test(island): the pass's aim is read once the band stands at it

services/frontend/tests/e2e/boards-swipe.motion.spec.ts

@@ -184,7 +184,7 @@ test.describe("dragging the board page", () => {
     // The pass a finger plays measures the board it is dragging in, which is drawn open — the
     // axis is claimed before it is mounted — so the figure it aims at is the finished layout.
     await dragBand(page, band, {by: 260})
-    const swiped = await aimedAt(page, SWIPE)
+    const swiped = await aimedAt(page, SWIPE, from)
     await expect(page).toHaveURL(/\?board=2$/)
 
     // Aimed at a real difference rather than at the height it already stood at, which is what
@@ -198,7 +198,7 @@ test.describe("dragging the board page", () => {
     // The pass the band plays for itself, a stop arriving without a gesture, aims at the same
     // thing: it measures the arriving board a frame after it was built, and it was built open.
     await page.getByTestId("board-node-5").click()
-    const hit = await aimedAt(page, SWIPE)
+    const hit = await aimedAt(page, SWIPE, swiped)
     await expect(page.getByTestId("board-band-name")).toHaveText("Eeveelutions")
 
     expect(Math.abs(hit - swiped)).toBeGreaterThan(HAIR)

services/frontend/tests/e2e/sliceBand.ts

@@ -138,12 +138,18 @@ export function heldHeight(page: Page, swipe: string): Promise<number | null> {
  * Both of the band's height animations set the resting height on the element before animating
  * over it, so what is written there is the end of the pass stated at the start of it — which is
  * the intention, where a height sampled mid-pass is only a frame of one.
+ *
+ * A pass that swaps the stop pins the height it is leaving first, a tick before it can measure
+ * the one it is arriving at, so the first inline height there is where the band was rather than
+ * where it is going. [stoodAt] is the height it is leaving, and tells the two apart.
  */
-export async function aimedAt(page: Page, swipe: string): Promise<number> {
-  const handle = await page.waitForFunction((sel) => {
+export async function aimedAt(page: Page, swipe: string, stoodAt: number): Promise<number> {
+  const handle = await page.waitForFunction(([sel, held]) => {
     const aim = (document.querySelector(sel) as HTMLElement | null)?.style.height
-    return aim ? Math.round(parseFloat(aim)) : null
-  }, swipe)
+    if (!aim) return null
+    const px = Math.round(parseFloat(aim))
+    return px === held ? null : px
+  }, [swipe, stoodAt] as const)
   return handle.jsonValue()
 }