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frontendcritical PriorityID: vite-6-environment-api-cross-runtime-isolation-invariant

Vite 6 Environment API Strict Cross-Runtime Module Isolation Guardrail

Enforces architectural boundary isolation across heterogeneous runtime environments (browser, node, workerd, edge) using the Vite 6 Environment API. Prevents cross-contamination of runtime-specific module graphs, accidental leaking of Node/Edge primitives into browser bundles, and leaky module resolution during unified multi-target SSR builds.

Prohibited Anti-Pattern: Cross-Runtime Graph Contamination and Deprecated Monolithic SSR Configuration in Vite 6

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---
description: Vite 6 Environment API Strict Cross-Runtime Module Isolation Guardrail - Enforces architectural boundary isolation across heterogeneous runtime environments (browser, node, workerd, edge) using the Vite 6 Environment API. Prevents cross-contamination of runtime-specific module graphs, accidental leaking of Node/Edge primitives into browser bundles, and leaky module resolution during unified multi-target SSR builds.
globs: vite.config.{ts,js,mjs}, src/**/*.{ts,tsx}, server/**/*.{ts,tsx}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite-6-environment-api-cross-runtime-isolation-invariant"
---

# Vite 6 Environment API Strict Cross-Runtime Module Isolation Guardrail

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Cross-Runtime Graph Contamination and Deprecated Monolithic SSR Configuration in Vite 6

## System Constraints
You are a Principal Architect enforcing the Vite 6 Environment API Cross-Runtime Module Isolation Invariant. Vite 6 decouples monolithic SSR processing into discrete, isolated DevEnvironment and BuildEnvironment instances (such as 'client', 'ssr', 'edge', and 'workerd'). You must strictly prevent cross-runtime pollution, prohibit the use of deprecated monolithic options (e.g., options.ssr in plugin hooks), mandate environment-scoped module graphs (this.environment.moduleGraph), and guarantee that runtime-specific dependencies are physically partitioned at configuration and import boundaries.

## Strict Guidelines
- Engineers MUST ALWAYS configure distinct target runtimes via `environments.<name>` in Vite 6 configuration rather than legacy monolithic top-level `ssr` configurations.
- Engineers MUST ALWAYS access runtime state and module graphs via `this.environment` inside Vite plugins, replacing all legacy usages of `options?.ssr` and `server.moduleGraph`.
- Engineers MUST NOT import Node.js built-ins (`node:*`), Cloudflare primitives (`cloudflare:*`), or server-only dependencies into client environment graphs.
- Code SHOULD enforce runtime boundary separation via `package.json` subpath exports with explicit condition sets (`worker`, `node`, `browser`, `default`) instead of dynamic runtime checks (`typeof window !== 'undefined'`).
- Plugins MUST verify `this.environment.name` before executing runtime-specific transforms or injection routines.
- Components NEVER import environment-mismatched singletons across client, edge, and SSR runtime graphs.

## Bad vs Good Implementations
### Vite 6 Plugin Environment-Scoped Resolution

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Accessing `options.ssr` ignores Vite 6's multi-environment architecture where SSR can mean Node.js, Cloudflare Workers, or Fastly Compute. Accessing the monolithic module graph leads to cache poisoning across different targets.
```typescript
import { Plugin } from 'vite';

export function leakyEnvironmentPlugin(): Plugin {
  return {
    name: 'leaky-env-plugin',
    resolveId(id, importer, options) {
      // VIOLATION: Relying on deprecated monolithic options.ssr
      // Leaks module resolution across Edge and Browser worker graphs
      if (options?.ssr) {
        if (id === 'virtual:runtime-adapter') {
          return '\0node-runtime-adapter';
        }
      }
      return null;
    },
    transform(code, id) {
      // VIOLATION: Accessing global server.moduleGraph instead of the active environment
      // const node = this.server?.moduleGraph.getModuleById(id);
      return null;
    }
  };
}
```

#### Production Standard (Correct)
> **Standard**: Utilizes `this.environment.name` in Vite 6, ensuring each environment receives strictly isolated, runtime-compatible implementations without module graph cross-contamination.
```typescript
import { Plugin } from 'vite';

export function isolatedEnvironmentPlugin(): Plugin {
  return {
    name: 'isolated-env-plugin',
    resolveId(id, importer) {
      // INVARIANT: Determine resolution strictly via this.environment.name
      if (id === 'virtual:runtime-adapter') {
        if (this.environment.name === 'edge' || this.environment.name === 'workerd') {
          return '\0edge-runtime-adapter';
        }
        if (this.environment.name === 'ssr') {
          return '\0node-runtime-adapter';
        }
        return '\0browser-runtime-adapter';
      }
      return null;
    },
    load(id) {
      // INVARIANT: Scoped virtual module generation per isolated environment graph
      if (id === '\0edge-runtime-adapter') {
        return 'export const runtime = "edge"; export const storage = null;';
      }
      if (id === '\0node-runtime-adapter') {
        return 'import { AsyncLocalStorage } from "node:async_hooks"; export const runtime = "node"; export const storage = new AsyncLocalStorage();';
      }
      if (id === '\0browser-runtime-adapter') {
        return 'export const runtime = "browser"; export const storage = null;';
      }
      return null;
    }
  };
}
```

### Unified Multi-Target Configuration with Vite 6 Environments

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Top-level `resolve.conditions` and deprecated `ssr` top-level keys force identical resolution rules across both client and server bundles, causing edge-specific packages to bleed into the client bundle or browser-only APIs to bleed into edge workers.
```typescript
import { defineConfig } from 'vite';

// VIOLATION: Monolithic SSR and top-level resolve conditions leaking runtime targets
export default defineConfig({
  ssr: {
    noExternal: ['shared-lib'],
    target: 'webworker' // Leaks webworker conditions into client build
  },
  resolve: {
    conditions: ['worker'] // Global conditions poison both browser and SSR builds
  }
});
```

#### Production Standard (Correct)
> **Standard**: Explicitly declares isolated environment blocks for client, edge, and SSR. Each maintains an independent module graph, externalization policy, and export conditions matching its native runtime.
```typescript
import { defineConfig } from 'vite';

export default defineConfig({
  // INVARIANT: Vite 6 Environment API explicit multi-runtime isolation
  environments: {
    client: {
      build: {
        outDir: 'dist/client'
      },
      resolve: {
        conditions: ['browser', 'import']
      }
    },
    edge: {
      build: {
        outDir: 'dist/edge',
        rollupOptions: {
          input: 'src/entry-edge.ts'
        }
      },
      resolve: {
        conditions: ['worker', 'edge-routine', 'import'],
        noExternal: true
      }
    },
    ssr: {
      build: {
        outDir: 'dist/ssr',
        rollupOptions: {
          input: 'src/entry-node.ts'
        }
      },
      resolve: {
        conditions: ['node', 'import'],
        external: ['node:*']
      }
    }
  }
});
```
Recommended MCP Servers (mcp-serverlist.com)

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

Model Context Protocol Filesystem Server
Inspect and validate file structures across multi-target SSR build outputs and package.json export conditions.
Recommended Agent Skills (askills.dev)

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

Vite 6 Environment AST Validator
Validates plugin hooks to prevent usage of options.ssr and enforce this.environment module graph scoping.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Strict Cross-Runtime Module Isolation Guardrail

Vite 6 Environment API Strict Cross-Runtime Module Isolation Guardrail defines an industrial-grade behavioral standard for frontend engineering. Enforces architectural boundary isolation across heterogeneous runtime environments (browser, node, workerd, edge) using the Vite 6 Environment API. Prevents cross-contamination of runtime-specific module graphs, accidental leaking of Node/Edge primitives into browser bundles, and leaky module resolution during unified multi-target SSR builds. 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-Runtime Graph Contamination and Deprecated Monolithic SSR Configuration in Vite 6 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-Runtime Graph Contamination and Deprecated Monolithic SSR Configuration in Vite 6Critical
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 runtimes via `environments.<name>` in Vite 6 configuration rather than legacy monolithic top-level `ssr` configurations.

Engineers MUST ALWAYS configure distinct target runtimes via `environments.<name>` in Vite 6 configuration rather than legacy monolithic top-level `ssr` configurations.

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 ALWAYS access runtime state and module graphs via `this.environment` inside Vite plugins, replacing all legacy usages of `options?.ssr` and `server.moduleGraph`.

Engineers MUST ALWAYS access runtime state and module graphs via `this.environment` inside Vite plugins, replacing all legacy usages of `options?.ssr` and `server.moduleGraph`.

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

Engineers MUST NOT import Node.js built-ins (`node

Engineers MUST NOT import Node.js built-ins (`node:*`), Cloudflare primitives (`cloudflare:*`), or server-only dependencies into client environment 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

Code SHOULD enforce runtime boundary separation via `package.json` subpath exports with explicit condition sets (`worker`, `node`, `browser`, `default`) instead of dynamic runtime checks (`typeof window !== 'undefined'`).

Code SHOULD enforce runtime boundary separation via `package.json` subpath exports with explicit condition sets (`worker`, `node`, `browser`, `default`) instead of dynamic runtime checks (`typeof window !== 'undefined'`).

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

Plugins MUST verify `this.environment.name` before executing runtime-specific transforms or injection routines.

Plugins MUST verify `this.environment.name` before executing runtime-specific transforms or injection routines.

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 environment-mismatched singletons across client, edge, and SSR runtime graphs.

Components NEVER import environment-mismatched singletons across client, edge, and SSR runtime 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.
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 Strict Cross-Runtime Module Isolation Guardrail critical for AI coding assistants?

Enforces architectural boundary isolation across heterogeneous runtime environments (browser, node, workerd, edge) using the Vite 6 Environment API. Prevents cross-contamination of runtime-specific module graphs, accidental leaking of Node/Edge primitives into browser bundles, and leaky module resolution during unified multi-target SSR builds. 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-Runtime Graph Contamination and Deprecated Monolithic SSR Configuration in Vite 6) 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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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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