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frontendcritical PriorityID: vite-6-environment-api-isolation-boundary

Vite 6 Environment API Multi-Runtime Isolation Boundary

Enforces strict isolation of module graphs, resolution conditions, and transform pipelines across Edge, Node, and Workerd runtimes using the Vite 6 Environment API. Prevents cross-runtime symbol pollution, conflicting export conditions, and shared transform state in unified multi-target SSR compilations.

Prohibited Anti-Pattern: Collapsing multi-target SSR compilation into a monolithic SSR pipeline with shared resolution conditions and cross-polluted transforms

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---
description: Vite 6 Environment API Multi-Runtime Isolation Boundary - Enforces strict isolation of module graphs, resolution conditions, and transform pipelines across Edge, Node, and Workerd runtimes using the Vite 6 Environment API. Prevents cross-runtime symbol pollution, conflicting export conditions, and shared transform state in unified multi-target SSR compilations.
globs: vite.config.{ts,js,mjs}, 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-isolation-boundary"
---

# Vite 6 Environment API Multi-Runtime Isolation Boundary

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Collapsing multi-target SSR compilation into a monolithic SSR pipeline with shared resolution conditions and cross-polluted transforms

## System Constraints
You are a Principal Software Architect enforcing deterministic runtime isolation in Vite 6 multi-target SSR architectures. Mandate strict environment segregation between Client, Node, and WebWorker/Workerd runtime graphs. Ensure Vite 6 Environment API constructs (such as dedicated environment resolution conditions, isolated module graphs, and environment-scoped plugin hooks) are systematically implemented to prevent runtime target leaks.

## Strict Guidelines
- Engineers MUST ALWAYS configure distinct target environments (e.g., `client`, `ssr`, `edge`, `workerd`) within the top-level `environments` configuration block in Vite 6.
- Engineers MUST declare explicit, non-overlapping `resolve.conditions` for each runtime environment (e.g., `['node', 'import']` for Node SSR vs `['workerd', 'worker', 'browser']` for Cloudflare Workers).
- Plugins MUST NOT share mutable compilation caches or module transform state across different environment instances without partitioning by `environment.name`.
- Plugins executing target-specific transforms MUST implement the Vite 6 `applyToEnvironment(environment)` hook or evaluate `this.environment.name` inside lifecycle hooks.
- Engineers MUST NEVER bundle Node.js core modules (`node:fs`, `node:net`, `node:child_process`) into Edge or Workerd target graphs without checking `environment.config.resolve.noExternal` boundaries.
- Components and server handlers MUST NOT rely on ambiguous runtime globals; runtime-specific bindings must be resolved deterministically through the corresponding environment module loader.

## Bad vs Good Implementations
### Monolithic SSR Configuration vs. Vite 6 Isolated Environment Boundary

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Mixing 'workerd' and 'node' in a single shared SSR resolution condition creates non-deterministic module resolution order. A package with distinct 'workerd' and 'node' export paths will arbitrarily pick whichever condition appears first, polluting the other runtime and causing bundling failures. The plugin also applies mutations globally without scoping to the intended environment runtime.
```typescript
import { defineConfig } from 'vite';

// ANTI-PATTERN: Vite 5 monolithic SSR configuration attempting to serve
// both Node and Cloudflare Workerd by mixing export conditions and shared transforms
export default defineConfig({
  ssr: {
    // Shared conditions cause Node dependencies to leak into the Edge bundle
    // or Worker-specific packages to fail resolution in Node SSR tests
    resolve: {
      conditions: ['workerd', 'node', 'import']
    },
    noExternal: true
  },
  plugins: [
    {
      name: 'shared-runtime-transform',
      transform(code, id) {
        // Flaw: Transforms indiscriminately without knowing which runtime targets this file
        if (code.includes('process.env.KV_BINDING')) {
          return code.replace('process.env.KV_BINDING', 'globalThis.__KV__');
        }
      }
    }
  ]
});
```

#### Production Standard (Correct)
> **Standard**: Vite 6's Environment API partitions `ssr` (Node) and `workerd` (Edge) into distinct compilation targets with dedicated module graphs and independent resolution conditions. The custom plugin safely uses `applyToEnvironment` so its transforms execute only when compiling for the Workerd target, eliminating cross-environment state and symbol contamination.
```typescript
import { defineConfig, type Plugin } from 'vite';

// PRODUCTION FIX: Explicit Vite 6 Environment API isolation
const workerdTransformPlugin = (): Plugin => ({
  name: 'workerd-isolated-transform',
  // Scopes this plugin exclusively to the 'workerd' environment
  applyToEnvironment(environment) {
    return environment.name === 'workerd';
  },
  transform(code) {
    return code.replaceAll('process.env.KV_BINDING', 'globalThis.__KV__');
  }
});

export default defineConfig({
  environments: {
    client: {
      build: {
        outDir: 'dist/client'
      }
    },
    ssr: {
      // Node.js SSR runtime boundary
      resolve: {
        conditions: ['node', 'import', 'default'],
        external: true
      },
      build: {
        outDir: 'dist/node-ssr'
      }
    },
    workerd: {
      // Cloudflare Workerd edge runtime boundary
      resolve: {
        conditions: ['workerd', 'worker', 'browser'],
        noExternal: true
      },
      build: {
        outDir: 'dist/workerd',
        target: 'es2022'
      }
    }
  },
  plugins: [workerdTransformPlugin()]
});
```
Recommended MCP Servers (mcp-serverlist.com)

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

Vite Dev Inspector MCP
Inspects Vite Environment module graphs, resolving aliases and conditional export graphs across active runtime environments.
Recommended Agent Skills (askills.dev)

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

Vite Multi-Target Build Runner
Validates and executes Vite 6 multi-environment builds across Node and Edge targets with strict resolution diagnostics.
Architectural Specification & Invariant Rationale

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

Vite 6 Environment API Multi-Runtime Isolation Boundary defines an industrial-grade behavioral standard for frontend engineering. Enforces strict isolation of module graphs, resolution conditions, and transform pipelines across Edge, Node, and Workerd runtimes using the Vite 6 Environment API. Prevents cross-runtime symbol pollution, conflicting export conditions, and shared transform state in unified multi-target SSR compilations. 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: Collapsing multi-target SSR compilation into a monolithic SSR pipeline with shared resolution conditions and cross-polluted transforms 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 DriftCollapsing multi-target SSR compilation into a monolithic SSR pipeline with shared resolution conditions and cross-polluted transformsCritical
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 (e.g., `client`, `ssr`, `edge`, `workerd`) within the top-level `environments` configuration block in Vite 6.

Engineers MUST ALWAYS configure distinct target environments (e.g., `client`, `ssr`, `edge`, `workerd`) within the top-level `environments` configuration block in Vite 6.

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 declare explicit, non-overlapping `resolve.conditions` for each runtime environment (e.g., `['node', 'import']` for Node SSR vs `['workerd', 'worker', 'browser']` for Cloudflare Workers).

Engineers MUST declare explicit, non-overlapping `resolve.conditions` for each runtime environment (e.g., `['node', 'import']` for Node SSR vs `['workerd', 'worker', 'browser']` for Cloudflare Workers).

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

Plugins MUST NOT share mutable compilation caches or module transform state across different environment instances without partitioning by `environment.name`.

Plugins MUST NOT share mutable compilation caches or module transform state across different environment instances without partitioning by `environment.name`.

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

Plugins executing target-specific transforms MUST implement the Vite 6 `applyToEnvironment(environment)` hook or evaluate `this.environment.name` inside lifecycle hooks.

Plugins executing target-specific transforms MUST implement the Vite 6 `applyToEnvironment(environment)` hook or evaluate `this.environment.name` inside lifecycle hooks.

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

Engineers MUST NEVER bundle Node.js core modules (`node

Engineers MUST NEVER bundle Node.js core modules (`node:fs`, `node:net`, `node:child_process`) into Edge or Workerd target graphs without checking `environment.config.resolve.noExternal` 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.
6

Components and server handlers MUST NOT rely on ambiguous runtime globals

Components and server handlers MUST NOT rely on ambiguous runtime globals; runtime-specific bindings must be resolved deterministically through the corresponding environment module loader.

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 Isolation Boundary critical for AI coding assistants?

Enforces strict isolation of module graphs, resolution conditions, and transform pipelines across Edge, Node, and Workerd runtimes using the Vite 6 Environment API. Prevents cross-runtime symbol pollution, conflicting export conditions, and shared transform state in unified multi-target SSR compilations. 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 (Collapsing multi-target SSR compilation into a monolithic SSR pipeline with shared resolution conditions and cross-polluted transforms) 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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