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frontendcritical PriorityID: vite-6-environment-api-multi-runtime-isolation-standard-vite-6-environme-128

Vite 6 Environment API Multi-Runtime Context Isolation Standard

Enforces strict memory, configuration, and module-graph boundary separation between heterogeneous target runtimes (e.g., Cloudflare Workers/workerd and Node.js) using the Vite 6 Environment API. Prevents runtime pollution, invalid cross-runtime polyfill leakage, and module graph cache poisoning during dual-target SSR builds. Mandates explicit environment-scoped resolve conditions, isolated runner instances, and contextual plugin execution.

Prohibited Anti-Pattern: Cross-Runtime Module Graph Contamination via Shared Vite SSR State and Global Conditions

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---
description: Vite 6 Environment API Multi-Runtime Context Isolation Standard - Enforces strict memory, configuration, and module-graph boundary separation between heterogeneous target runtimes (e.g., Cloudflare Workers/workerd and Node.js) using the Vite 6 Environment API. Prevents runtime pollution, invalid cross-runtime polyfill leakage, and module graph cache poisoning during dual-target SSR builds. Mandates explicit environment-scoped resolve conditions, isolated runner instances, and contextual plugin execution.
globs: vite.config.{ts,js,mjs,cjs}, 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-multi-runtime-isolation-standard-vite-6-environme-128"
---

# Vite 6 Environment API Multi-Runtime Context Isolation Standard

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Cross-Runtime Module Graph Contamination via Shared Vite SSR State and Global Conditions

## System Constraints
You are a Principal Software Architect enforcing the Vite 6 Environment API SSR Multi-Runtime Context Isolation Standard. Vite 6 deprecates monolithic SSR options in favor of granular environments (e.g., client, ssr, edge/workerd). You must ensure that developers never share module graphs, resolve conditions, or runtime runners between heterogeneous environments like Node.js and Cloudflare Workers. Reject any code that attempts to resolve Node-specific built-ins in edge environments, leaks shared module states across environments, or relies on legacy, un-scoped plugin hooks without environment discrimination.

## Strict Guidelines
- Engineers MUST ALWAYS declare distinct runtime targets using the top-level `environments` configuration block in `vite.config.ts` (e.g., separate `client`, `ssr` for Node, and `workerd` for Cloudflare Workers).
- Engineers MUST NOT use legacy monolithic `ssr.target` or shared `resolve.conditions` when compiling for dual-runtime SSR architectures.
- Vite plugins MUST ALWAYS query `this.environment.name` or `this.environment.mode` within hooks (`resolveId`, `load`, `transform`) before applying runtime-specific transforms.
- Engineers MUST configure hermetic `resolve.conditions` and `resolve.externalConditions` uniquely per environment to prevent Node.js built-ins from being resolved into worker/edge bundles.
- Server entrypoints and dev orchestrators MUST instantiate separate `ModuleRunner` instances for each runtime environment rather than invoking `ssrLoadModule` globally on a shared Vite dev server.
- Engineers MUST isolate shared memory singletons across environment boundaries by avoiding module-level mutable variables that bridge server and client execution contexts.
- Build scripts MUST execute dual-target builds via `builder.build(builder.environments[name])` to ensure deterministic, isolated rollup phases per target runtime.

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

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Configuring global resolve conditions and legacy ssr properties creates cross-runtime module graph poisoning. It causes Node-specific dependencies to attempt worker imports and forces webworker conditions onto the client bundle, crashing builds and leaking Node globals into edge workers.
```typescript
import { defineConfig } from 'vite';

// Anti-pattern: Monolithic SSR configuration sharing conditions across heterogeneous targets
export default defineConfig({
  ssr: {
    target: 'webworker',
    noExternal: true,
  },
  resolve: {
    // Leaks worker conditions into Node tools and client graph
    conditions: ['workerd', 'worker', 'browser'],
  },
  build: {
    outDir: 'dist',
  },
});
```

#### Production Standard (Correct)
> **Standard**: Explicitly declares dedicated environments ('client', 'node', and 'edge') with discrete resolve and external conditions, ensuring the Vite 6 module graph and bundling pipeline remain isolated across runtimes.
```typescript
import { defineConfig } from 'vite';

// Production invariant: Explicit Vite 6 Environment API with isolated runtime configurations
export default defineConfig({
  environments: {
    client: {
      resolve: {
        conditions: ['browser'],
      },
      build: {
        outDir: 'dist/client',
      },
    },
    node: {
      resolve: {
        conditions: ['node'],
        externalConditions: ['node'],
      },
      build: {
        outDir: 'dist/server/node',
        ssr: true,
      },
    },
    edge: {
      resolve: {
        conditions: ['workerd', 'worker', 'browser'],
        externalConditions: ['workerd', 'worker'],
      },
      build: {
        outDir: 'dist/server/edge',
        ssr: true,
      },
    },
  },
});
```

### Environment-Aware Vite Plugin Hook Discrimination

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Checking only `options.ssr` fails in multi-runtime architectures because it treats Cloudflare Workers (workerd) and Node.js identically, serving Node-specific modules to edge runtimes.
```typescript
import type { Plugin } from 'vite';

export function runtimeGuardPlugin(): Plugin {
  return {
    name: 'runtime-guard',
    resolveId(id, importer, options) {
      // Anti-pattern: Using only legacy boolean flag options.ssr without checking target environment
      if (options?.ssr && id === 'virtual:runtime-config') {
        return '\0virtual:runtime-config-node';
      }
      return null;
    },
  };
}
```

#### Production Standard (Correct)
> **Standard**: Leverages `this.environment.name` provided by Vite 6 plugin contexts to return the appropriate runtime implementation without cross-contaminating module graphs.
```typescript
import type { Plugin } from 'vite';

export function runtimeGuardPlugin(): Plugin {
  return {
    name: 'runtime-guard',
    resolveId(id, importer) {
      if (id !== 'virtual:runtime-config') return null;

      // Production invariant: Inspect this.environment to resolve runtime-safe virtual modules
      const envName = this.environment.name;
      if (envName === 'edge') {
        return '\0virtual:runtime-config-edge';
      }
      if (envName === 'node') {
        return '\0virtual:runtime-config-node';
      }
      return '\0virtual:runtime-config-client';
    },
  };
}
```
Recommended MCP Servers (mcp-serverlist.com)

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

Cloudflare Workers MCP Server
Validates edge-runtime constraints, bindings, and workerd compatibility flags in multi-runtime SSR builds.
Recommended Agent Skills (askills.dev)

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

Vite Ecosystem CI Validator
CLI automation skill to test multi-environment configurations and SSR module isolation across heterogeneous runtimes.
Architectural Specification & Invariant Rationale

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

Vite 6 Environment API Multi-Runtime Context Isolation Standard defines an industrial-grade behavioral standard for frontend engineering. Enforces strict memory, configuration, and module-graph boundary separation between heterogeneous target runtimes (e.g., Cloudflare Workers/workerd and Node.js) using the Vite 6 Environment API. Prevents runtime pollution, invalid cross-runtime polyfill leakage, and module graph cache poisoning during dual-target SSR builds. Mandates explicit environment-scoped resolve conditions, isolated runner instances, and contextual plugin execution. 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 Module Graph Contamination via Shared Vite SSR State and Global Conditions 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 Module Graph Contamination via Shared Vite SSR State and Global ConditionsCritical
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 declare distinct runtime targets using the top-level `environments` configuration block in `vite.config.ts` (e.g., separate `client`, `ssr` for Node, and `workerd` for Cloudflare Workers).

Engineers MUST ALWAYS declare distinct runtime targets using the top-level `environments` configuration block in `vite.config.ts` (e.g., separate `client`, `ssr` for Node, and `workerd` for Cloudflare Workers).

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 legacy monolithic `ssr.target` or shared `resolve.conditions` when compiling for dual-runtime SSR architectures.

Engineers MUST NOT use legacy monolithic `ssr.target` or shared `resolve.conditions` when compiling for dual-runtime SSR architectures.

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 ALWAYS query `this.environment.name` or `this.environment.mode` within hooks (`resolveId`, `load`, `transform`) before applying runtime-specific transforms.

Vite plugins MUST ALWAYS query `this.environment.name` or `this.environment.mode` within hooks (`resolveId`, `load`, `transform`) before applying runtime-specific 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.
4

Engineers MUST configure hermetic `resolve.conditions` and `resolve.externalConditions` uniquely per environment to prevent Node.js built-ins from being resolved into worker/edge bundles.

Engineers MUST configure hermetic `resolve.conditions` and `resolve.externalConditions` uniquely per environment to prevent Node.js built-ins from being resolved into worker/edge 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.
5

Server entrypoints and dev orchestrators MUST instantiate separate `ModuleRunner` instances for each runtime environment rather than invoking `ssrLoadModule` globally on a shared Vite dev server.

Server entrypoints and dev orchestrators MUST instantiate separate `ModuleRunner` instances for each runtime environment rather than invoking `ssrLoadModule` globally on a shared Vite dev server.

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

Engineers MUST isolate shared memory singletons across environment boundaries by avoiding module-level mutable variables that bridge server and client execution contexts.

Engineers MUST isolate shared memory singletons across environment boundaries by avoiding module-level mutable variables that bridge server and client execution contexts.

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.
7

Build scripts MUST execute dual-target builds via `builder.build(builder.environments[name])` to ensure deterministic, isolated rollup phases per target runtime.

Build scripts MUST execute dual-target builds via `builder.build(builder.environments[name])` to ensure deterministic, isolated rollup phases per target runtime.

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 Isolation Standard critical for AI coding assistants?

Enforces strict memory, configuration, and module-graph boundary separation between heterogeneous target runtimes (e.g., Cloudflare Workers/workerd and Node.js) using the Vite 6 Environment API. Prevents runtime pollution, invalid cross-runtime polyfill leakage, and module graph cache poisoning during dual-target SSR builds. Mandates explicit environment-scoped resolve conditions, isolated runner instances, and contextual plugin execution. 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 Module Graph Contamination via Shared Vite SSR State and Global Conditions) 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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