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frontendcritical PriorityID: vite6-environment-api-runtime-isolation-vite-6-environme-725

Vite 6 Environment API Multi-Runtime Compilation Boundary Isolation

Enforces strict runtime module boundary isolation across client, SSR Node.js, and edge worker execution contexts using the Vite 6 Environment API. Prevents toxic module leakage such as Node.js built-ins or server secrets bundling into client chunks by mandating explicit per-environment export conditions, isolated Rollup configurations, and environment-aware plugin hooks.

Prohibited Anti-Pattern: Monolithic Multi-Target Compilation and Cross-Environment Module Bleed

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---
description: Vite 6 Environment API Multi-Runtime Compilation Boundary Isolation - Enforces strict runtime module boundary isolation across client, SSR Node.js, and edge worker execution contexts using the Vite 6 Environment API. Prevents toxic module leakage such as Node.js built-ins or server secrets bundling into client chunks by mandating explicit per-environment export conditions, isolated Rollup configurations, and environment-aware plugin hooks.
globs: vite.config.ts, vite.config.*.ts, src/**/*.{ts,tsx,js,jsx}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite6-environment-api-runtime-isolation-vite-6-environme-725"
---

# Vite 6 Environment API Multi-Runtime Compilation Boundary Isolation

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Monolithic Multi-Target Compilation and Cross-Environment Module Bleed

## System Constraints
You are a Principal Software Architect enforcing runtime boundary isolation in Vite 6 using the Environment API. Mandate distinct compilation contexts for client, SSR (Node.js), and edge/workerd runtimes. Block legacy Vite 5 dual-build hacks, un-scoped global aliases, and runtime leakages.

## Strict Guidelines
- Engineers MUST ALWAYS declare runtime environments explicitly under Vite 6 `environments` (e.g., `environments.client`, `environments.ssr`, `environments.edge`) rather than relying on global `build.ssr` toggles.
- Engineers MUST NOT define target-specific `resolve.conditions`, `resolve.externalConditions`, or `resolve.alias` at the global root configuration when targeting heterogeneous runtimes.
- Custom plugins MUST inspect `this.environment.name` inside plugin lifecycle hooks (`resolveId`, `load`, `transform`) to branch runtime behavior rather than checking external build-state flags.
- Build scripts MUST invoke `builder.build(builder.environments[name])` using the Vite 6 Builder API instead of spawning disconnected Vite processes with mutable global environment variables.
- Client environment configurations MUST explicitly exclude server-only packages and Node built-ins using `optimizeDeps.exclude` and Rollup externalization guardrails.
- Components NEVER import server or runtime-specific modules directly; they MUST consume them through environment-isolated entrypoints or virtual module abstractions.

## Bad vs Good Implementations
### Multi-Runtime Configuration using Vite 6 Environment API

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Configuring global conditions and aliases bleeds Node.js imports directly into the client compilation graph. Relying on an ambient process.env flag breaks multi-environment concurrent builds and causes client runtime crashes when resolving server-only built-ins.
```typescript
import { defineConfig } from 'vite';

// ANTI-PATTERN: Global resolution conditions bleed across client and SSR
export default defineConfig({
  resolve: {
    // Leaks node conditions into client compilation graph
    conditions: ['node', 'import'],
    alias: {
      '@env-storage': 'node:fs/promises'
    }
  },
  build: {
    ssr: process.env.BUILD_SSR === 'true'
  }
});
```

#### Production Standard (Correct)
> **Standard**: Explicitly separates compilation graphs into distinct Vite 6 environments. Each environment strictly enforces its own resolution conditions, targets, and output boundaries, eliminating cross-runtime symbol contamination.
```typescript
import { defineConfig } from 'vite';

// PRODUCTION INVARIANT: Isolated environment definitions with dedicated runtimes
export default defineConfig({
  environments: {
    client: {
      build: {
        outDir: 'dist/client',
        sourcemap: true
      },
      resolve: {
        conditions: ['browser', 'module', 'import']
      }
    },
    ssr: {
      build: {
        outDir: 'dist/server',
        target: 'node22',
        ssr: true
      },
      resolve: {
        conditions: ['node', 'import'],
        externalConditions: ['node']
      }
    },
    edge: {
      build: {
        outDir: 'dist/edge',
        ssr: true
      },
      resolve: {
        conditions: ['worker', 'workerd', 'browser']
      }
    }
  }
});
```

### Environment-Aware Vite Plugin Hook

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Vite 6 compiles multiple environments concurrently. Caching `config.build.ssr` into closure scope causes race conditions where client builds may receive server configurations if SSR compilation runs in the same process.
```typescript
import type { Plugin } from 'vite';

// ANTI-PATTERN: Checking global config state inside shared plugin
export function serverSecretPlugin(): Plugin {
  let isSSR = false;
  return {
    name: 'secret-shield',
    configResolved(config) {
      // Shared mutable closure state fails in Vite 6 multi-environment builds
      isSSR = !!config.build.ssr;
    },
    resolveId(id) {
      if (id === 'virtual:runtime-config') {
        return isSSR ? '\0server-config' : '\0client-config';
      }
    }
  };
}
```

#### Production Standard (Correct)
> **Standard**: Utilizes the Vite 6 `this.environment.name` execution context within the plugin hook. This guarantees pure isolation per compilation pass without race conditions or leaks across concurrent multi-environment builds.
```typescript
import type { Plugin } from 'vite';

// PRODUCTION INVARIANT: Querying this.environment for runtime-specific dispatch
export function serverSecretPlugin(): Plugin {
  return {
    name: 'secret-shield',
    resolveId(id) {
      if (id === 'virtual:runtime-config') {
        // this.environment is scoped to the active execution graph
        const envName = this.environment.name;
        if (envName === 'client') {
          return '\0client-config';
        }
        return '\0server-config';
      }
      return null;
    },
    load(id) {
      if (id === '\0client-config') {
        return 'export const config = { runtime: "client", apiBase: "/api" };';
      }
      if (id === '\0server-config') {
        return 'export const config = { runtime: "server", dbSecret: process.env.DB_PASSWORD };';
      }
      return null;
    }
  };
}
```
Recommended MCP Servers (mcp-serverlist.com)

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

Filesystem MCP
Inspects Vite configuration files, dist outputs, and build manifests across environments.
Recommended Agent Skills (askills.dev)

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

Vite Build Analyzer CLI
Validates multi-environment bundle manifests and checks for illicit node:* imports in client chunks.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Multi-Runtime Compilation Boundary Isolation

Vite 6 Environment API Multi-Runtime Compilation Boundary Isolation defines an industrial-grade behavioral standard for frontend engineering. Enforces strict runtime module boundary isolation across client, SSR Node.js, and edge worker execution contexts using the Vite 6 Environment API. Prevents toxic module leakage such as Node.js built-ins or server secrets bundling into client chunks by mandating explicit per-environment export conditions, isolated Rollup configurations, and environment-aware plugin hooks. 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 Multi-Target Compilation and Cross-Environment Module Bleed 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 Multi-Target Compilation and Cross-Environment Module BleedCritical
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 declare runtime environments explicitly under Vite 6 `environments` (e.g., `environments.client`, `environments.ssr`, `environments.edge`) rather than relying on global `build.ssr` toggles.

Engineers MUST ALWAYS declare runtime environments explicitly under Vite 6 `environments` (e.g., `environments.client`, `environments.ssr`, `environments.edge`) rather than relying on global `build.ssr` toggles.

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 define target-specific `resolve.conditions`, `resolve.externalConditions`, or `resolve.alias` at the global root configuration when targeting heterogeneous runtimes.

Engineers MUST NOT define target-specific `resolve.conditions`, `resolve.externalConditions`, or `resolve.alias` at the global root configuration when targeting heterogeneous runtimes.

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 MUST inspect `this.environment.name` inside plugin lifecycle hooks (`resolveId`, `load`, `transform`) to branch runtime behavior rather than checking external build-state flags.

Custom plugins MUST inspect `this.environment.name` inside plugin lifecycle hooks (`resolveId`, `load`, `transform`) to branch runtime behavior rather than checking external build-state 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.
4

Build scripts MUST invoke `builder.build(builder.environments[name])` using the Vite 6 Builder API instead of spawning disconnected Vite processes with mutable global environment variables.

Build scripts MUST invoke `builder.build(builder.environments[name])` using the Vite 6 Builder API instead of spawning disconnected Vite processes with mutable global environment 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.
5

Client environment configurations MUST explicitly exclude server-only packages and Node built-ins using `optimizeDeps.exclude` and Rollup externalization guardrails.

Client environment configurations MUST explicitly exclude server-only packages and Node built-ins using `optimizeDeps.exclude` and Rollup externalization guardrails.

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.
6

Components NEVER import server or runtime-specific modules directly

Components NEVER import server or runtime-specific modules directly; they MUST consume them through environment-isolated entrypoints or virtual module abstractions.

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 Compilation Boundary Isolation critical for AI coding assistants?

Enforces strict runtime module boundary isolation across client, SSR Node.js, and edge worker execution contexts using the Vite 6 Environment API. Prevents toxic module leakage such as Node.js built-ins or server secrets bundling into client chunks by mandating explicit per-environment export conditions, isolated Rollup configurations, and environment-aware plugin hooks. 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 Multi-Target Compilation and Cross-Environment Module Bleed) 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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