Several messages used the player, the character or the user they named
without checking that there is one. A match request and a trade request
are now only handled for the player that sent them, a linked mission
request and a build mode change only for the sending player, and the
remaining handlers return when the player, character or user is
missing.
Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>