Vite 6 Environment API Isomorphic Runtime Isolation Standard

--- description: Vite 6 Environment API Isomorphic Runtime Isolation Standard - Enforces strict memory isolation, runner boundaries, and resolve condition partitioning across Node.js, Workerd (edge), and browser environments using the Vite 6 Environment API. Prevents cross-runtime prototype pollution, illegal host-specific globals leakage, and legacy single-graph SSR execution flaws. globs: vite.config.ts, vite.config.*.ts, src/**/*.{ts,tsx}, server/**/*.{ts,tsx} alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/vite6-environment-api-runtime-isolation-vite-6-environme-259" --- # Vite 6 Environment API Isomorphic Runtime Isolation Standard > **Severity**: CRITICAL | **Category**: frontend > **Anti-Pattern Warning**: Conflating Server Execution Environments via Legacy Vite 5 SSR APIs and Leaking Node Globals into Workerd or Browser Runtimes ## System Constraints You are a Principal Software Architect enforcing the Vite 6 Environment API Isomorphic Runtime Isolation Standard. You must prevent cross-runtime contamination by strictly isolating Node.js, Workerd, and client environments during SSR dev, building, and evaluation. You reject any usage of deprecated single-runner SSR patterns, untyped environment configs, or un-scoped module evaluation. ## Strict Guidelines - Engineers MUST ALWAYS declare distinct runtime environments (e.g., `client`, `ssr`, `edge`) in `vite.config.ts` using Vite 6 `environments` definitions instead of global SSR flags. - Engineers MUST NOT call deprecated Vite SSR APIs including `server.ssrLoadModule`, `server.ssrFixStacktrace`, or `res.transformIndexHtml` in Vite 6 projects. - Plugins MUST hook into `this.environment` within plugin execution hooks (e.g., `resolveId`, `load`, `transform`) rather than relying on `options.ssr` or shared global state. - Code destined for non-Node runtimes (such as Workerd or Cloudflare Workers) MUST NOT import Node.js built-ins (`fs`, `path`, `node:crypto`) unless explicitly polyfilled or shimmed inside that environment's `resolve.conditions`. - Module runners MUST be instantiated via environment-specific instances (e.g., `server.environments.ssr.runner` or custom `ModuleRunner` with `FetchableDevEnvironmentTransport`) to preserve separate module evaluation caches. - Engineers MUST NEVER share mutable in-memory singletons across environment boundaries; all cross-environment interop MUST be achieved via strict serialization or Web standard Request/Response contracts. ## Bad vs Good Implementations ### Migrating Legacy SSR Server Loading to Vite 6 Environment ModuleRunner #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Using `server.ssrLoadModule` bypasses the Vite 6 Environment API, evaluates all modules inside the default Node host VM, and prevents execution inside targeted sandboxes like Workerd. It also leads to memory leaks and invalid condition resolution. ```typescript import { createServer } from 'vite'; const server = await createServer({ server: { middlewareMode: true }, appType: 'custom', }); // ANTI-PATTERN: Deprecated Vite 5 API, forces execution into host Node process, // ignoring isolated Workerd / edge environment constraints and shared global module caches. export async function handleRequest(url: string) { const { render } = await server.ssrLoadModule('/src/entry-server.ts'); return render(url); } ``` #### Production Standard (Correct) > **Standard**: Accessing `server.environments.ssr.runner.import` ensures that module loading honors the environment-specific resolve conditions, module graphs, and runtime transforms without cross-contaminating host and client instances. ```typescript import { createServer } from 'vite'; const server = await createServer({ server: { middlewareMode: true }, appType: 'custom', environments: { ssr: { resolve: { conditions: ['workerd', 'worker'], }, // Custom environment runner can dispatch to miniflare/workerd keepProcess: true, }, }, }); // PRODUCTION FIX: Explicitly target the dedicated environment's ModuleRunner, // ensuring resolve conditions and sandbox boundaries are strictly preserved. export async function handleRequest(url: string) { const ssrEnvironment = server.environments.ssr; const { render } = await ssrEnvironment.runner.import('/src/entry-server.ts'); return render(url); } ``` ### Environment-Aware Vite 6 Plugin Implementation #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Using `options.ssr` or `config.build.ssr` fails in multi-environment configurations where Node, browser, and edge targets execute concurrently within the same build step. ```typescript import type { Plugin } from 'vite'; // ANTI-PATTERN: Plugin inspects legacy ssr boolean flag or relies on shared module state export function brokenRuntimePlugin(): Plugin { let isSSR = false; return { name: 'broken-runtime-plugin', configResolved(config) { isSSR = Boolean(config.build.ssr); }, transform(code, id, options) { if (options?.ssr || isSSR) { return code.replace('__RUNTIME__', '"node"'); } return code.replace('__RUNTIME__', '"browser"'); }, }; } ``` #### Production Standard (Correct) > **Standard**: Using `this.environment.name` enables isolated, granular transform logic tailored to the exact environment being compiled, enforcing runtime-specific guarantees. ```typescript import type { Plugin } from 'vite'; // PRODUCTION FIX: Use `this.environment` inside plugin hooks to identify target context export function isolatedRuntimePlugin(): Plugin { return { name: 'isolated-runtime-plugin', perEnvironmentStartEndDuringDev: true, transform(code, id) { const runtimeName = this.environment.name; // 'client' | 'ssr' | 'workerd' if (this.environment.mode === 'dev' && runtimeName === 'workerd') { // Enforce Workerd specific invariants if (code.includes('process.cwd()')) { this.error(`Forbidden process.cwd() found in workerd environment: ${id}`); } } return code.replace('__RUNTIME__', JSON.stringify(runtimeName)); }, }; } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Isomorphic Runtime Isolation Standard

Vite 6 Environment API Isomorphic Runtime Isolation Standard defines an industrial-grade behavioral standard for frontend engineering. Enforces strict memory isolation, runner boundaries, and resolve condition partitioning across Node.js, Workerd (edge), and browser environments using the Vite 6 Environment API. Prevents cross-runtime prototype pollution, illegal host-specific globals leakage, and legacy single-graph SSR execution flaws. 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 Server Execution Environments via Legacy Vite 5 SSR APIs and Leaking Node Globals into Workerd or Browser Runtimes 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	Conflating Server Execution Environments via Legacy Vite 5 SSR APIs and Leaking Node Globals into Workerd or Browser Runtimes	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:

Engineers MUST ALWAYS declare distinct runtime environments (e.g., `client`, `ssr`, `edge`) in `vite.config.ts` using Vite 6 `environments` definitions instead of global 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.