Vite 6 Environment API Multi-Runtime Target Sandboxing & Isolation

--- description: Vite 6 Environment API Multi-Runtime Target Sandboxing & Isolation - Enforces strict runtime boundary isolation using the Vite 6 Environment API across heterogeneous deployment targets (Node.js, Bun, workerd). Eliminates cross-runtime polyfill pollution, prevents global scope contamination, and ensures deterministic per-environment module resolution and execution pipelines. globs: vite.config.ts, vite.config.mts, src/entry-*.ts, src/server/**/*.{ts,tsx}, src/runtimes/**/*.{ts,tsx} alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/vite6-environment-api-multi-runtime-sandboxing-vite-6-environme-851" --- # Vite 6 Environment API Multi-Runtime Target Sandboxing & Isolation > **Severity**: CRITICAL | **Category**: devops > **Anti-Pattern Warning**: Monolithic SSR Configuration and Global Runtime Polyfill Leakage Across Node, Bun, and Edge Targets ## System Constraints You are a Principal DevOps and Build Infrastructure Architect enforcing strict target-specific sandboxing with the Vite 6 Environment API. Mandate discrete module graphs, runtime-specific export conditions, isolated runner instances, and zero global polyfill leaks across universal SSR applications targeting Node.js, Bun, and workerd. ## Strict Guidelines - Engineers MUST ALWAYS declare isolated runtime targets under `environments` in `vite.config.ts` using Vite 6's Environment API instead of relying on legacy top-level `ssr` configurations. - Engineers MUST configure distinct `resolve.conditions` per environment (e.g., `['workerd', 'worker']` for edge vs `['node', 'import']` for Node.js) to prevent Node built-ins from entering worker bundles. - Engineers MUST NOT inject unscoped polyfills into universal source modules or mutate `globalThis` globally; shims must be applied strictly via per-environment injected entrypoints or runner shims. - Vite plugins MUST implement environment-aware hooks (`configEnvironment`, `hotUpdate`, `transform`) checking `this.environment.name` instead of applying universal transforms across all targets. - Shared universal library code NEVER imports runtime-specific built-ins (`node:fs`, `node:async_hooks`, `Bun.serve`) without export-map separation or explicit runtime detection abstractions. ## Bad vs Good Implementations ### Vite 6 Multi-Runtime Environment Configuration #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: A single monolithic `ssr` configuration leaks conflicting export conditions (`workerd` and `node`), causing non-deterministic package resolution. Top-level `define` directives globally contaminate client and edge runtimes with Node.js primitives. ```typescript // vite.config.ts: Legacy Vite 5 monolithic SSR setup causing condition leaks and polyfill bleeding import { defineConfig } from 'vite'; export default defineConfig({ ssr: { // Pollutes resolution for both Node and workerd targets target: 'node', noExternal: true, resolve: { conditions: ['workerd', 'node', 'import'] // Ambiguous: workerd packages resolve Node fallbacks } }, define: { // Global pollution leaking into all client and edge bundles 'process.env.RUNTIME': JSON.stringify('universal'), 'global.Buffer': 'Buffer' } }); ``` #### Production Standard (Correct) > **Standard**: Defines discrete environments using the Vite 6 Environment API. Node and Edge (workerd) maintain separate resolution conditions, externalization rules, and output directories, completely eliminating cross-runtime polyfill bleed. ```typescript // vite.config.ts: Vite 6 Environment API configuration with strict runtime isolation import { defineConfig } from 'vite'; export default defineConfig({ environments: { client: { build: { outDir: 'dist/client' } }, node: { resolve: { conditions: ['node', 'import', 'module'], external: true }, build: { outDir: 'dist/node', target: 'node20' } }, edge: { resolve: { conditions: ['workerd', 'worker', 'browser'], noExternal: true // Must inline for edge runtime isolation }, build: { outDir: 'dist/edge', target: 'esnext' } } }, builder: { async buildApp(builder) { // Deterministic and isolated builds per target environment await builder.build(builder.environments.client); await builder.build(builder.environments.node); await builder.build(builder.environments.edge); } } }); ``` ### Environment-Aware Custom Vite Plugin Hook #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Applies a universal code transformation regardless of which environment is being compiled, forcing heavy Node shims into lightweight Cloudflare Worker or client-side bundles. ```typescript // plugins/runtime-inject.ts: Naive plugin polluting all environments indiscriminately import type { Plugin } from 'vite'; export function runtimeInjectPlugin(): Plugin { return { name: 'runtime-inject', transform(code, id) { // Injects Node polyfill into ALL files across client, node, and workerd return `import 'node-stdlib-browser/proxy';\n${code}`; } }; }; ``` #### Production Standard (Correct) > **Standard**: Leverages Vite 6's `configEnvironment` and inspects `this.environment.name` in hook contexts to guarantee transformations are strictly sandboxed to the target runtime. ```typescript // plugins/runtime-inject.ts: Vite 6 Environment-aware plugin lifecycle import type { Plugin } from 'vite'; export function runtimeInjectPlugin(): Plugin { return { name: 'runtime-inject', // Vite 6 hook to configure environment-specific settings configEnvironment(name, config) { if (name === 'edge') { return { resolve: { conditions: ['workerd'] } }; } }, transform(code, id) { // Strictly scope transform logic to the intended environment if (this.environment.name !== 'node') { return null; } // Only apply Node-specific instrumentation to the Node environment return code; } }; }; ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Environment API Multi-Runtime Target Sandboxing & Isolation

Vite 6 Environment API Multi-Runtime Target Sandboxing & Isolation defines an industrial-grade behavioral standard for devops engineering. Enforces strict runtime boundary isolation using the Vite 6 Environment API across heterogeneous deployment targets (Node.js, Bun, workerd). Eliminates cross-runtime polyfill pollution, prevents global scope contamination, and ensures deterministic per-environment module resolution and execution pipelines. 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: Monolithic SSR Configuration and Global Runtime Polyfill Leakage Across Node, Bun, and Edge Targets 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	Monolithic SSR Configuration and Global Runtime Polyfill Leakage Across Node, Bun, and Edge Targets	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 isolated runtime targets under `environments` in `vite.config.ts` using Vite 6's Environment API instead of relying on legacy top-level `ssr` configurations.

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.