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frontendcritical PriorityID: vite6-environment-runtime-leakage-fence

Vite 6 Environment API Cross-Runtime Module Graph Isolation & Secret Fence

Enforces strict isolation between Vite 6 client, edge, and SSR runtime module graphs using the Environment API. Prevents server-only credentials, platform bindings, and unpolyfilled Node.js built-ins from traversing the module boundary into client-facing bundles.

Prohibited Anti-Pattern: Unfenced Module Sharing Between SSR/Edge and Client Graphs Leading to Token Exfiltration and Runtime Failures

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---
description: Vite 6 Environment API Cross-Runtime Module Graph Isolation & Secret Fence - Enforces strict isolation between Vite 6 client, edge, and SSR runtime module graphs using the Environment API. Prevents server-only credentials, platform bindings, and unpolyfilled Node.js built-ins from traversing the module boundary into client-facing bundles.
globs: vite.config.ts, vite.config.mts, src/**/*.{ts,tsx,js,jsx}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite6-environment-runtime-leakage-fence"
---

# Vite 6 Environment API Cross-Runtime Module Graph Isolation & Secret Fence

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Unfenced Module Sharing Between SSR/Edge and Client Graphs Leading to Token Exfiltration and Runtime Failures

## System Constraints
You are a Principal Architect enforcing strict runtime module graph fences using Vite 6 Environment APIs. You must prohibit direct cross-runtime imports between client, ssr, and edge execution contexts, ensuring server-only secrets and runtime-specific APIs remain strictly bounded to their designated environments.

## Strict Guidelines
- Engineers MUST configure isolated environments using the Vite 6 `environments` block (`environments.client`, `environments.ssr`, `environments.edge`) rather than relying on legacy top-level `ssr` flags.
- Engineers MUST NOT import `.server.ts` or server-scoped modules inside source files resolved under `this.environment.name === 'client'`.
- Plugins MUST inspect `this.environment.name` in hook lifecycles (`resolveId`, `load`, `transform`) before resolving virtual modules, transforming runtime globals, or injecting environment variables.
- Code destined for isomorphic consumption MUST access server secrets via explicit contract interfaces or remote procedure calls (RPC/fetch), NEVER via direct variable interpolation or server file imports.
- Services MUST enforce build-time assertions in `resolveId` to throw a fatal diagnostic error if a client-targeted module references designated server boundary files or secrets.

## Bad vs Good Implementations
### Vite 6 Environment Plugin Boundary Fence

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Using top-level define and the legacy ssr block causes global string replacement of secret variables across both client and server compilations. It lacks graph fencing, allowing the client bundle to transitively import server modules containing database credentials.
```typescript
import { defineConfig } from 'vite';

// ANTI-PATTERN: Vite 5 legacy mental model. Shared module graph allows
// client modules to accidentally resolve server files or leak process.env secrets.
export default defineConfig({
  define: {
    'process.env.DB_SECRET': JSON.stringify(process.env.DB_SECRET),
  },
  ssr: {
    noExternal: ['shared-lib'],
  },
});
```

#### Production Standard (Correct)
> **Standard**: Leverages the Vite 6 `environments` configuration block to physically decouple client and ssr graph compilation targets. Implements an environment-aware plugin hook checking `this.environment.name` to halt compilation immediately if a `.server` module leaks into the client graph.
```typescript
import { defineConfig, type Plugin } from 'vite';

// PRODUCTION INVARIANT: Vite 6 Environment API with hard module isolation fence
function environmentModuleFencePlugin(): Plugin {
  return {
    name: 'vite-environment-module-fence',
    resolveId(id, importer) {
      const env = this.environment.name;
      const isServerOnly = id.includes('.server') || id.includes('/server/');

      if (env === 'client' && isServerOnly) {
        this.error(
          `[SECURITY VIOLATION] Cross-runtime leakage detected: Client environment module '${importer}' cannot import server-only module '${id}'.`
        );
      }
      return null;
    },
  };
}

export default defineConfig({
  plugins: [environmentModuleFencePlugin()],
  environments: {
    client: {
      build: {
        outDir: 'dist/client',
        rollupOptions: {
          input: '/src/entry-client.tsx',
        },
      },
      define: {
        __RUNTIME_ENV__: JSON.stringify('client'),
      },
    },
    ssr: {
      build: {
        outDir: 'dist/server',
        rollupOptions: {
          input: '/src/entry-server.tsx',
        },
      },
      define: {
        __RUNTIME_ENV__: JSON.stringify('ssr'),
      },
    },
  },
});
```
Recommended MCP Servers (mcp-serverlist.com)

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

AST Dependency Analyzer MCP
Scans import graphs and traces dependency chains to identify cross-boundary leaks between server-side files and client entries.
Recommended Agent Skills (askills.dev)

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

Secretlint Static Scanner
Scans bundle artifacts and client distribution directories for leaked environment secrets, private keys, and credential strings.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Cross-Runtime Module Graph Isolation & Secret Fence

Vite 6 Environment API Cross-Runtime Module Graph Isolation & Secret Fence defines an industrial-grade behavioral standard for frontend engineering. Enforces strict isolation between Vite 6 client, edge, and SSR runtime module graphs using the Environment API. Prevents server-only credentials, platform bindings, and unpolyfilled Node.js built-ins from traversing the module boundary into client-facing 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: Unfenced Module Sharing Between SSR/Edge and Client Graphs Leading to Token Exfiltration and Runtime Failures 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 DriftUnfenced Module Sharing Between SSR/Edge and Client Graphs Leading to Token Exfiltration and Runtime FailuresCritical
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 configure isolated environments using the Vite 6 `environments` block (`environments.client`, `environments.ssr`, `environments.edge`) rather than relying on legacy top-level `ssr` flags.

Engineers MUST configure isolated environments using the Vite 6 `environments` block (`environments.client`, `environments.ssr`, `environments.edge`) rather than relying on legacy top-level `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 import `.server.ts` or server-scoped modules inside source files resolved under `this.environment.name === 'client'`.

Engineers MUST NOT import `.server.ts` or server-scoped modules inside source files resolved under `this.environment.name === 'client'`.

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 inspect `this.environment.name` in hook lifecycles (`resolveId`, `load`, `transform`) before resolving virtual modules, transforming runtime globals, or injecting environment variables.

Plugins MUST inspect `this.environment.name` in hook lifecycles (`resolveId`, `load`, `transform`) before resolving virtual modules, transforming runtime globals, or injecting environment variables.

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 destined for isomorphic consumption MUST access server secrets via explicit contract interfaces or remote procedure calls (RPC/fetch), NEVER via direct variable interpolation or server file imports.

Code destined for isomorphic consumption MUST access server secrets via explicit contract interfaces or remote procedure calls (RPC/fetch), NEVER via direct variable interpolation or server file imports.

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 MUST enforce build-time assertions in `resolveId` to throw a fatal diagnostic error if a client-targeted module references designated server boundary files or secrets.

Services MUST enforce build-time assertions in `resolveId` to throw a fatal diagnostic error if a client-targeted module references designated server boundary files or secrets.

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 Module Graph Isolation & Secret Fence critical for AI coding assistants?

Enforces strict isolation between Vite 6 client, edge, and SSR runtime module graphs using the Environment API. Prevents server-only credentials, platform bindings, and unpolyfilled Node.js built-ins from traversing the module boundary into client-facing 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 (Unfenced Module Sharing Between SSR/Edge and Client Graphs Leading to Token Exfiltration and Runtime Failures) 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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