Same gap as Ref: slotA -> slotB via State<Slot> matches the same
SlotHandler both times, so Dispatch skips retract and process must
diff. Slot's confirmed no-portal/discard-only policy makes an identity
short-circuit a correctness requirement, not just an optimization --
without it, any spurious same-value re-emit would tear down and
rebuild the entire mounted subtree.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
