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frontendcritical PriorityID: vite6-environment-api-boundary-isolation-vite-6-environme-747

Vite 6 Environment API Cross-Runtime Boundary Isolation

Enforces strict boundary isolation, module graph partitioning, and target-specific resolution conditions using the Vite 6 Environment API. Prevents silent runtime pollution such as Node.js built-ins leaking into workerd/Cloudflare Workers and synthetic server polyfills inflating browser client bundles.

Prohibited Anti-Pattern: Ambient Node Builtin Leakage and Monolithic SSR Target Conflation in Vite Heterogeneous Builds

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---
description: Vite 6 Environment API Cross-Runtime Boundary Isolation - Enforces strict boundary isolation, module graph partitioning, and target-specific resolution conditions using the Vite 6 Environment API. Prevents silent runtime pollution such as Node.js built-ins leaking into workerd/Cloudflare Workers and synthetic server polyfills inflating browser client bundles.
globs: vite.config.ts, vite.config.*.ts, src/**/*.{ts,tsx}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite6-environment-api-boundary-isolation-vite-6-environme-747"
---

# Vite 6 Environment API Cross-Runtime Boundary Isolation

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Ambient Node Builtin Leakage and Monolithic SSR Target Conflation in Vite Heterogeneous Builds

## System Constraints
You are a Principal Software Architect enforcing Vite 6 Environment API Cross-Runtime Boundary Isolation. You must ensure heterogeneous runtime environments (such as client browsers, Node.js SSR, and workerd edge functions) maintain completely isolated module graphs, custom package export conditions, and target-specific externalization rules without cross-contamination.

## Strict Guidelines
- Engineers MUST ALWAYS configure runtime targets via top-level 'environments' blocks in Vite 6 rather than relying on legacy monolithic 'ssr' or 'build' settings.
- Engineers MUST configure target-specific 'resolve.conditions' (e.g., ['workerd', 'worker'] for Cloudflare Workers vs ['node'] for Node.js) exclusively within their respective environment declarations.
- Vite plugin authors MUST inspect 'this.environment.name' or 'this.environment.mode' inside hooks rather than relying on the legacy binary 'ssr' boolean parameter.
- Engineers MUST NOT rely on ambient Node.js globals (such as 'process.env', 'Buffer', or '__dirname') in universal application code without explicit capability detection or boundary-safe abstraction layers.
- Services sharing isomorphic libraries across environments MUST configure explicit conditional exports in package.json to prevent invalid runtime symbol injection.
- Engineers MUST configure 'resolve.noExternal' per environment to prevent Node.js core polyfills from polluting workerd or browser client bundles.

## Bad vs Good Implementations
### Migrating Legacy Monolithic SSR to Vite 6 Environment API

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Configuring SSR via top-level 'ssr' flags assumes a single, uniform non-client runtime. It forces all dependencies into an edge runtime without distinct conditions, and the plugin hook references Node builtins indiscriminately when 'options.ssr' is true.
```typescript
import { defineConfig } from 'vite';

// ANTI-PATTERN: Vite 5 legacy monolithic SSR config conflates
// Node.js SSR and edge runtimes (workerd), leaking Node builtins
export default defineConfig({
  build: {
    outDir: 'dist/client',
  },
  ssr: {
    target: 'webworker',
    noExternal: true, // Forces all packages into edge bundle, pulling unneeded Node polyfills
  },
  plugins: [{
    name: 'custom-runtime-plugin',
    resolveId(id, importer, options) {
      // Flawed legacy binary flag check
      if (options?.ssr) {
        return 'node:async_hooks'; // Leaks Node API into non-Node SSR runtimes like workerd
      }
    },
  }],
});
```

#### Production Standard (Correct)
> **Standard**: Defines isolated client, edge (workerd), and ssrNode environments with dedicated target resolution conditions and bundling behaviors. Uses 'this.environment.name' to ensure plugins apply appropriate runtime-specific module resolutions.
```typescript
import { defineConfig } from 'vite';

// PRODUCTION INVARIANT: Vite 6 isolated environments per target runtime
export default defineConfig({
  environments: {
    client: {
      build: {
        outDir: 'dist/client',
      },
      resolve: {
        conditions: ['browser', 'import'],
      },
    },
    edge: {
      resolve: {
        conditions: ['workerd', 'worker', 'import'],
        noExternal: ['@app/core', 'itty-router'],
        external: ['cloudflare:workers'],
      },
      build: {
        outDir: 'dist/edge',
      },
    },
    ssrNode: {
      resolve: {
        conditions: ['node', 'import'],
      },
      build: {
        outDir: 'dist/server',
      },
    },
  },
  plugins: [{
    name: 'custom-runtime-plugin',
    resolveId(id) {
      // Invariant: Query execution context via this.environment
      if (this.environment.name === 'ssrNode' && id === 'virtual:context') {
        return '\0node-context-impl';
      }
      if (this.environment.name === 'edge' && id === 'virtual:context') {
        return '\0edge-context-impl';
      }
      return null;
    },
  }],
});
```
Recommended MCP Servers (mcp-serverlist.com)

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

Vite Module Graph & Environment Inspector
Inspects Vite transformed modules and resolved IDs per Environment API module graph.
Recommended Agent Skills (askills.dev)

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

Wrangler Dry-Run Verifier
Validates that workerd deployment bundles contain no unsupported Node.js runtime globals or unresolved specifiers.
Architectural Specification & Invariant Rationale

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

Vite 6 Environment API Cross-Runtime Boundary Isolation defines an industrial-grade behavioral standard for frontend engineering. Enforces strict boundary isolation, module graph partitioning, and target-specific resolution conditions using the Vite 6 Environment API. Prevents silent runtime pollution such as Node.js built-ins leaking into workerd/Cloudflare Workers and synthetic server polyfills inflating browser client bundles. 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: Ambient Node Builtin Leakage and Monolithic SSR Target Conflation in Vite Heterogeneous Builds 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 DriftAmbient Node Builtin Leakage and Monolithic SSR Target Conflation in Vite Heterogeneous BuildsCritical
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 runtime targets via top-level 'environments' blocks in Vite 6 rather than relying on legacy monolithic 'ssr' or 'build' settings.

Engineers MUST ALWAYS configure runtime targets via top-level 'environments' blocks in Vite 6 rather than relying on legacy monolithic 'ssr' or 'build' settings.

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 configure target-specific 'resolve.conditions' (e.g., ['workerd', 'worker'] for Cloudflare Workers vs ['node'] for Node.js) exclusively within their respective environment declarations.

Engineers MUST configure target-specific 'resolve.conditions' (e.g., ['workerd', 'worker'] for Cloudflare Workers vs ['node'] for Node.js) exclusively within their respective environment declarations.

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

Vite plugin authors MUST inspect 'this.environment.name' or 'this.environment.mode' inside hooks rather than relying on the legacy binary 'ssr' boolean parameter.

Vite plugin authors MUST inspect 'this.environment.name' or 'this.environment.mode' inside hooks rather than relying on the legacy binary 'ssr' boolean parameter.

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

Engineers MUST NOT rely on ambient Node.js globals (such as 'process.env', 'Buffer', or '__dirname') in universal application code without explicit capability detection or boundary-safe abstraction layers.

Engineers MUST NOT rely on ambient Node.js globals (such as 'process.env', 'Buffer', or '__dirname') in universal application code without explicit capability detection or boundary-safe abstraction layers.

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

Services sharing isomorphic libraries across environments MUST configure explicit conditional exports in package.json to prevent invalid runtime symbol injection.

Services sharing isomorphic libraries across environments MUST configure explicit conditional exports in package.json to prevent invalid runtime symbol injection.

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

Engineers MUST configure 'resolve.noExternal' per environment to prevent Node.js core polyfills from polluting workerd or browser client bundles.

Engineers MUST configure 'resolve.noExternal' per environment to prevent Node.js core polyfills from polluting workerd or browser client bundles.

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 Boundary Isolation critical for AI coding assistants?

Enforces strict boundary isolation, module graph partitioning, and target-specific resolution conditions using the Vite 6 Environment API. Prevents silent runtime pollution such as Node.js built-ins leaking into workerd/Cloudflare Workers and synthetic server polyfills inflating browser client bundles. 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 (Ambient Node Builtin Leakage and Monolithic SSR Target Conflation in Vite Heterogeneous Builds) 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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