AC-OS folded multitouch into a single pointer: ABS_MT_POSITION_X/Y nudged pointer_x/y relatively, with no slot state at all. A drum head needs the whole hand — the fingers resting on it damp the modes the striking one excites — so contacts now accumulate into MT-B slots and commit as a set at SYN_REPORT, which is also the only frame where a strike and its damping fingers can be read together. Two things fall out of having real slots. The pointer follows the primary contact alone instead of summing every finger's absolute jumps, so resting a second finger no longer makes the cursor bolt across the screen. And trackpad detection asks INPUT_PROP_DIRECT rather than guessing from axis range, which had been calling the touchscreen on a convertible a trackpad. Unplug compaction shifted fds and fd_is_analog but not fd_is_trackpad, leaving the flag pointing at the wrong device; it now shifts with them. tools/surface-audit.c replays a synthetic MT-B stream through the tracker.