SoundSource

A list rather than one path so a slot can accept whatever format the sound actually arrives in. Asking a composer to transcode before they can hear their track in the game is friction with nothing on the other side of it — the browser decodes all of these natively.

Omitted, the slot is required. A stand-in is right for a footstep and wrong for a score that has to be the file or nothing a game would ship, which until now could not be registered at all and was decoded outside the registry. A required slot none of whose candidates loads is recorded in unbuilt, and load rejects — after every other slot has settled, so one absent file still silences nothing else — naming each such slot and what it tried.