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frontendcritical PriorityID: vite-6-environment-api-runtime-boundary-standard

Strict Multi-Runtime Module Resolution Boundary via Vite 6 Environment API

Enforces complete structural isolation between Edge, Node.js (SSR), and Client (Browser) module graphs using Vite 6's Environment API. Eliminates silent runtime symbol leaks, unintended secret exposure, and browser bundling failures caused by sharing untyped runtime-agnostic module paths. Mandates explicit environment conditions, separated module instances, and zero cross-runtime direct imports.

Prohibited Anti-Pattern: Cross-Runtime Symbol Contamination via Shared Module Graphs in Vite SSR Pipelines

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---
description: Strict Multi-Runtime Module Resolution Boundary via Vite 6 Environment API - Enforces complete structural isolation between Edge, Node.js (SSR), and Client (Browser) module graphs using Vite 6's Environment API. Eliminates silent runtime symbol leaks, unintended secret exposure, and browser bundling failures caused by sharing untyped runtime-agnostic module paths. Mandates explicit environment conditions, separated module instances, and zero cross-runtime direct imports.
globs: vite.config.{ts,js,mjs}, src/**/*.{ts,tsx,js,jsx}, server/**/*.{ts,js}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite-6-environment-api-runtime-boundary-standard"
---

# Strict Multi-Runtime Module Resolution Boundary via Vite 6 Environment API

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Cross-Runtime Symbol Contamination via Shared Module Graphs in Vite SSR Pipelines

## System Constraints
You are a Principal Software Architect enforcing Vite 6 Environment API architectural boundaries. You must prohibit mixing server-only modules (Node/Edge runtimes) into client bundle graphs. Require explicit configuration of environments (client, ssr/node, edge) in `vite.config.ts`, ensure that plugins operate within discrete environment scopes (`this.environment`), and strictly enforce boundary guardrails in code imports.

## Strict Guidelines
- Engineers MUST ALWAYS configure explicit isolated environments ('client', 'ssr', and optionally 'edge') using Vite 6 `environments` configuration rather than legacy unified SSR transforms.
- Engineers MUST NOT import server-exclusive modules (Node builtins, direct DB drivers, native bindings) into modules reachable by the 'client' environment graph.
- Vite plugins MUST inspect `this.environment.name` in hooks (`resolveId`, `load`, `transform`) before executing environment-specific logic or injecting runtime shims.
- Codebases MUST use runtime condition exports (`package.json` subpath exports with 'browser', 'edge-light', 'node') and enforce resolution conditions per Vite environment via `resolve.conditions`.
- Shared utilities MUST decouple server and client implementations using distinct file suffixes (e.g., `.server.ts`, `.client.ts`) or explicit dependency inversion to prevent transitive dependency pollution in client bundles.

## Bad vs Good Implementations
### Vite 6 Configuration: Isolated Environment Boundaries vs Shared Legacy SSR

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Legacy SSR configuration shares resolution rules across both client and server compilations. An alias or resolve setting meant for Node/Edge leaks directly into the client bundle graph, leading to bundle bloat, runtime `process` crashes, or leaked server secrets.
```typescript
import { defineConfig } from 'vite';

// ANTI-PATTERN: Unified resolution graph attempting to handle multi-runtime via ad-hoc alias
export default defineConfig({
  build: {
    ssr: true,
  },
  resolve: {
    // Leaks node builtins or edge polyfills globally across all target resolutions
    alias: {
      '@runtime-env': './src/runtime/node.ts'
    }
  }
});
```

#### Production Standard (Correct)
> **Standard**: Utilizes Vite 6's first-class Environment API to declare discrete runtime graphs. Each environment maintains its own `resolve.conditions`, output directory, and module execution context, completely preventing cross-contamination between edge, node, and browser bundles.
```typescript
import { defineConfig } from 'vite';

// PRODUCTION INVARIANT: Vite 6 Environment API defining strictly bounded runtime graphs
export default defineConfig({
  environments: {
    client: {
      build: {
        outDir: 'dist/client',
      },
      resolve: {
        conditions: ['browser', 'import', 'default'],
        noExternal: false,
      },
    },
    ssr: {
      build: {
        outDir: 'dist/server',
      },
      resolve: {
        conditions: ['node', 'import', 'default'],
        external: true,
      },
    },
    edge: {
      build: {
        outDir: 'dist/edge',
      },
      resolve: {
        conditions: ['edge-light', 'worker', 'import'],
      },
    },
  },
});
```

### Vite Plugin Implementation: Environment Isolation Scope

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Failing to check `this.environment.name` causes server transforms and confidential environment variables to be evaluated and bundled into the browser distribution.
```typescript
import type { Plugin } from 'vite';

// ANTI-PATTERN: Environment-agnostic plugin hook injecting server secrets into all builds
export function databaseContextPlugin(): Plugin {
  return {
    name: 'database-context',
    transform(code, id) {
      if (id.includes('db-provider')) {
        // Unconditionally replaces token regardless of runtime environment
        return code.replace('__DB_SECRET__', JSON.stringify(process.env.DB_PASSWORD));
      }
      return code;
    },
  };
}
```

#### Production Standard (Correct)
> **Standard**: The plugin enforces strict module boundaries using `this.environment.name`, explicitly terminating the build with `this.error` if a server-only primitive is queried in the client module graph.
```typescript
import type { Plugin } from 'vite';

// PRODUCTION INVARIANT: Strict environment qualification using Vite 6 plugin API
export function databaseContextPlugin(): Plugin {
  return {
    name: 'database-context',
    transform(code, id) {
      // Strictly prohibit running this transformation within the client environment
      if (this.environment.name === 'client') {
        if (id.includes('db-provider')) {
          this.error(`Forbidden import: 'db-provider' cannot be resolved in client environment.`);
        }
        return null;
      }

      if (this.environment.name === 'ssr' && id.includes('db-provider')) {
        return code.replace('__DB_SECRET__', JSON.stringify(process.env.DB_PASSWORD));
      }

      return null;
    },
  };
}
```
Recommended MCP Servers (mcp-serverlist.com)

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

AST Analysis Server
Analyzes AST import declarations to statically flag cross-runtime boundary leaks before bundling.
Recommended Agent Skills (askills.dev)

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

Vite Environment Verifier
CLI automation skill to validate Vite 6 environment isolation and verify client bundle purity against server symbols.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Strict Multi-Runtime Module Resolution Boundary via Vite 6 Environment API

Strict Multi-Runtime Module Resolution Boundary via Vite 6 Environment API defines an industrial-grade behavioral standard for frontend engineering. Enforces complete structural isolation between Edge, Node.js (SSR), and Client (Browser) module graphs using Vite 6's Environment API. Eliminates silent runtime symbol leaks, unintended secret exposure, and browser bundling failures caused by sharing untyped runtime-agnostic module paths. Mandates explicit environment conditions, separated module instances, and zero cross-runtime direct imports. 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 Symbol Contamination via Shared Module Graphs in Vite SSR Pipelines 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 Symbol Contamination via Shared Module Graphs in Vite SSR PipelinesCritical
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 explicit isolated environments ('client', 'ssr', and optionally 'edge') using Vite 6 `environments` configuration rather than legacy unified SSR transforms.

Engineers MUST ALWAYS configure explicit isolated environments ('client', 'ssr', and optionally 'edge') using Vite 6 `environments` configuration rather than legacy unified SSR transforms.

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 import server-exclusive modules (Node builtins, direct DB drivers, native bindings) into modules reachable by the 'client' environment graph.

Engineers MUST NOT import server-exclusive modules (Node builtins, direct DB drivers, native bindings) into modules 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.
3

Vite plugins MUST inspect `this.environment.name` in hooks (`resolveId`, `load`, `transform`) before executing environment-specific logic or injecting runtime shims.

Vite plugins MUST inspect `this.environment.name` in hooks (`resolveId`, `load`, `transform`) before executing environment-specific logic or injecting runtime shims.

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

Codebases MUST use runtime condition exports (`package.json` subpath exports with 'browser', 'edge-light', 'node') and enforce resolution conditions per Vite environment via `resolve.conditions`.

Codebases MUST use runtime condition exports (`package.json` subpath exports with 'browser', 'edge-light', 'node') and enforce resolution conditions per Vite environment via `resolve.conditions`.

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

Shared utilities MUST decouple server and client implementations using distinct file suffixes (e.g., `.server.ts`, `.client.ts`) or explicit dependency inversion to prevent transitive dependency pollution in client bundles.

Shared utilities MUST decouple server and client implementations using distinct file suffixes (e.g., `.server.ts`, `.client.ts`) or explicit dependency inversion to prevent transitive dependency pollution in 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 Strict Multi-Runtime Module Resolution Boundary via Vite 6 Environment API critical for AI coding assistants?

Enforces complete structural isolation between Edge, Node.js (SSR), and Client (Browser) module graphs using Vite 6's Environment API. Eliminates silent runtime symbol leaks, unintended secret exposure, and browser bundling failures caused by sharing untyped runtime-agnostic module paths. Mandates explicit environment conditions, separated module instances, and zero cross-runtime direct imports. 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 Symbol Contamination via Shared Module Graphs in Vite SSR Pipelines) 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

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