fix(marko-virtual): hold chat-pretext pin through in-flight prepends, harden scroll-settle waits.

Author: piecyk

examples/marko/chat-pretext/src/routes/+page.marko

@@ -193,12 +193,14 @@ static function messageHeight(message: Message, viewportWidth: number) {
         atEnd = statusEl.scrollHeight - statusEl.scrollTop - statusEl.clientHeight <= AT_END_PX
       }
       // Converge an in-flight "Latest": re-issue the jump while content growth keeps
-      // moving the end away (see pinPending above). Terminates as soon as the end
-      // holds through one virtualizer update.
+      // moving the end away (see pinPending above). Disarms once the end holds AND no
+      // history load is in flight — a prepend armed before the click can land after
+      // the end was first reached, and disarming early would leave that late growth
+      // with no corrective jump.
       if (state.pinPending) {
-        if (atEnd) {
+        if (atEnd && !loadingHistory) {
           state.pinPending = false
-        } else {
+        } else if (!atEnd) {
           v.scrollToEnd()
         }
       }

packages/marko-virtual/e2e/app/e2e/chat-pretext.spec.ts

@@ -57,16 +57,21 @@ async function scrollTop(page: Page): Promise<number> {
 // virtualizer is still measuring the rows that came into view, and a measured size
 // above the viewport makes core compensate the offset. A baseline captured mid-settle
 // makes the "this action did NOT move the view" assertion race. Same helper as
-// chat.spec.ts; the two pages share this shape.
+// chat.spec.ts; the two pages share this shape. Requires several consecutive stable
+// samples: a single unchanged pair can straddle a pause between two compensation
+// steps under load, reading as settled mid-drift.
 async function waitForScrollSettled(page: Page) {
   let previous = Number.NaN
+  let stableSamples = 0
   await expect
     .poll(
       async () => {
         const current = await scrollTop(page)
-        const settled = current === previous
+        const stable =
+          !Number.isNaN(previous) && Math.abs(current - previous) <= 0.5
+        stableSamples = stable ? stableSamples + 1 : 0
         previous = current
-        return settled
+        return stableSamples >= 3
       },
       { timeout: 5000, intervals: [100, 100, 100, 150, 150, 200] },
     )

packages/marko-virtual/e2e/app/e2e/chat.spec.ts

@@ -58,15 +58,20 @@ async function scrollTop(page: Page): Promise<number> {
 // the viewport makes core compensate the offset — so a baseline captured immediately
 // after the jump can still drift by ~100px on its own. Tests that assert "this
 // action did NOT move the view" need a quiescent baseline, or they race the settle.
+// Requires several consecutive stable samples: a single unchanged pair can straddle
+// a pause between two compensation steps under load, reading as settled mid-drift.
 async function waitForScrollSettled(page: Page) {
   let previous = Number.NaN
+  let stableSamples = 0
   await expect
     .poll(
       async () => {
         const current = await scrollTop(page)
-        const settled = current === previous
+        const stable =
+          !Number.isNaN(previous) && Math.abs(current - previous) <= 0.5
+        stableSamples = stable ? stableSamples + 1 : 0
         previous = current
-        return settled
+        return stableSamples >= 3
       },
       { timeout: 5000, intervals: [100, 100, 100, 150, 150, 200] },
     )