[Win] Curves preview lags / doesn't update until mouse release – regression after 27.3.1

Since updating past 27.3.1, dragging a point in a Curves adjustment (in the
Properties panel or with the on-canvas targeted adjustment tool) is extremely
laggy: the preview takes seconds to react, or often doesn't update at all
until I release the mouse.

- Last working version: 27.3.1
- First broken version: 27.4
- Still broken in: 27.11
- Photoshop 2025 (26.x) on the same machine: smooth

Steps to reproduce:
1. File > New, 2000x2000 px, 8-bit RGB
2. Add a Curves adjustment layer
3. Drag a curve point continuously

But it does with any single photo I throw at it. 

Expected: live preview while dragging (as in 27.3.1)
Actual: seconds of lag / no update until mouse release, either or

Already ruled out:
- Happens on a small, simple 8-bit document (not file-related)
- Same with GPU enabled and disabled
- Same with fresh preferences (settings folder removed)
- Same with third-party plug-ins disabled
- Same on both monitors (4K @150% and 1920x1200 @100%)
- Windows Auto Color Management / HDR off

Observation: while dragging, Photoshop's main thread sits at ~100% of one
CPU core while the GPU stays at 5–30% and the remaining cores are idle.

System: Windows 11 Home 25H2 (26200), AMD Ryzen 5 5600, 32 GB RAM,
NVIDIA RTX 3060 Ti 8 GB (driver 610.88), Samsung 980 PRO NVMe