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

Vite 6 Environment API Multi-Runtime Context Boundary Invariant

Enforces strict physical isolation across execution environments (client, Node.js SSR, and edge runtimes) within the Vite 6 Environment API. Prevents cross-runtime module graph pollution, leaked global polyfills, and improper shared plugin state across disparate target runtimes during isomorphic build and dev evaluation.

Prohibited Anti-Pattern: Conflating Module Resolution Contexts and Leaking Node Polyfills into Edge Runtimes via Legacy SSR Flags

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---
description: Vite 6 Environment API Multi-Runtime Context Boundary Invariant - Enforces strict physical isolation across execution environments (client, Node.js SSR, and edge runtimes) within the Vite 6 Environment API. Prevents cross-runtime module graph pollution, leaked global polyfills, and improper shared plugin state across disparate target runtimes during isomorphic build and dev evaluation.
globs: vite.config.{ts,js,mjs,mts}, plugins/**/*.{ts,js,mts}, 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-runtime-boundary-invariant"
---

# Vite 6 Environment API Multi-Runtime Context Boundary Invariant

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Conflating Module Resolution Contexts and Leaking Node Polyfills into Edge Runtimes via Legacy SSR Flags

## System Constraints
You are a Principal Software Architect enforcing runtime isolation in Vite 6 multi-environment configurations. You must mandate strict separation between client, node, and edge environment graphs using Vite 6's Environment API (`builder.buildApp`, `this.environment`, `createBuilder`). Prevent cross-environment pollution, shared mutable plugin caches, and leaking Node/DOM polyfills into incompatible runtime contexts.

## Strict Guidelines
- Engineers MUST ALWAYS inspect `this.environment.name` or `this.environment.mode` within Vite plugin hooks (`resolveId`, `load`, `transform`) rather than relying on legacy `options.ssr` flags.
- Engineers MUST NOT share in-memory singleton caches, polyfill registrations, or module transformation states across different environments inside custom Vite plugins.
- Vite configurations MUST define explicit `resolve.conditions` per runtime environment (e.g., `['worker', 'workerd']` for edge vs `['node']` for SSR) to guarantee separate condition matching.
- Code targeted for edge environments MUST NEVER import or inject Node.js runtime built-ins (`fs`, `node:path`, `node:buffer`) unless wrapped by an isolated environment polyfill explicitly mapped to that environment's graph.
- Isomorphic code executing under `ModuleRunner` MUST NOT mutate global objects (`globalThis`, `window`, `process`) without scoped teardown to prevent contamination across parallel environment runners.

## Bad vs Good Implementations
### Vite 6 Multi-Environment Plugin and Runtime Boundary Configuration

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: The legacy `options.ssr` flag collapses all non-browser environments into a single bucket, causing Node.js built-ins (`node:buffer`) to bleed into edge runtimes (e.g., Cloudflare Workers). The shared moduleCache introduces cross-environment graph contamination across concurrent builds.
```typescript
import { defineConfig } from 'vite';

// ANTI-PATTERN: Leaky module cache shared globally across environments
const moduleCache = new Map<string, string>();

export default defineConfig({
  // Legacy SSR configuration conflating edge and node execution targets
  build: {
    ssr: true,
  },
  plugins: [
    {
      name: 'leaky-runtime-plugin',
      transform(code, id, options) {
        // Relies on legacy boolean; ignores whether target is edge (workerd) or Node.js
        if (options?.ssr) {
          // Injects node global unconditionally, contaminating edge/worker runtimes
          return `import Buffer from 'node:buffer';\n${code}`;
        }
        if (moduleCache.has(id)) {
          return moduleCache.get(id);
        }
        moduleCache.set(id, code);
        return code;
      },
    },
  ],
});
```

#### Production Standard (Correct)
> **Standard**: Uses Vite 6 Environment API with explicitly decoupled `client`, `ssr` (Node), and `edge` configurations. Plugin logic evaluates `this.environment.name` ensuring module transformations and imports remain fenced to their corresponding target runtime.
```typescript
import { defineConfig } from 'vite';

export default defineConfig({
  environments: {
    client: {
      build: {
        outDir: 'dist/client',
      },
    },
    ssr: {
      resolve: {
        conditions: ['node'],
        externalConditions: ['node'],
      },
      build: {
        outDir: 'dist/ssr',
      },
    },
    edge: {
      resolve: {
        conditions: ['workerd', 'worker'],
        noExternal: true,
      },
      build: {
        outDir: 'dist/edge',
      },
    },
  },
  plugins: [
    {
      name: 'isolated-runtime-plugin',
      // Vite 6 per-environment transform lifecycle hook
      transform(code, id) {
        const envName = this.environment.name;

        // Invariant: enforce strict runtime boundaries by environment name
        if (envName === 'ssr') {
          return `import process from 'node:process';\n${code}`;
        }

        if (envName === 'edge') {
          // Invariant: Node built-ins strictly prohibited in edge context
          if (code.includes('node:process') || code.includes('node:buffer')) {
            this.error(`Node built-in violation in edge environment for module: ${id}`);
          }
        }

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

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

Vite AST Inspector MCP
Static analysis MCP server to validate Vite configuration and AST graph boundaries across multi-environment builds.
Recommended Agent Skills (askills.dev)

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

Vite 6 Environment Configuration Auditor
CLI skill that audits Vite configurations to verify that resolve conditions and plugin hooks comply with Vite 6 multi-runtime fencing invariants.
Architectural Specification & Invariant Rationale

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

Vite 6 Environment API Multi-Runtime Context Boundary Invariant defines an industrial-grade behavioral standard for frontend engineering. Enforces strict physical isolation across execution environments (client, Node.js SSR, and edge runtimes) within the Vite 6 Environment API. Prevents cross-runtime module graph pollution, leaked global polyfills, and improper shared plugin state across disparate target runtimes during isomorphic build and dev evaluation. 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: Conflating Module Resolution Contexts and Leaking Node Polyfills into Edge Runtimes via Legacy SSR Flags 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 DriftConflating Module Resolution Contexts and Leaking Node Polyfills into Edge Runtimes via Legacy SSR FlagsCritical
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 inspect `this.environment.name` or `this.environment.mode` within Vite plugin hooks (`resolveId`, `load`, `transform`) rather than relying on legacy `options.ssr` flags.

Engineers MUST ALWAYS inspect `this.environment.name` or `this.environment.mode` within Vite plugin hooks (`resolveId`, `load`, `transform`) rather than relying on legacy `options.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 share in-memory singleton caches, polyfill registrations, or module transformation states across different environments inside custom Vite plugins.

Engineers MUST NOT share in-memory singleton caches, polyfill registrations, or module transformation states across different environments inside custom Vite plugins.

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 configurations MUST define explicit `resolve.conditions` per runtime environment (e.g., `['worker', 'workerd']` for edge vs `['node']` for SSR) to guarantee separate condition matching.

Vite configurations MUST define explicit `resolve.conditions` per runtime environment (e.g., `['worker', 'workerd']` for edge vs `['node']` for SSR) to guarantee separate condition matching.

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 targeted for edge environments MUST NEVER import or inject Node.js runtime built-ins (`fs`, `node

Code targeted for edge environments MUST NEVER import or inject Node.js runtime built-ins (`fs`, `node:path`, `node:buffer`) unless wrapped by an isolated environment polyfill explicitly mapped to that environment's 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

Isomorphic code executing under `ModuleRunner` MUST NOT mutate global objects (`globalThis`, `window`, `process`) without scoped teardown to prevent contamination across parallel environment runners.

Isomorphic code executing under `ModuleRunner` MUST NOT mutate global objects (`globalThis`, `window`, `process`) without scoped teardown to prevent contamination across parallel environment runners.

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 Context Boundary Invariant critical for AI coding assistants?

Enforces strict physical isolation across execution environments (client, Node.js SSR, and edge runtimes) within the Vite 6 Environment API. Prevents cross-runtime module graph pollution, leaked global polyfills, and improper shared plugin state across disparate target runtimes during isomorphic build and dev evaluation. 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 (Conflating Module Resolution Contexts and Leaking Node Polyfills into Edge Runtimes via Legacy SSR Flags) 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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