Window::onMouseScroll now fires on every backend and speaks one unit:
signed whole detents packed in the uint32 payload, +1 = wheel down
(DOM deltaY sign).
- Wayland: implement the previously-stubbed PointerListenerHandleAxis —
vertical axis only, wl_fixed_to_double / 15 (libinput's units-per-
detent), sub-detent remainder accumulated and reset on pointer leave.
- Win32: add the missing WM_MOUSEWHEEL case — -GET_WHEEL_DELTA_WPARAM /
WHEEL_DELTA with a remainder accumulator for free-spinning wheels.
- DOM: dom-env.js normalizes WheelEvent.deltaY per deltaMode (100px /
3 lines / 1 page per detent) with the same remainder scheme, so wasm
delivers the identical unit instead of raw browser-specific deltas.
- Document the contract on Window::onMouseScroll.
- tests/MouseScroll: compositor-free regression test driving the
Wayland axis handler directly.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
