtime imports.

## Bad vs Good Implementations
### Vite Configuration: Legacy Single Pipeline vs. Vite 6 Environment API

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Declaring globals like 'process.env.API_SECRET' at root define leaks sensitive server credentials into the client bundle. Configuring SSR via legacy root flags prevents runtime-specific dependency optimization and module graph isolation.
```typescript
import { defineConfig } from 'vite';
import react from '@vitejs/plugin-react';

// ANTI-PATTERN: Unified configuration with leaky build flags and globally shared defines
export default defineConfig({
  plugins: [react()],
  define: {
    'process.env.API_SECRET': JSON.stringify(process.env.API_SECRET) // Leaked globally to client bundle!
  },
  ssr: {
    noExternal: ['shared-ui']
  },
  build: {
    rollupOptions: {
      external: ['node:fs', 'node:path']
    }
  }
});
```

#### Production Standard (Correct)
> **Standard**: Defines separate module execution environments with runtime-specific resolve conditions and targets. In-memory defines and native externals exist strictly within the SSR environment, shielding the client graph from secret exposure and Node API failures.
```typescript
import { defineConfig } from 'vite';
import react from '@vitejs/plugin-react';

// PRODUCTION STANDARD: Vite 6 Environment API with isolated module graphs
export default defineConfig({
  environments: {
    client: {
      plugins: [react()],
      build: {
        outDir: 'dist/client'
      },
      resolve: {
        conditions: ['browser']
      }
    },
    ssr: {
      build: {
        outDir: 'dist/server'
      },
      resolve: {
        conditions: ['node'],
        external: ['node:fs', 'node:path', 'pg']
      },
      define: {
        'process.env.API_SECRET': JSON.stringify(process.env.API_SECRET)
      }
    }
  }
});
```

### Plugin Hook Isolation via Environment Context

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: The transform hook executes indiscriminately against client, SSR, and worker passes, injecting the database password into the browser-facing bundle.
```typescript
import type { Plugin } from 'vite';

// ANTI-PATTERN: Global transform hook applying server logic across all graphs
export function serverDataInjectionPlugin(): Plugin {
  return {
    name: 'server-data-injector',
    transform(code, id) {
      if (id.includes('runtime-config.ts')) {
        return `export const dbPassword = ${JSON.stringify(process.env.DB_PASS)};\n${code}`;
      }
      return null;
    }
  };
}
```

#### Production Standard (Correct)
> **Standard**: Validates `this.environment.name === 'ssr'` before processing file transformations, ensuring that server-specific code injections never execute within client or web worker environments.
```typescript
import type { Plugin } from 'vite';

// PRODUCTION STANDARD: Restrict plugin hook execution using this.environment.name
export function serverDataInjectionPlugin(): Plugin {
  return {
    name: 'server-data-injector',
    transform(code, id) {
      // Strictly scope transform to the 'ssr' environment
      if (this.environment.name !== 'ssr') {
        return null;
      }
      if (id.includes('runtime-config.server.ts')) {
        return `export const dbPassword = ${JSON.stringify(process.env.DB_PASS)};\n${code}`;
      }
      return null;
    }
  };
}
```
Recommended MCP Servers (mcp-serverlist.com)

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

AST Inspector MCP
Inspects emitted module graphs and ASTs to detect leaky imports and misplaced native modules across boundary files.
Recommended Agent Skills (askills.dev)

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

Vite Bundle Leak Detector
Static analysis check that parses client distribution files to assert absence of sensitive environment variables and server-only node built-ins.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Runtime Segregation and Boundary Isolation

Vite 6 Environment API Runtime Segregation and Boundary Isolation defines an industrial-grade behavioral standard for frontend engineering. Enforces strict runtime segregation across client, SSR, and edge environments using Vite 6's Environment API. Prevents cross-runtime contamination, inadvertent leakage of private server-side secrets or Node built-in APIs into browser bundles, and ensures isolated module graphs with distinct resolve conditions. 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 Server Modules or Secrets to Client Builds via Unified Vite 5-style Configuration 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 Server Modules or Secrets to Client Builds via Unified Vite 5-style ConfigurationCritical
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 runtimes using Vite 6's top-level `environments` configuration block (`environments.client`, `environments.ssr`, `environments.edge`) rather than relying on legacy top-level `ssr` build flags.

Engineers MUST ALWAYS configure distinct runtimes using Vite 6's top-level `environments` configuration block (`environments.client`, `environments.ssr`, `environments.edge`) rather than relying on legacy top-level `ssr` build 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 share un-gated plugins or alias transforms across client and server environments if those plugins inject server-only libraries, Node built-ins, or sensitive runtime variables.

Engineers MUST NOT share un-gated plugins or alias transforms across client and server environments if those plugins inject server-only libraries, Node built-ins, or sensitive runtime variables.

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 plugins interacting with the build pipeline MUST check `this.environment.name` in plugin hooks (such as `resolveId`, `load`, and `transform`) to restrict actions exclusively to their target runtime.

Custom plugins interacting with the build pipeline MUST check `this.environment.name` in plugin hooks (such as `resolveId`, `load`, and `transform`) to restrict actions exclusively to their target runtime.

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

Codebases MUST utilize package.json `subpath imports` (e.g., `#env-specific`) or conditional exports mapped to dedicated runtime environments (`browser`, `node`, `edge-light`) to enforce compilation barriers.

Codebases MUST utilize package.json `subpath imports` (e.g., `#env-specific`) or conditional exports mapped to dedicated runtime environments (`browser`, `node`, `edge-light`) to enforce compilation barriers.

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 frontend logic NEVER import directly from server-side files

Components and frontend logic NEVER import directly from server-side files; any shared contracts MUST reside in pure isomorphic modules with zero side-effects and zero native runtime imports.

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 Runtime Segregation and Boundary Isolation critical for AI coding assistants?

Enforces strict runtime segregation across client, SSR, and edge environments using Vite 6's Environment API. Prevents cross-runtime contamination, inadvertent leakage of private server-side secrets or Node built-in APIs into browser bundles, and ensures isolated module graphs with distinct resolve conditions. 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 Server Modules or Secrets to Client Builds via Unified Vite 5-style Configuration) 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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Vite