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frontendcritical PriorityID: vite-6-environment-api-runtime-boundary-guardrail

Vite 6 Environment API Custom Runtime Boundary Guardrail

Enforces strict isolation of client, server, and edge module graphs using the Vite 6 Environment API. Prevents cross-target compilation leakage, runtime polyfill bleeding, and secret exposure by scoping transforms, module resolutions, and runtime instances strictly to designated environment runtimes.

Prohibited Anti-Pattern: Cross-Target Module Graph Pollution via Shared Legacy Vite Plugin Contexts

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---
description: Vite 6 Environment API Custom Runtime Boundary Guardrail - Enforces strict isolation of client, server, and edge module graphs using the Vite 6 Environment API. Prevents cross-target compilation leakage, runtime polyfill bleeding, and secret exposure by scoping transforms, module resolutions, and runtime instances strictly to designated environment runtimes.
globs: vite.config.{ts,js,mjs}, plugins/**/*.{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-runtime-boundary-guardrail"
---

# Vite 6 Environment API Custom Runtime Boundary Guardrail

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Cross-Target Module Graph Pollution via Shared Legacy Vite Plugin Contexts

## System Constraints
You are a Principal Software Architect enforcing Vite 6 Environment API Custom Runtime Boundary Guardrails. Mandate strict module graph isolation between client, SSR, and custom runtime environments (e.g., Workerd, Node, Deno). Reject any legacy single-graph workarounds (e.g., relying on global `config.build.ssr` or shared plugin state). Require plugins to operate contextually within `this.environment` and configure discrete environment execution targets with non-leaking module resolution boundaries.

## Strict Guidelines
- Engineers MUST ALWAYS configure discrete environments using the Vite 6 `environments` block (e.g., `client`, `ssr`, `edge`) instead of relying on legacy global flags like `build.ssr`.
- Engineers MUST NOT maintain shared mutable module state across environments inside Vite plugin hooks; plugins MUST access execution context via `this.environment`.
- Custom runtimes MUST use `createViteRuntime` or dedicated environment runners to isolate global scopes (e.g., `window`, `process`, Web APIs) and prevent server-only secrets from bleeding into client module graphs.
- Plugin hooks that perform code transforms, virtual module resolution, or AST rewriting MUST condition behavior explicitly on `this.environment.name` or `this.environment.mode`.
- Components and application code NEVER import from modules belonging to a disjoint environment tier without explicit conditional exports or environment-aware boundaries.

## Bad vs Good Implementations
### Migrating Legacy SSR Plugin to Vite 6 Environment-Aware Plugin

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: The plugin uses global configuration state (`config.build.ssr`) and shared runtime maps, which fails when Vite 6 processes client, server, and edge module graphs concurrently. This allows server-side tokens or client-side mocks to cross-contaminate disparate environment graphs.
```typescript
import { Plugin } from 'vite';

// ANTI-PATTERN: Shared global state and legacy config inspection causes cross-environment leakage
export function legacyAuthPlugin(): Plugin {
  let isSSR = false;
  const sharedResolvedIds = new Map<string, string>();

  return {
    name: 'auth-plugin',
    configResolved(config) {
      // Flawed assumption: Assumes build is binary (client OR ssr globally)
      isSSR = !!config.build.ssr;
    },
    resolveId(id) {
      if (id === 'virtual:auth-config') {
        // Pollutes both module graphs with identical resolution
        const resolved = isSSR ? 'src/auth.server.ts' : 'src/auth.client.ts';
        sharedResolvedIds.set(id, resolved);
        return resolved;
      }
    }
  };
}
```

#### Production Standard (Correct)
> **Standard**: The plugin leverages Vite 6's `this.environment.name` in plugin hooks, producing isolated virtual module payloads specifically tailored to each environment target without leaking server secrets into the client module graph.
```typescript
import { Plugin, EnvironmentOptions } from 'vite';

// PRODUCTION INVARIANT: Per-environment scoped resolution using Vite 6 Environment API
export function environmentIsolatedAuthPlugin(): Plugin {
  return {
    name: 'auth-plugin',
    resolveId(id) {
      if (id !== 'virtual:auth-config') return;

      // Environment boundary inspection via 'this.environment'
      const envName = this.environment.name;

      if (envName === 'client') {
        return '\0virtual:auth-config-client';
      } else if (envName === 'ssr' || envName === 'edge') {
        return '\0virtual:auth-config-server';
      }

      throw new Error(`Unsupported runtime environment: ${envName}`);
    },
    load(id) {
      if (id === '\0virtual:auth-config-client') {
        return 'export const authConfig = { mode: "public", endpoint: "/api/auth" };';
      }
      if (id === '\0virtual:auth-config-server') {
        return 'export const authConfig = { mode: "secure", secret: process.env.AUTH_SECRET };';
      }
    }
  };
}
```

### Configuring Explicit Environment Module Graphs in vite.config.ts

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Monolithic resolution aliases force all targets to share the same Node.js dependencies, leading to runtime failures in edge runtimes (e.g., Cloudflare Workers) or compilation errors when targeting standard browsers.
```typescript
import { defineConfig } from 'vite';

// ANTI-PATTERN: Monolithic configuration with implicit runtime collision
export default defineConfig({
  build: {
    ssr: false
  },
  resolve: {
    // Single shared alias breaks Workerd or Node boundaries
    alias: { '@runtime-compat': 'node:crypto' }
  }
});
```

#### Production Standard (Correct)
> **Standard**: Declares explicit environment targets using Vite 6 `environments`. Each module graph defines unique resolve conditions, output directories, and aliasing boundaries, preventing runtime leakage.
```typescript
import { defineConfig } from 'vite';

// PRODUCTION INVARIANT: Vite 6 declarative multi-environment runtime separation
export default defineConfig({
  environments: {
    client: {
      build: {
        outDir: 'dist/client'
      },
      resolve: {
        conditions: ['browser', 'import']
      }
    },
    ssr: {
      build: {
        outDir: 'dist/server'
      },
      resolve: {
        conditions: ['node', 'import'],
        external: true
      }
    },
    edge: {
      build: {
        outDir: 'dist/edge'
      },
      resolve: {
        conditions: ['workerd', 'worker', 'browser'],
        alias: {
          '@runtime-compat': 'crypto-browserify'
        }
      }
    }
  }
});
```
Recommended MCP Servers (mcp-serverlist.com)

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

AST & Dependency Graph Inspector
Inspects Vite transformed module graphs across environments to detect cross-graph leakage.
Recommended Agent Skills (askills.dev)

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

Vite Environment Graph Auditor
Validates that target exports and virtual modules do not leak between client and server runtimes in Vite 6.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Custom Runtime Boundary Guardrail

Vite 6 Environment API Custom Runtime Boundary Guardrail defines an industrial-grade behavioral standard for frontend engineering. Enforces strict isolation of client, server, and edge module graphs using the Vite 6 Environment API. Prevents cross-target compilation leakage, runtime polyfill bleeding, and secret exposure by scoping transforms, module resolutions, and runtime instances strictly to designated environment runtimes. 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-Target Module Graph Pollution via Shared Legacy Vite Plugin Contexts 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-Target Module Graph Pollution via Shared Legacy Vite Plugin ContextsCritical
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 discrete environments using the Vite 6 `environments` block (e.g., `client`, `ssr`, `edge`) instead of relying on legacy global flags like `build.ssr`.

Engineers MUST ALWAYS configure discrete environments using the Vite 6 `environments` block (e.g., `client`, `ssr`, `edge`) instead of relying on legacy global flags like `build.ssr`.

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 maintain shared mutable module state across environments inside Vite plugin hooks

Engineers MUST NOT maintain shared mutable module state across environments inside Vite plugin hooks; plugins MUST access execution context via `this.environment`.

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 runtimes MUST use `createViteRuntime` or dedicated environment runners to isolate global scopes (e.g., `window`, `process`, Web APIs) and prevent server-only secrets from bleeding into client module graphs.

Custom runtimes MUST use `createViteRuntime` or dedicated environment runners to isolate global scopes (e.g., `window`, `process`, Web APIs) and prevent server-only secrets from bleeding into client 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

Plugin hooks that perform code transforms, virtual module resolution, or AST rewriting MUST condition behavior explicitly on `this.environment.name` or `this.environment.mode`.

Plugin hooks that perform code transforms, virtual module resolution, or AST rewriting MUST condition behavior explicitly on `this.environment.name` or `this.environment.mode`.

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 application code NEVER import from modules belonging to a disjoint environment tier without explicit conditional exports or environment-aware boundaries.

Components and application code NEVER import from modules belonging to a disjoint environment tier without explicit conditional exports or environment-aware boundaries.

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 Custom Runtime Boundary Guardrail critical for AI coding assistants?

Enforces strict isolation of client, server, and edge module graphs using the Vite 6 Environment API. Prevents cross-target compilation leakage, runtime polyfill bleeding, and secret exposure by scoping transforms, module resolutions, and runtime instances strictly to designated environment runtimes. 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-Target Module Graph Pollution via Shared Legacy Vite Plugin Contexts) 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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