probeDy property

double get probeDy

Touch-first probe offset: shifts slot resolution from the raw pointer to the PROXY MIDPOINT, grabRowExtent / 2 - grabDy. On touch there is no visible cursor, so the card in hand is the only thing the user can steer by and selection has to track it. Non-zero only when the caller enables the midpoint probe (make-room plus release-settle, where the anchor IS the visible floating card) and the grab capture succeeded. A session constant, so the whole resolution pipeline simply probes at pointer + probeDy.

Derived invariant: at drag start the probe is the dragged row's OWN midpoint, because the grab position cancels out, so every probed session begins on the current-position target. For a drag started on a pinned header that holds only because resolveTarget consults the pinned-band lookup first (L21): the grab geometry is the pinned band's, and a positional lookup against structural offsets would answer with the content scrolled beneath the strip.

Implementation

double get probeDy => _probeDy;