fix: complete retail parity stability pass

docs/plans/2026-07-27-vulkan-campaign.md

@@ -503,6 +503,12 @@ elapsed seconds that `TexVelocityX/Y` accumulate against with a fixed value.
 **Unset — the default, and every ordinary run — keeps the wall clock**, so
 nothing the user or the offline gate sees changes unless a gate asks.
 
+**2026-08-28 follow-up:** the ordinary sky-animation source is now a monotonic
+`Stopwatch` clock, matching retail's accumulated timer deltas and preventing an
+OS time correction from jumping rain/cloud UVs. The V7 pin and its gate
+semantics are unchanged; the wall-clock wording above describes the original
+V7 implementation.
+
 It exists because `ACDREAM_DAY_GROUP` and the `AcdreamCycleTimeOfDay` override
 pin only the *other* sky clock: the Dereth date, which chooses the day group,
 the keyframe and the sun angle. The cloud sheet does not read that clock at all
@@ -2591,6 +2597,10 @@ Holtburg pair went from 23,090 differing pixels to 1,211. **The alternative was
 `-MaskTopPixels`, which would have permanently blinded the campaign's strictest
 instrument to the entire sky.** See §5.1.
 
+The 2026-08-28 rain-timing parity follow-up replaced that adjustable wall clock
+with monotonic `Stopwatch` elapsed time; this historical V7 measurement and the
+diagnostic pin remain otherwise unchanged.
+
 **3. The world clock was never pinned at all, and that was most of the number**
 (`1f25a609`). The route opened by pressing `AcdreamCycleTimeOfDay` three times.
 The mechanism underneath is `WorldTimeService.SetDebugTime`, and