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frontendcritical PriorityID: vite-6-rolldown-module-federation-chunk-isolation

Vite 6 Rolldown Module Federation Chunk Isolation & Singleton Integrity

Enforces deterministic shared runtime singletons and strict CSS/DOM chunk scoping boundaries across decoupled microfrontends compiled via Vite 6 with Rolldown. Prevents catastrophic duplicate runtime instantiation (such as dual React contexts and broken hooks) and uncontained CSS cascading collisions between host containers and dynamically loaded remotes.

Prohibited Anti-Pattern: Dual Runtime Singleton Splitting and Global Style Collision via Unbounded Rolldown Federation Bundling

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---
description: Vite 6 Rolldown Module Federation Chunk Isolation & Singleton Integrity - Enforces deterministic shared runtime singletons and strict CSS/DOM chunk scoping boundaries across decoupled microfrontends compiled via Vite 6 with Rolldown. Prevents catastrophic duplicate runtime instantiation (such as dual React contexts and broken hooks) and uncontained CSS cascading collisions between host containers and dynamically loaded remotes.
globs: vite.config.{ts,js,mjs}, src/**/*.{ts,tsx,css,scss}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/vite-6-rolldown-module-federation-chunk-isolation"
---

# Vite 6 Rolldown Module Federation Chunk Isolation & Singleton Integrity

> **Severity**: CRITICAL | **Category**: frontend
> **Anti-Pattern Warning**: Dual Runtime Singleton Splitting and Global Style Collision via Unbounded Rolldown Federation Bundling

## System Constraints
You are a Principal Software Architect enforcing enterprise-grade microfrontend boundaries for Vite 6 powered by the native Rust Rolldown bundler. You must enforce deterministic shared runtime singletons (React, ReactDOM, state management) using explicit strict-version matrices and guarantee strict CSS/DOM encapsulation preventing cross-remote global styling leaks.

## Strict Guidelines
- Engineers MUST ALWAYS configure critical framework libraries (e.g., react, react-dom, @tanstack/react-query) with 'singleton: true' and 'strictVersion: true' in the federation shared matrix to avoid dual-instantiation runtime failure.
- Engineers MUST NOT allow non-deterministic semantic version range matching ('^' or '*') across federated boundaries when compiling with Rolldown; pinning explicit semver contracts via 'requiredVersion' is mandatory.
- Code SHOULD encapsulate remote component styles using strict CSS Modules with locally scoped identity hashes or Shadow DOM encapsulation to prevent cross-chunk CSS contamination in the host.
- Services MUST ensure asynchronous federated dynamic imports provide explicit boundary fallback handling and pre-flight validation of the remote's entry manifest before chunk execution.
- Components NEVER export unscoped root-level CSS selectors (such as body, html, or broad element tags like button, div) within federated remote chunks.

## Bad vs Good Implementations
### Module Federation Configuration with Rolldown

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Declaring shared dependencies as simple strings without singleton and strictVersion constraints causes Rolldown to resolve separate instances for host and remote, throwing 'Invalid Hook Call' exceptions. It also lacks CSS chunk isolation configurations.
```typescript
import { defineConfig } from 'vite';
import { federation } from '@module-federation/vite';

export default defineConfig({
  // BAD: Missing explicit Rolldown chunking config, loose shared singletons,
  // and globally injected un-scoped styles risking collision.
  plugins: [
    federation({
      name: 'remote_app',
      filename: 'remoteEntry.js',
      exposes: {
        './Widget': './src/Widget.tsx',
      },
      shared: ['react', 'react-dom'] // Non-singleton, unversioned: causes duplicate React runtime crashes
    })
  ]
});
```

#### Production Standard (Correct)
> **Standard**: Pinning react and react-dom as singletons with strictVersion and explicit requiredVersion guarantees a unified runtime instance across boundaries. CSS Module hash namespacing prevents remote styles from bleeding into the host application.
```typescript
import { defineConfig } from 'vite';
import { federation } from '@module-federation/vite';
import packageJson from './package.json' assert { type: 'json' };

export default defineConfig({
  css: {
    modules: {
      generateScopedName: 'mf-remote-[name]__[local]___[hash:base64:5]'
    }
  },
  plugins: [
    federation({
      name: 'remote_app',
      filename: 'remoteEntry.js',
      exposes: {
        './Widget': './src/Widget.tsx'
      },
      shared: {
        react: {
          singleton: true,
          strictVersion: true,
          requiredVersion: packageJson.dependencies.react
        },
        'react-dom': {
          singleton: true,
          strictVersion: true,
          requiredVersion: packageJson.dependencies['react-dom']
        }
      }
    })
  ],
  build: {
    target: 'chrome89',
    cssCodeSplit: true,
    rolldownOptions: {
      output: {
        sanitizeFileName: true
      }
    }
  }
});
```
Recommended MCP Servers (mcp-serverlist.com)

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

Filesystem MCP
Inspects Vite configuration files, package.json dependencies, and CSS module bindings across monorepo packages.
Recommended Agent Skills (askills.dev)

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

Sherif Monorepo Linter
Validates consistent dependency versioning across federated monorepo packages to prevent singleton drift.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Vite 6 Rolldown Module Federation Chunk Isolation & Singleton Integrity

Vite 6 Rolldown Module Federation Chunk Isolation & Singleton Integrity defines an industrial-grade behavioral standard for frontend engineering. Enforces deterministic shared runtime singletons and strict CSS/DOM chunk scoping boundaries across decoupled microfrontends compiled via Vite 6 with Rolldown. Prevents catastrophic duplicate runtime instantiation (such as dual React contexts and broken hooks) and uncontained CSS cascading collisions between host containers and dynamically loaded remotes. 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: Dual Runtime Singleton Splitting and Global Style Collision via Unbounded Rolldown Federation Bundling 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 DriftDual Runtime Singleton Splitting and Global Style Collision via Unbounded Rolldown Federation BundlingCritical
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 configure critical framework libraries (e.g., react, react-dom, @tanstack/react-query) with 'singleton

Engineers MUST ALWAYS configure critical framework libraries (e.g., react, react-dom, @tanstack/react-query) with 'singleton: true' and 'strictVersion: true' in the federation shared matrix to avoid dual-instantiation runtime failure.

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 allow non-deterministic semantic version range matching ('^' or '*') across federated boundaries when compiling with Rolldown

Engineers MUST NOT allow non-deterministic semantic version range matching ('^' or '*') across federated boundaries when compiling with Rolldown; pinning explicit semver contracts via 'requiredVersion' is mandatory.

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

Code SHOULD encapsulate remote component styles using strict CSS Modules with locally scoped identity hashes or Shadow DOM encapsulation to prevent cross-chunk CSS contamination in the host.

Code SHOULD encapsulate remote component styles using strict CSS Modules with locally scoped identity hashes or Shadow DOM encapsulation to prevent cross-chunk CSS contamination in the host.

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

Services MUST ensure asynchronous federated dynamic imports provide explicit boundary fallback handling and pre-flight validation of the remote's entry manifest before chunk execution.

Services MUST ensure asynchronous federated dynamic imports provide explicit boundary fallback handling and pre-flight validation of the remote's entry manifest before chunk execution.

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

Components NEVER export unscoped root-level CSS selectors (such as body, html, or broad element tags like button, div) within federated remote chunks.

Components NEVER export unscoped root-level CSS selectors (such as body, html, or broad element tags like button, div) within federated remote chunks.

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 Rolldown Module Federation Chunk Isolation & Singleton Integrity critical for AI coding assistants?

Enforces deterministic shared runtime singletons and strict CSS/DOM chunk scoping boundaries across decoupled microfrontends compiled via Vite 6 with Rolldown. Prevents catastrophic duplicate runtime instantiation (such as dual React contexts and broken hooks) and uncontained CSS cascading collisions between host containers and dynamically loaded remotes. 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 (Dual Runtime Singleton Splitting and Global Style Collision via Unbounded Rolldown Federation Bundling) 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.

Open Specification · CC BY 4.0·Free for Personal, Team & Commercial In-Repo Use

Citation & Open Source Attribution Guidelines

This specification is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0). You are completely free to adapt and share this rule in your workspace. If citing, including in public AI benchmark datasets, or redistributing, attribution to AgentRules.org is required.

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