activeId clears the instant the pointer is released, so gating the
focus-refresh on it alone left a window between drop and server
confirmation where a refresh could overwrite the optimistic position with
stale state and the card would appear to snap back. Tracks a separate
saving flag, and reverts on a thrown fetch as well as a non-ok response.
Also corrects a comment: sensors are created unconditionally; what keeps a
client manager from dragging is that they never render DndContext.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
