Scroll the chat by request, not by forcing a layout

The chat keeps its newest message in view when it opens and while the
keyboard slides, and both did it with `listState.scrollToItem`, which forces
a layout on the spot. This screen is composed inside the Scaffold's measure
pass, so when the effect ran straight away it asked for a layout in the
middle of one:

  IllegalArgumentException: performMeasureAndLayout called during measure layout
    at LayoutNode.forceRemeasure
    at LazyListState.snapToItemIndexInternal
    at ChatScreens.kt:1740 (the keyboard follow)
    ... LaunchedEffectImpl.onRemembered ... SubcomposeLayout ... Scaffold

It failed ChatFlowTest's send in every full on-device run since 2026-09-18.
The frames that ran the effect inline are the Compose test dispatcher's; the
shipped app posts effects to the next frame, so this has not been seen to
crash a real device. Forcing a synchronous layout from an effect is wrong
either way.

Both now use `requestScrollToItem` (foundation 1.7.6), which the next layout
applies, and the keyboard is what brings that layout. Still instant, still
not animated. The animated follow for new messages is unchanged: it waits
for animation frames before it moves.

TheKeyboardDoesNotHideTheMessagesTest read the source for
`listState.scrollToItem(`; it now requires `requestScrollToItem(` and refuses
`scrollToItem(` in the keyboard effect. Put the old line back and it fails.

Result on relay1: the full on-device suite passes, 10 of 10, and the crash
buffer has no performMeasureAndLayout. App unit tests: 358 debug, 323
release, all green.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/src/main/kotlin/io/flamenet/messenger/app/ChatScreens.kt

@@ -1715,8 +1715,17 @@ fun ColumnScope.ChatScreen(
     val listState = rememberLazyListState()
 
     // Open AT the newest message, a jump, not a tour of the history.
+    //
+    // `requestScrollToItem`, not `scrollToItem`, here and for the keyboard
+    // below. `scrollToItem` forces a layout on the spot, and this screen is
+    // composed inside the Scaffold's MEASURE pass, so an effect that runs
+    // straight away asks for a layout in the middle of one:
+    // "performMeasureAndLayout called during measure layout", thrown from the
+    // keyboard effect in the on-device suite (ChatFlowTest, 2026-09-18 to
+    // 09-28). The request is applied by the next layout instead, which comes
+    // at once because the keyboard is what is changing the layout.
     LaunchedEffect(Unit) {
-        if (chat.lines.isNotEmpty()) listState.scrollToItem(chat.lines.lastIndex)
+        if (chat.lines.isNotEmpty()) listState.requestScrollToItem(chat.lines.lastIndex)
     }
     // Follow the conversation as it grows.
     LaunchedEffect(chat.lines.size) {
@@ -1737,7 +1746,7 @@ fun ColumnScope.ChatScreen(
     // of that lands short by however much the viewport shrank afterwards.
     val imeBottom = WindowInsets.ime.getBottom(LocalDensity.current)
     LaunchedEffect(imeBottom) {
-        if (chat.lines.isNotEmpty()) listState.scrollToItem(chat.lines.lastIndex)
+        if (chat.lines.isNotEmpty()) listState.requestScrollToItem(chat.lines.lastIndex)
     }
 
     // One bar, not three stacked rows, and it wears the channel's own colour.

app/src/test/kotlin/io/flamenet/messenger/app/TheKeyboardDoesNotHideTheMessagesTest.kt

@@ -58,10 +58,19 @@ class TheKeyboardDoesNotHideTheMessagesTest {
         // The inset arrives as a series of values while the keyboard slides.
         // One animated jump fired at the start of that lands short by however
         // much the viewport shrank afterwards.
+        //
+        // Instant means `requestScrollToItem`, applied by the next layout, and
+        // NOT `scrollToItem`, which forces a layout on the spot: this screen is
+        // composed inside the Scaffold's measure pass, and on-device that threw
+        // "performMeasureAndLayout called during measure layout".
         val block = screens.substringAfter("LaunchedEffect(imeBottom) {").substringBefore("}")
         assertTrue(
-            block.contains("listState.scrollToItem("),
+            block.contains("listState.requestScrollToItem("),
-            "the keyboard follow should scroll instantly: $block",
+            "the keyboard follow should scroll instantly, by request: $block",
+        )
+        assertTrue(
+            !block.contains("listState.scrollToItem("),
+            "scrollToItem forces a layout and throws when it runs inside one: $block",
         )
         assertTrue(
             !block.contains("animateScrollToItem"),