Vite 6 Environment API Deterministic Multi-Runtime Isolation Standard

--- description: Vite 6 Environment API Deterministic Multi-Runtime Isolation Standard - Enforces deterministic module graph segregation and runtime boundaries across heterogeneous environments (Workerd, Node, Browser) using Vite 6 Environment APIs. Prevents dual-package hazards, runtime context leaks, and accidental bundle pollution caused by legacy SSR flags or unified module resolution paths. globs: vite.config.{ts,js,mjs}, 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 Environment API Deterministic Multi-Runtime Isolation Standard > **Severity**: CRITICAL | **Category**: frontend > **Anti-Pattern Warning**: Unified Module Resolution Bleeding Server Secrets or Dual-Package Singletons across Heterogeneous Runtimes ## System Constraints You are a Principal Software Architect enforcing the Vite 6 Environment API Multi-Runtime Isolation Standard. You must mandate strict module graph segregation between heterogeneous runtimes (such as client, node, and workerd/edge). Forbid legacy Vite SSR patterns (e.g., relying purely on `ssrLoadModule` without explicit environment targeting or sharing un-isolated plugin states across environments). Ensure module resolution conditions, build output targets, and externalized dependencies are scoped per-environment to prevent state corruption, dual-package hazards, and secret leakage into the client bundle. ## Strict Guidelines - Engineers MUST ALWAYS configure distinct environments using `environments.<name>` in `vite.config.ts` instead of relying on legacy monolithic `ssr` configuration blocks. - Engineers MUST specify explicit `resolve.conditions` and `resolve.externalConditions` for each discrete environment (e.g., ['workerd', 'worker'] vs ['node'] vs ['browser']). - Engineers MUST NOT share stateful plugin hook caches or singletons across multiple Vite 6 environments without explicit namespace scoping via `this.environment.name`. - Custom dev server runners MUST dispatch module execution through `server.environments[name]` and the Environment API instead of deprecated `server.ssrLoadModule`. - Code executing in edge/workerd environments MUST NOT import Node.js built-ins unless explicitly polyfilled or provided by the targeted environment runner. - Client bundles MUST NOT import modules containing runtime secrets or server-only execution pathways; enforcement MUST occur via per-environment alias and resolve restrictions. ## Bad vs Good Implementations ### Configuring Multi-Runtime Isolation with Vite 6 Environment API #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Applying global resolve conditions like 'workerd' to the root config leaks edge conditions into the client bundle, causing dual-package hazards and runtime execution mismatches. ```typescript import { defineConfig } from 'vite'; // ANTI-PATTERN: Monolithic configuration mixing edge worker and browser resolution export default defineConfig({ ssr: { target: 'webworker', noExternal: true, }, resolve: { // Leaks workerd export condition into client/node resolution conditions: ['workerd', 'import'], }, build: { ssr: 'src/entry-server.ts', }, }); ``` #### Production Standard (Correct) > **Standard**: Defining separate 'client' and 'ssr' environments within the `environments` block ensures independent module graphs, distinct resolution conditions, and isolated build outputs. ```typescript import { defineConfig } from 'vite'; // PRODUCTION INVARIANT: Explicit environment segregation export default defineConfig({ environments: { client: { build: { outDir: 'dist/client', }, resolve: { conditions: ['browser'], }, }, ssr: { build: { outDir: 'dist/edge', }, resolve: { conditions: ['workerd', 'worker'], externalConditions: ['workerd'], }, }, }, builder: { buildApp: async (builder) => { await builder.build(builder.environments.client); await builder.build(builder.environments.ssr); }, }, }); ``` ### Per-Environment Plugin Isolation and Dev Execution #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The plugin shares a raw module cache across both client and SSR pipelines without accounting for environment identity, leading to cache poisoning. Additionally, `server.ssrLoadModule` bypasses Environment API runner boundaries. ```typescript import type { Plugin, ViteDevServer } from 'vite'; // ANTI-PATTERN: Global cache leaking across environments and legacy execution export function leakyPlugin(): Plugin { const transformCache = new Map<string, string>(); return { name: 'leaky-cache-plugin', transform(code, id) { if (transformCache.has(id)) return transformCache.get(id); transformCache.set(id, code); return code; }, configureServer(server: ViteDevServer) { server.middlewares.use(async (req, res) => { // Deprecated monolithic runner mixing module graphs const mod = await server.ssrLoadModule('/src/entry-server.ts'); mod.render(req, res); }); }, }; } ``` #### Production Standard (Correct) > **Standard**: Accessing `this.environment.name` ensures plugin-level caches are segregated per runtime graph, and `server.environments.ssr.runner.import` guarantees execution occurs strictly within the designated environment's runner context. ```typescript import type { Plugin, ViteDevServer } from 'vite'; // PRODUCTION INVARIANT: Environment-aware hook scoping and runner dispatch export function isolatedPlugin(): Plugin { const envCaches = new Map<string, Map<string, string>>(); return { name: 'isolated-cache-plugin', transform(code, id) { const envName = this.environment.name; if (!envCaches.has(envName)) { envCaches.set(envName, new Map()); } const cache = envCaches.get(envName)!; if (cache.has(id)) return cache.get(id); cache.set(id, code); return code; }, configureServer(server: ViteDevServer) { server.middlewares.use(async (req, res, next) => { const ssrEnv = server.environments.ssr; if (!ssrEnv) return next(); const runner = ssrEnv.runner; const mod = await runner.import('/src/entry-server.ts'); mod.render(req, res); }); }, }; } ```

Architectural Specification & Invariant Rationale

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

Vite 6 Environment API Deterministic Multi-Runtime Isolation Standard defines an industrial-grade behavioral standard for frontend engineering. Enforces deterministic module graph segregation and runtime boundaries across heterogeneous environments (Workerd, Node, Browser) using Vite 6 Environment APIs. Prevents dual-package hazards, runtime context leaks, and accidental bundle pollution caused by legacy SSR flags or unified module resolution paths. 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: Unified Module Resolution Bleeding Server Secrets or Dual-Package Singletons across Heterogeneous 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	Unified Module Resolution Bleeding Server Secrets or Dual-Package Singletons across Heterogeneous 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 configure distinct environments using `environments.<name>` in `vite.config.ts` instead of relying on legacy monolithic `ssr` configuration blocks.

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.