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frontendcritical PriorityID: vite6-environment-api-multi-runtime-isolation

Vite 6 Environment API Isolation and Multi-Runtime HMR Synchronization

Vite 6 replaces the legacy client/ssr dual-module graph with the Environment API to support isolated runtimes (Node, workerd, Edge). Developers and plugins must strictly route module transformations, module invalidations, and HMR events through scoped DevEnvironment instances and ModuleRunner transports rather than legacy root-server globals.

Prohibited Anti-Pattern: Cross-Environment Module Graph Invalidation and Unscoped HMR Dispatching via Legacy Vite 5 APIs

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---
description: Vite 6 Environment API Isolation and Multi-Runtime HMR Synchronization - Vite 6 replaces the legacy client/ssr dual-module graph with the Environment API to support isolated runtimes (Node, workerd, Edge). Developers and plugins must strictly route module transformations, module invalidations, and HMR events through scoped DevEnvironment instances and ModuleRunner transports rather than legacy root-server globals.
globs: vite.config.{ts,js,mjs}, plugins/**/*.{ts,js}, src/**/*.{ts,tsx}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite6-environment-api-multi-runtime-isolation"
---

# Vite 6 Environment API Isolation and Multi-Runtime HMR Synchronization

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Cross-Environment Module Graph Invalidation and Unscoped HMR Dispatching via Legacy Vite 5 APIs

## System Constraints
You are a Principal Software Architect enforcing Vite 6 Environment API invariants. Mandate strict environment isolation across multi-runtime execution boundaries (e.g., Node, workerd, Edge), enforce correct ModuleRunner transport layers, and prevent cross-environment pollution in plugins and HMR lifecycles.

## Strict Guidelines
- Engineers MUST ALWAYS access the module graph via `environment.moduleGraph` or `this.environment.moduleGraph`, never via deprecated `server.moduleGraph`.
- Engineers MUST NOT dispatch runtime-specific messages through `server.ws.send()`; all HMR and custom transport communication MUST use `environment.hot.send()`.
- Plugins MUST filter environment execution using `applyToEnvironment(environment: DevEnvironment)` or by inspecting `this.environment.name` within plugin hooks.
- HMR handlers MUST implement the Vite 6 `hotUpdate(options)` hook instead of deprecated `handleHotUpdate({ server, modules })` when orchestrating per-environment invalidations.
- Custom non-Node runtimes (e.g., Cloudflare workerd, browser-isolated workers) MUST communicate with the Vite dev server via an explicit `ModuleRunner` and `RunnerTransport`.

## Bad vs Good Implementations
### Vite 6 Environment-Aware Plugin vs Vite 5 Global Server State

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Accessing server.ws directly broadcasts across all runtimes indiscriminately. Calling server.ssrLoadModule ignores non-Node runtimes like workerd, and invalidating via server.moduleGraph breaks isolated environment graphs in Vite 6.
```typescript
import { Plugin } from 'vite';

export function brokenMultiRuntimePlugin(): Plugin {
  return {
    name: 'broken-multi-runtime',
    configureServer(server) {
      // VIOLATION: Using deprecated root WebSocket and global ssrLoadModule
      server.ws.on('custom:request-render', async (data) => {
        const mod = await server.ssrLoadModule('/src/entry-server.ts');
        server.ws.send({ type: 'custom', event: 'custom:rendered', data: mod.render(data) });
      });
    },
    handleHotUpdate({ server, modules }) {
      // VIOLATION: Global module graph invalidation pollutes multi-runtime setups
      for (const mod of modules) {
        server.moduleGraph.invalidateModule(mod);
      }
    }
  };
}
```

#### Production Standard (Correct)
> **Standard**: Uses Vite 6's applyToEnvironment hook to restrict execution to the intended runtime, uses the Vite 6 hotUpdate signature with environment scoping, and emits HMR notifications exclusively over environment.hot.
```typescript
import { Plugin, DevEnvironment } from 'vite';

export function vite6MultiRuntimePlugin(): Plugin {
  return {
    name: 'vite6-multi-runtime',
    // Enforce environment isolation filter
    applyToEnvironment(environment: DevEnvironment): boolean {
      return environment.name === 'ssr' || environment.name === 'workerd';
    },
    hotUpdate({ modules, environment }) {
      // Invariant: Invalidate strictly within the targeted DevEnvironment
      for (const mod of modules) {
        environment.moduleGraph.invalidateModule(mod);
      }
      // Invariant: Dispatch scoped HMR messages to the active runtime channel
      environment.hot.send({
        type: 'custom',
        event: 'runtime:module-invalidated',
        data: {
          environment: environment.name,
          modules: modules.map((m) => m.id).filter(Boolean)
        }
      });
    }
  };
}
```
Recommended MCP Servers (mcp-serverlist.com)

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

Vite Environment Inspector MCP
Inspects Vite 6 DevEnvironment state, active ModuleRunner instances, and isolated module graphs.
Recommended Agent Skills (askills.dev)

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

Vite ModuleRunner Validator
CLI utility to assert transport integrity and runtime boundaries between Vite 6 DevEnvironments.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Isolation and Multi-Runtime HMR Synchronization

Vite 6 Environment API Isolation and Multi-Runtime HMR Synchronization defines an industrial-grade behavioral standard for frontend engineering. Vite 6 replaces the legacy client/ssr dual-module graph with the Environment API to support isolated runtimes (Node, workerd, Edge). Developers and plugins must strictly route module transformations, module invalidations, and HMR events through scoped DevEnvironment instances and ModuleRunner transports rather than legacy root-server globals. 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 Graph Invalidation and Unscoped HMR Dispatching via Legacy Vite 5 APIs 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 Graph Invalidation and Unscoped HMR Dispatching via Legacy Vite 5 APIsCritical
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 access the module graph via `environment.moduleGraph` or `this.environment.moduleGraph`, never via deprecated `server.moduleGraph`.

Engineers MUST ALWAYS access the module graph via `environment.moduleGraph` or `this.environment.moduleGraph`, never via deprecated `server.moduleGraph`.

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 dispatch runtime-specific messages through `server.ws.send()`

Engineers MUST NOT dispatch runtime-specific messages through `server.ws.send()`; all HMR and custom transport communication MUST use `environment.hot.send()`.

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 filter environment execution using `applyToEnvironment(environment

Plugins MUST filter environment execution using `applyToEnvironment(environment: DevEnvironment)` or by inspecting `this.environment.name` within plugin hooks.

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

HMR handlers MUST implement the Vite 6 `hotUpdate(options)` hook instead of deprecated `handleHotUpdate({ server, modules })` when orchestrating per-environment invalidations.

HMR handlers MUST implement the Vite 6 `hotUpdate(options)` hook instead of deprecated `handleHotUpdate({ server, modules })` when orchestrating per-environment invalidations.

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

Custom non-Node runtimes (e.g., Cloudflare workerd, browser-isolated workers) MUST communicate with the Vite dev server via an explicit `ModuleRunner` and `RunnerTransport`.

Custom non-Node runtimes (e.g., Cloudflare workerd, browser-isolated workers) MUST communicate with the Vite dev server via an explicit `ModuleRunner` and `RunnerTransport`.

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 Isolation and Multi-Runtime HMR Synchronization critical for AI coding assistants?

Vite 6 replaces the legacy client/ssr dual-module graph with the Environment API to support isolated runtimes (Node, workerd, Edge). Developers and plugins must strictly route module transformations, module invalidations, and HMR events through scoped DevEnvironment instances and ModuleRunner transports rather than legacy root-server globals. 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 Graph Invalidation and Unscoped HMR Dispatching via Legacy Vite 5 APIs) 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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Vite