project property

Which project this address belongs to, or null for "the one the session reading it was launched in" — which is every address anything emits today, since a shell is opened on one repo and discovers that repo's worktrees.

Reserved rather than used. It exists because a fw:// link followed from a browser or a chat window arrives at an installed flutterware knowing nothing about which checkout it is for, and that is precisely the question a URI authority answers. Adding the slot later would have meant reparsing every address ever written down.