fix(desktop): keep long live replies pinned

desktop/src/features/messages/ui/TimelineMessageList.tsx

@@ -440,8 +440,11 @@ function VirtualizedTimelineRows({
     (version: number) => version + 1,
     0,
   );
-  const { cancel: cancelBottomSettle, settle: settleAtBottom } =
-    useVirtualizedBottomSettle(hostRef, listRef, itemsLengthRef);
+  const {
+    cancel: cancelBottomSettle,
+    hasBottomIntent,
+    settle: settleAtBottom,
+  } = useVirtualizedBottomSettle(hostRef, listRef, itemsLengthRef);
   const { arm: armUpwardMomentum } = useUpwardPaginationWheel(
     hostRef,
     cancelBottomSettle,
@@ -549,14 +552,23 @@ function VirtualizedTimelineRows({
       // emit `onScroll` without any user input. Cancelling here strands the
       // channel above its newest message. The settle hook's wheel, pointer,
       // touch, and key listeners are the authoritative user-interaction gate.
-      onAtBottomStateChange?.(distanceFromBottom <= 32);
+      const atBottom = distanceFromBottom <= 32;
+      // Geometry remeasurement can emit an intermediate offset while the
+      // bottom-settle loop still owns the scroller. Reporting that transient as
+      // reader navigation freezes live arrivals until the user sends or jumps
+      // to the new-message pill. Only a real input transfer (which cancels
+      // bottom intent) may report a non-bottom state.
+      if (atBottom || !hasBottomIntent()) {
+        onAtBottomStateChange?.(atBottom);
+      }
       if (offset <= 200) {
         // Layout scrolls near the top must not poison the reader's next input.
         armUpwardMomentum(onStartReached?.() ?? false);
       }
     },
     [
       armUpwardMomentum,
+      hasBottomIntent,
       onAtBottomStateChange,
       onStartReached,
       onVirtualizerRangeChanged,

desktop/src/features/messages/ui/useVirtualizedBottomSettle.test.mjs

@@ -153,7 +153,9 @@ async function mountHarness() {
 
 test("bottom intent follows arbitrarily late virtual geometry changes", async () => {
   const { content, refs, root, scroller, writes } = await mountHarness();
+  assert.equal(refs.api.current.hasBottomIntent(), false);
   refs.api.current.settle();
+  assert.equal(refs.api.current.hasBottomIntent(), true);
   assert.deepEqual(writes, [{ index: 4, options: { align: "end" } }]);
 
   const geometryObserver = resizeObservers.find((observer) =>
@@ -195,6 +197,7 @@ for (const eventType of ["pointerdown", "touchmove", "wheel", "keydown"]) {
             : undefined,
       type: eventType,
     });
+    assert.equal(refs.api.current.hasBottomIntent(), false);
 
     resizeObservers
       .find((observer) => observer.targets?.includes(content))

desktop/src/features/messages/ui/useVirtualizedBottomSettle.ts

@@ -125,6 +125,8 @@ export function useVirtualizedBottomSettle(
     pinToBottom();
   }, [cancelFrame, pinToBottom]);
 
+  const hasBottomIntent = React.useCallback(() => bottomIntentRef.current, []);
+
   React.useEffect(() => cancel, [cancel]);
-  return { cancel, settle };
+  return { cancel, hasBottomIntent, settle };
 }