R1: UiRoot now delivers WM_CAPTURECHANGED (0x215 — retail's own Win32
event-id space) to the element losing pointer capture on BOTH release
and re-target; UiScrollbar terminates a mid-drag gesture there,
completing it (one DragCompleted flush persisting the user's last-seen
value) and unlatching IsDragging — a panel-close keybind mid-drag or a
second-button re-target can no longer latch the drag flag forever and
silently suppress every later settings flush. Normal MouseUp paths
no-op (the latch is already clear when capture releases).
R2: the scalar latch arms BEFORE the track-click jump applies, so the
jump's own ScalarChanged tick defers its flush to the MouseUp's single
DragCompleted — one flush per press gesture, never the
inline-then-completed double; the DragCompleted doc now states the real
contract (fires once per value-capable gesture incl. capture loss)
instead of the refuted never-on-jump claim.
Tests: capture-loss mid-drag (ends + completes once + stray-MouseUp
no-double), no-drag capture-change no-op, bare-track-click
single-completion with the latch observed armed during the jump tick.
Also reconciles the research doc's U4 row to its closure (the six
caption pairs, the BN zero-fold post-mortem) per the OP6 rework's flag.
Full Release suite: 13,128 passed / 4 skipped / 0 failed (one
documented #250-class allocation flake on first run, green in
isolation and on full-suite rerun).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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