SendToQueue, Cancel, Refine, Planning and OpenWorktree each had a CanX property
and a hand-written negation of it for the DisabledReason tooltip, kept in sync
only by a comment's promise. Replace each pair with a private gate method
returning (Can, Reason) so there is one source of truth per condition, and add
a state-matrix test pinning down the CanX == (Reason == null) invariant that
the old comment only asserted.
Mika Kuns
baba921696