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frontendcritical PriorityID: vite6-multi-environment-module-isolation-guardrail

Vite 6 Multi-Environment Module Isolation & Runtime Boundary Guardrail

Enforces strict module boundary isolation across heterogeneous runtimes (Client, Node SSR, and Edge/Workerd) using the Vite 6 Environment API. Prevents runtime-specific API pollution, accidental credential leakage, and invalid cross-environment module evaluation across decoupled compilation matrices.

Prohibited Anti-Pattern: Cross-Environment Module Bleed and Dynamic Dual-Runtime Imports across Heterogeneous Matrices

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---
description: Vite 6 Multi-Environment Module Isolation & Runtime Boundary Guardrail - Enforces strict module boundary isolation across heterogeneous runtimes (Client, Node SSR, and Edge/Workerd) using the Vite 6 Environment API. Prevents runtime-specific API pollution, accidental credential leakage, and invalid cross-environment module evaluation across decoupled compilation matrices.
globs: vite.config.ts, src/**/*.{ts,tsx}, server/**/*.{ts,tsx}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite6-multi-environment-module-isolation-guardrail"
---

# Vite 6 Multi-Environment Module Isolation & Runtime Boundary Guardrail

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Cross-Environment Module Bleed and Dynamic Dual-Runtime Imports across Heterogeneous Matrices

## System Constraints
You are a Principal Software Architect enforcing Vite 6 Environment API invariants. Mandate strict module boundaries, isolated transform pipelines, and runtime-specific condition separation between Client, Node SSR, and Edge worker environments. Block conditional cross-runtime code-splitting that leaks server tokens or relies on dynamic runtime shims.

## Strict Guidelines
- Engineers MUST ALWAYS configure distinct environment configurations via `environments` in `vite.config.ts` (e.g., `client`, `ssr`, `edge`) instead of relying on deprecated global boolean `ssr` flags.
- Engineers MUST NOT use runtime guards like `typeof window === 'undefined'` or `typeof process !== 'undefined'` to branch imports between client and server runtimes; module boundaries MUST be resolved at compile-time via export conditions or distinct entry graphs.
- Code SHOULD enforce package.json subpath imports (`#runtime/*`) configured against environment-specific `resolve.conditions` (e.g., `node`, `worker`, `browser`) to resolve runtime-appropriate implementations.
- Services MUST NEVER export secrets, server database instances, or Node-exclusive primitives (`node:fs`, `node:net`) from files reachable by the `client` environment graph.
- Components NEVER import server actions or edge runtime loaders directly into client bundle trees without intermediate proxy RPC or boundary markers.

## Bad vs Good Implementations
### Module Boundary Configuration in vite.config.ts

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Configuring unified resolve rules and blanket process.env definitions causes server tokens to leak into client bundles and breaks compilation when bundling for non-Node Edge runtimes like Cloudflare Workers or WinterCG.
```typescript
import { defineConfig } from 'vite';

// ANTI-PATTERN: Unified build with legacy SSR flag leaking Node-specific resolution into edge/client
export default defineConfig({
  ssr: {
    noExternal: ['shared-lib'],
  },
  resolve: {
    alias: {
      '#runtime': './src/runtime/node.ts', // Forces Node runtime for all consumers
    },
  },
  define: {
    'process.env': process.env, // Leaks entire server environment into client bundles
  },
});
```

#### Production Standard (Correct)
> **Standard**: Defines explicit compilation environments with dedicated export conditions and external resolution targets, ensuring browser, Node, and edge targets compile cleanly without shared ambient contamination.
```typescript
import { defineConfig } from 'vite';

// INVARIANT FIX: Leverage Vite 6 Multi-Environment API with strictly scoped runtime pipelines
export default defineConfig({
  environments: {
    client: {
      build: {
        outDir: 'dist/client',
      },
      resolve: {
        conditions: ['browser', 'default'],
      },
    },
    ssr: {
      build: {
        outDir: 'dist/ssr',
      },
      resolve: {
        conditions: ['node', 'default'],
        external: ['node:*'],
      },
    },
    edge: {
      build: {
        outDir: 'dist/edge',
      },
      resolve: {
        conditions: ['workerd', 'worker', 'default'],
        noExternal: true,
      },
    },
  },
});
```

### Subpath Pattern Resolution vs Runtime Dynamic Branching

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Bundlers crawl static ES import statements regardless of runtime `if` conditions, causing `node:fs` to be linked into client chunks, triggering unresolvable runtime errors.
```typescript
// ANTI-PATTERN: Dynamic runtime sniffing causing bundler to pull server symbols into client graph
import * as fs from 'node:fs';

export function readConfig(path: string): string {
  if (typeof window === 'undefined') {
    return fs.readFileSync(path, 'utf8');
  }
  return localStorage.getItem(path) ?? '';
}
```

#### Production Standard (Correct)
> **Standard**: Decouples implementations across environment boundaries via package subpath imports, preventing dead-code pollution and cross-runtime linkage bugs.
```typescript
// INVARIANT FIX: Abstracted through environment-conditioned subpath import '#config-loader'
import { loadConfigValue } from '#config-loader';

export function readConfig(key: string): string {
  return loadConfigValue(key);
}

// src/loader/browser.ts (resolved via 'browser' condition):
// export function loadConfigValue(k: string) { return localStorage.getItem(k) ?? ''; }

// src/loader/node.ts (resolved via 'node' condition):
// import { readFileSync } from 'node:fs';
// export function loadConfigValue(k: string) { return readFileSync(k, 'utf8'); }
```
Recommended MCP Servers (mcp-serverlist.com)

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

Vite Environment Inspector MCP
Inspects Vite 6 environment module graphs and flags illegal cross-boundary imports and leaked server symbols.
Recommended Agent Skills (askills.dev)

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

Vite Module Boundary Linter
CLI tool to statically audit export conditions and verify subpath mapping isolation across Client, SSR, and Edge matrices.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Multi-Environment Module Isolation & Runtime Boundary Guardrail

Vite 6 Multi-Environment Module Isolation & Runtime Boundary Guardrail defines an industrial-grade behavioral standard for frontend engineering. Enforces strict module boundary isolation across heterogeneous runtimes (Client, Node SSR, and Edge/Workerd) using the Vite 6 Environment API. Prevents runtime-specific API pollution, accidental credential leakage, and invalid cross-environment module evaluation across decoupled compilation matrices. 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-Environment Module Bleed and Dynamic Dual-Runtime Imports across Heterogeneous Matrices 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-Environment Module Bleed and Dynamic Dual-Runtime Imports across Heterogeneous MatricesCritical
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 environment configurations via `environments` in `vite.config.ts` (e.g., `client`, `ssr`, `edge`) instead of relying on deprecated global boolean `ssr` flags.

Engineers MUST ALWAYS configure distinct environment configurations via `environments` in `vite.config.ts` (e.g., `client`, `ssr`, `edge`) instead of relying on deprecated global boolean `ssr` 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.
2

Engineers MUST NOT use runtime guards like `typeof window === 'undefined'` or `typeof process !== 'undefined'` to branch imports between client and server runtimes

Engineers MUST NOT use runtime guards like `typeof window === 'undefined'` or `typeof process !== 'undefined'` to branch imports between client and server runtimes; module boundaries MUST be resolved at compile-time via export conditions or distinct entry 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.
3

Code SHOULD enforce package.json subpath imports (`#runtime/*`) configured against environment-specific `resolve.conditions` (e.g., `node`, `worker`, `browser`) to resolve runtime-appropriate implementations.

Code SHOULD enforce package.json subpath imports (`#runtime/*`) configured against environment-specific `resolve.conditions` (e.g., `node`, `worker`, `browser`) to resolve runtime-appropriate implementations.

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

Services MUST NEVER export secrets, server database instances, or Node-exclusive primitives (`node

Services MUST NEVER export secrets, server database instances, or Node-exclusive primitives (`node:fs`, `node:net`) from files reachable by the `client` environment graph.

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 NEVER import server actions or edge runtime loaders directly into client bundle trees without intermediate proxy RPC or boundary markers.

Components NEVER import server actions or edge runtime loaders directly into client bundle trees without intermediate proxy RPC or boundary markers.

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 Multi-Environment Module Isolation & Runtime Boundary Guardrail critical for AI coding assistants?

Enforces strict module boundary isolation across heterogeneous runtimes (Client, Node SSR, and Edge/Workerd) using the Vite 6 Environment API. Prevents runtime-specific API pollution, accidental credential leakage, and invalid cross-environment module evaluation across decoupled compilation matrices. 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-Environment Module Bleed and Dynamic Dual-Runtime Imports across Heterogeneous Matrices) 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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