Vite 6 Environment API & Multi-Runtimes Architecture Standard

Vite 6 deprecates monolithic SSR transforms in favor of the Environment API, isolating module graphs and module runners across distinct runtimes (Node.js, Edge, workerd, and Client). Conflating environment module graphs or invoking deprecated APIs like `ssrLoadModule` causes cross-runtime state leakage, broken HMR transport boundaries, and unhandled execution crashes. Strict boundary isolation across `server.environments` MUST be enforced to guarantee deterministic compilation and Hot Module Replacement.

--- description: Vite 6 Environment API & Multi-Runtimes Architecture Standard - Vite 6 deprecates monolithic SSR transforms in favor of the Environment API, isolating module graphs and module runners across distinct runtimes (Node.js, Edge, workerd, and Client). Conflating environment module graphs or invoking deprecated APIs like `ssrLoadModule` causes cross-runtime state leakage, broken HMR transport boundaries, and unhandled execution crashes. Strict boundary isolation across `server.environments` MUST be enforced to guarantee deterministic compilation and Hot Module Replacement. globs: vite.config.*, **/server/**/*.{ts,js,mjs}, **/src/**/*.{ts,js,tsx,jsx} alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/vite-6-environment-api-multi-runtimes-production-standard" --- # Vite 6 Environment API & Multi-Runtimes Architecture Standard > **Severity**: CRITICAL | **Category**: frontend > **Anti-Pattern Warning**: Defaulting to legacy `ssrLoadModule` and accessing shared server transform caches across multi-runtime targets instead of scoped `DevEnvironment` instances. ## System Constraints You are an expert Vite 6 systems architect specializing in runtime isolation and the Vite Environment API. You MUST ensure that multi-runtime execution boundaries (Client, SSR, Edge/workerd) are maintained through independent `DevEnvironment` definitions and `ModuleRunner` abstractions. You MUST reject all legacy Vite 5 SSR APIs (`ssrLoadModule`, `ssrTransform`, `ssrFixStacktrace`) and enforce rigorous HMR channel scoping. ## Strict Guidelines - Developers MUST NOT use legacy Vite SSR APIs (`server.ssrLoadModule`, `server.ssrTransform`, `server.ssrFixStacktrace`) and MUST migrate to `server.environments[name]` and the decoupled `ModuleRunner` API. - Custom runtimes (such as Cloudflare workerd or V8 Isolates) MUST implement a dedicated `DevEnvironment` with configured `transport` and `runner` instances to prevent Node.js built-ins from leaking into isolated environments. - Custom plugins injecting runtime hooks MUST check `this.environment.name` instead of relying on legacy `options.ssr` boolean flags. - HMR event listeners and hot updates MUST ALWAYS be scoped to their targeted environment via `environment.hot.send` to prevent broadcast contamination across unrelated runtimes. - Plugins that modify module graphs MUST interact solely with `this.environment.moduleGraph` to preserve discrete resolution caches per target runtime. ## Bad vs Good Implementations ### Migrating from Legacy ssrLoadModule to Vite 6 Environment API and ModuleRunner #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Vite 6 obsoletes `server.ssrLoadModule` and `server.ssrFixStacktrace`. Using them bypasses the Vite 6 Environment API, forcing all server executions through the legacy Node.js SSR pipeline, breaking custom runtime semantics (e.g., workerd/edge), and causing memory leaks across distinct module graphs. ```typescript import type { ViteDevServer } from 'vite'; export async function handleDevRequest( server: ViteDevServer, url: string, runtimeTarget: 'ssr' | 'edge' ): Promise<unknown> { // Anti-pattern: Using legacy ssrLoadModule across runtimes. // This ignores Vite 6 independent environment isolation and leaks Node context. try { const entryModule = await server.ssrLoadModule(url); return entryModule; } catch (error) { server.ssrFixStacktrace(error as Error); throw error; } } ``` #### Production Standard (Correct) > **Standard**: This approach targets the discrete `DevEnvironment` registered in `server.environments[name]`, creates an isolated `ModuleRunner`, passes execution through the explicit transport channel, and avoids cross-runtime module graph pollution. ```typescript import { createServer, type ViteDevServer } from 'vite'; import { ModuleRunner, ESModulesRunner } from 'vite/module-runner'; export async function loadEnvironmentEntry( server: ViteDevServer, environmentName: string, entryUrl: string ): Promise<Record<string, unknown>> { const environment = server.environments[environmentName]; if (!environment) { throw new Error(`[vite] Environment "${environmentName}" is not registered on the dev server.`); } // Use isolated ModuleRunner bound to the target environment's transport const runner = new ModuleRunner( { root: server.config.root, transport: { invoke: async (payload) => { return await environment.hot.handleInvoke(payload); } } }, new ESModulesRunner() ); try { const mod = await runner.import(entryUrl); return mod as Record<string, unknown>; } catch (error) { if (error instanceof Error) { // Fix stack traces directly through the targeted environment environment.hot.send({ type: 'error', err: { message: error.message, stack: error.stack ?? '' } }); } throw error; } finally { await runner.close(); } } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API & Multi-Runtimes Architecture Standard

Vite 6 Environment API & Multi-Runtimes Architecture Standard defines an industrial-grade behavioral standard for frontend engineering. Vite 6 deprecates monolithic SSR transforms in favor of the Environment API, isolating module graphs and module runners across distinct runtimes (Node.js, Edge, workerd, and Client). Conflating environment module graphs or invoking deprecated APIs like `ssrLoadModule` causes cross-runtime state leakage, broken HMR transport boundaries, and unhandled execution crashes. Strict boundary isolation across `server.environments` MUST be enforced to guarantee deterministic compilation and Hot Module Replacement. 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: Defaulting to legacy `ssrLoadModule` and accessing shared server transform caches across multi-runtime targets instead of scoped `DevEnvironment` instances. 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 Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Defaulting to legacy `ssrLoadModule` and accessing shared server transform caches across multi-runtime targets instead of scoped `DevEnvironment` instances.	Critical	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 Inconsistency	AI 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:

Developers MUST NOT use legacy Vite SSR APIs (`server.ssrLoadModule`, `server.ssrTransform`, `server.ssrFixStacktrace`) and MUST migrate to `server.environments[name]` and the decoupled `ModuleRunner` API.

Developers MUST NOT use legacy Vite SSR APIs (`server.ssrLoadModule`, `server.ssrTransform`, `server.ssrFixStacktrace`) and MUST migrate to `server.environments[name]` and the decoupled `ModuleRunner` API.

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.