fix(app): stabilize session timeline layout continuity (#34533)

packages/app/e2e/utils/visual-stability/regions.ts

@@ -0,0 +1,18 @@
+export type VisualRegionDefinition = {
+  selector: string
+  closest?: string
+  opacitySelectors?: readonly string[]
+}
+
+export function defineVisualRegions<const Regions extends Record<string, VisualRegionDefinition>>(regions: Regions) {
+  return regions
+}
+
+export function mapVisualRegions<const Regions extends Record<string, VisualRegionDefinition>, Result>(
+  regions: Regions,
+  map: (region: Regions[keyof Regions], name: keyof Regions) => Result,
+) {
+  return Object.fromEntries(
+    Object.entries(regions).map(([name, region]) => [name, map(region as Regions[keyof Regions], name)]),
+  ) as { [Name in keyof Regions]: Result }
+}