Add a skill for rushstack (#5613)

* feat: add rushstack skill

* feat: add a skill for RushStack

* feat: add a skill for RushStack

* feat: add a skill for RushStack

* feat: add CHANGELOG.md

Author: L-Qun

skills/rushstack-best-practices/CHANGELOG.md

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+# Change Log - Rush Stack Skills
+
+This log was last generated on Tue, 11 Feb 2026 00:00:00 GMT and should not be manually modified.
+
+## 1.0.0
+Tue, 11 Feb 2026 00:00:00 GMT
+
+### Minor changes
+
+- Initial release of Rush Stack skills collection
+- `rushstack-best-practices` skill providing guidance for:
+  - Configuring Rush in a monorepo
+  - Common configuration patterns
+  - Package management best practices
+  - Build and toolchain recommendations
+

skills/rushstack-best-practices/SKILL.md

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+---
+name: rushstack-best-practices
+description: Provides best practices and guidance for working with Rush monorepos. Use when the user is working in a Rush-based repository, asks about Rush commands (install, update, build, rebuild), needs help with project selection, dependency management, build caching, subspace configuration, or troubleshooting Rush-specific issues.
+license: MIT
+metadata:
+  author: rushstack
+  version: "1.0.0"
+---
+
+# Rushstack Best Practices
+
+This skill provides essential best practices for working with Rush monorepos. Following these guidelines ensures efficient dependency management, optimal build performance, and proper command usage.
+
+## Important Guidelines
+
+**When encountering unclear issues or questions:**
+
+1. **Never make assumptions** - If unsure about Rush behavior, configuration, or commands
+2. **Search official resources first** - Check documentation and existing issues before guessing
+3. **Provide accurate information** - Base responses on verified sources, not assumptions
+4. **Ask for clarification** - When the problem description is ambiguous or incomplete
+
+## Core Principles
+
+1. **Always use Rush commands** - Avoid npm/pnpm/yarn directly in a Rush monorepo
+2. **Use rushx for single projects** - Like npm run, but Rush-aware
+3. **rush install vs update** - install for CI, update after changes
+4. **rush build vs rebuild** - build for incremental, rebuild for clean
+5. **Projects at 2 levels** - Standard: apps/, libraries/, tools/
+6. **Selection flags reduce scope** - Use --to, --from, --impacted-by
+7. **Build cache is automatic** - Configure output folders to enable
+8. **Subspace for large repos** - Isolate dependencies when needed
+
+## Project Selection Best Practices
+
+When running commands like `install`, `update`, `build`, `rebuild`, etc., by default all projects under the entire repository are processed. Use these selection flags to improve efficiency:
+
+### --to <PROJECT>
+Select specified project and all its dependencies.
+- Build specific project and its dependencies
+- Ensure complete dependency chain build
+```bash
+rush build --to @my-company/my-project
+rush build --to my-project  # If project name is unique
+rush build --to .            # Use current directory's project
+```
+
+### --to-except <PROJECT>
+Select all dependencies of specified project, but not the project itself.
+- Update project dependencies without processing project itself
+- Pre-build dependencies
+```bash
+rush build --to-except @my-company/my-project
+```
+
+### --from <PROJECT>
+Select specified project and all its downstream dependencies.
+- Validate changes' impact on downstream projects
+- Build all projects affected by specific project
+```bash
+rush build --from @my-company/my-library
+```
+
+### --impacted-by <PROJECT>
+Select projects that might be affected by specified project changes, excluding dependencies.
+- Quick test of project change impacts
+- Use when dependency status is already correct
+```bash
+rush build --impacted-by @my-company/my-library
+```
+
+### --impacted-by-except <PROJECT>
+Similar to `--impacted-by`, but excludes specified project itself.
+- Project itself has been manually built
+- Only need to test downstream impacts
+```bash
+rush build --impacted-by-except @my-company/my-library
+```
+
+### --only <PROJECT>
+Only select specified project, completely ignore dependency relationships.
+- Dependency status is known to be correct
+- Combine with other selection parameters
+```bash
+rush build --only @my-company/my-project
+rush build --impacted-by projectA --only projectB
+```
+
+## Command Usage Guidelines
+
+### Command Tool Selection
+
+Choose the correct command tool based on different scenarios:
+
+1. **`rush` command** - Execute operations affecting the entire repository or multiple projects
+   - Strict parameter validation and documentation
+   - Support for global and batch commands
+   - Suitable for standardized workflows
+   - Use cases: Dependency installation, building, publishing
+
+2. **`rushx` command** - Execute specific scripts for a single project
+   - Similar to `npm run` or `pnpm run`
+   - Uses Rush version selector for toolchain consistency
+   - Prepares shell environment based on Rush configuration
+   - Use cases: Running project-specific build scripts, tests, dev servers
+
+3. **`rush-pnpm` command** - Replace direct use of pnpm in Rush repository
+   - Sets correct PNPM workspace context
+   - Supports Rush-specific enhancements
+   - Provides compatibility checks with Rush
+   - Use cases: When direct PNPM commands are needed
+
+### Install vs Update
+
+| Command | Behavior | When to Use |
+|---------|----------|-------------|
+| `rush update` | Updates shrinkwrap, installs new dependencies | After cloning, after git pull, after modifying package.json |
+| `rush install` | Read-only install from existing shrinkwrap | CI/CD pipelines, ensuring version consistency |
+
+### Build vs Rebuild
+
+| Command | Behavior | When to Use |
+|---------|----------|-------------|
+| `rush build` | Incremental build, only changed projects | Daily development, quick validation |
+| `rush rebuild` | Clean build all projects | Complete rebuild needed, investigating issues |
+
+## Dependency Management
+
+### Package Manager Selection
+Choose in `rush.json`:
+```json
+{
+  "pnpmVersion": "8.x.x"     // Preferred - efficient, strict
+  // "npmVersion": "8.x.x"   // Alternative
+  // "yarnVersion": "1.x.x"  // Alternative
+}
+```
+
+### Version Constraints
+Configure in `common/config/subspaces/<subspace>/common-versions.json`:
+```json
+{
+  "preferredVersions": {
+    "react": "17.0.2",
+    "typescript": "~4.5.0"
+  },
+  "implicitlyPreferredVersions": true,
+  "allowedAlternativeVersions": {
+    "typescript": ["~4.5.0", "~4.6.0"]
+  }
+}
+```
+
+### Adding/Removing Dependencies
+Always use Rush commands, not npm/pnpm directly:
+```bash
+rush add -p lodash --dev      # Add dev dependency
+rush add -p react --exact     # Add exact version
+rush remove -p lodash         # Remove dependency
+```
+
+## Build Cache Configuration
+
+Configure in `<project>/config/rush-project.json`:
+```json
+{
+  "operationSettings": [
+    {
+      "operationName": "build",
+      "outputFolderNames": ["lib", "dist"],
+      "disableBuildCacheForOperation": false,
+      "dependsOnEnvVars": ["MY_ENV_VAR"]
+    }
+  ]
+}
+```
+
+**Cache Behavior:**
+- Cache stored in `common/temp/build-cache`
+- Invalidated by: source changes, dependency changes, env vars, command params
+- Parallel builds supported via `enableParallelism`
+
+## Troubleshooting
+
+### Dependency Issues
+- Avoid `npm`, `pnpm`, `yarn` - use Rush commands
+- Run `rush purge` to clean environment
+- Run `rush update --recheck` to force dependency check
+
+### Build Issues
+- Use `rush rebuild` to skip cache
+- Check `rushx build` output for specific errors
+- Use `--verbose` for detailed logs
+
+### Performance Issues
+- Use selection flags (`--to`, `--from`, etc.) to reduce scope
+- Enable build cache in rush-project.json
+- Consider subspace for very large monorepos
+
+## Subspace for Large Monorepos
+
+**What is Subspace:**
+- Allows multiple PNPM lock files in one Rush monorepo
+- Enables independent dependency management per team/project group
+- Reduces risk from dependency updates
+- Improves install/update performance
+
+**When to Use:**
+- Large monorepos (50+ projects)
+- Multiple teams with different dependency needs
+- Conflicting version requirements
+- Need for faster dependency operations
+
+## Official Resources
+
+### Documentation & References
+
+**Official Websites:**
+- [RushStack.io](https://rushstack.io/) - Main documentation site
+- [Rush.js.io](https://rushjs.io/) - Rush build orchestrator documentation
+- [Heft.rushstack.io](https://heft.rushstack.io/) - Heft build tool documentation
+- [API Extractor](https://api-extractor.com/) - API documentation and rollups
+
+**Search Existing Issues:**
+- Before creating new issues, search [rush-stack-builds issues](https://github.com/microsoft/rushstack/issues)
+
+### When to Search vs. Ask
+
+**Search these resources first when:**
+- Encountering error messages
+- Unsure about configuration options
+- Looking for examples or tutorials
+- Need to understand Rush behavior
+
+**Ask the user for clarification when:**
+- The specific use case is unclear
+- Multiple approaches are possible
+- Context is missing to provide accurate guidance
+- The issue might be environment-specific
+
+## Detailed References
+
+For expanded information on specific domains, see:
+- `references/core-commands.md` - Detailed command reference
+- `references/project-configuration.md` - Configuration file specifications
+- `references/dependency-management.md` - Advanced dependency patterns
+- `references/build-system.md` - Build optimization and caching
+- `references/subspace.md` - Subspace setup and usage