Item Management skill: what it does and how to install it

What it does. Explains MSBuild item operations and expressions, including adding, removing and updating items, filtering with conditions, transforms and metadata-based batching. It gives patterns for avoiding cross-product batching and duplicate items, and covers item-related generated-file and clean-tracking concerns.

When to use it. For concrete MSBuild questions or reviews involving item identity, metadata, declarations, globs, transforms or batching. It does not cover property-only issues, general incrementality without an item question, or non-MSBuild systems.