Command, cwd, pinned account home, and the thread to resume all come back
out of the record the lease already wrote, never from the client-declared
identity: a caller that could name the thread could point a session at
someone else's conversation.
It refuses rather than guesses — a record pinned to another execution host or
a WSL distro is not this host's to spawn for, a record for another provider or
another account-home variable is not this adapter's to speak for, and a
workspace that no longer resolves surfaces instead of falling back to a
default cwd.
