fix(styles): keep Snow wind sway bounded over time (#782)

The horizontal offset multiplied elapsed time by a sine, so flakes swung faster the longer the app ran. It is now the integral of the intended sway velocity, which stays bounded at any session age; Wind still scales the amplitude.

Co-authored-by: Sameh Khamis <[email protected]>

CHANGELOG.md

@@ -1,5 +1,8 @@
 # Changelog
 
+- Snow flakes sway within a fixed range instead of drifting sideways faster the
+  longer the app runs; the Wind setting still scales the sway.
+
 - The right rail ignores panels that other CSS hides, such as during an event
   view, so they no longer force one-panel-at-a-time layout or collapse visible
   panels. Panels the rail collapses itself are still restored.

docs/CURRENT-STATE.md

@@ -1013,6 +1013,8 @@ and sharpen. Display supplies actions and renders settings; effect execution has
 no DOM dependency. Existing presets and the 500 ms transition remain unchanged.
 Stopping the controller revokes animation before asynchronous UI teardown; final
 destruction removes its stages and restores the borrowed bloom configuration.
+Snow's sideways sway stays within a fixed range at any session age; Wind scales
+its amplitude.
 
 ## Display control ownership
 

src/styles/snow.js

@@ -29,11 +29,13 @@ export const snowShader = {
       float depth = 0.5 + layer * 0.5;
       float speed = 0.4 + layer * 0.3;
       float size = mix(0.01, 0.025, layer);
-      float windForce = sin(time * 0.5 + layer * 3.14) * (0.05 + wind * 0.2);
+      float windForce = 0.05 + wind * 0.2;
 
       vec2 snowUV = uv * vec2(1.0, 0.5) * (4.0 + layer * 4.0);
       snowUV.y += time * speed;
-      snowUV.x += time * windForce;
+      // Offset is the integral of a swaying velocity sin(time * 0.5 + phase) * windForce,
+      // so the sway stays bounded however long the app has been running.
+      snowUV.x -= 2.0 * cos(time * 0.5 + layer * 3.14) * windForce;
 
       vec2 cell = floor(snowUV);
       vec2 f = fract(snowUV);