Dictionary<K,V>.Remove and HashSet<T>.Remove do not bump the collection
version, so removing during a foreach is safe and the collect-then-remove
queues guarding those loops are dead weight. This drops them, including
via the Keys and Values enumerators.
Deletion of a Mobile is left deferred: removing from World.Mobiles while
enumerating it is fine, but Delete() runs OnDelete/OnAfterDelete, the
OnParentDeleted cascade over the pack, and region and guild callbacks.
Anything in there that constructs a Mobile is an Add into the dictionary
being enumerated, which does invalidate it.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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