Fix first Wear message auto-scroll

wear/src/main/java/com/bitchat/watch/ui/ChatScaffold.kt

@@ -113,9 +113,21 @@ fun ChatScaffold(
     val followNewest = remember(messages.size) { atNewest }
     LaunchedEffect(columnState, messages.size) {
         if (messages.isNotEmpty() && followNewest) {
+            val expectedSingleMessageKey = messages.singleOrNull()?.id
             scrollToNewestAfterItemsMeasured(
                 expectedItemCount = messages.size,
-                measuredItemCounts = snapshotFlow { columnState.layoutInfo.totalItemsCount }
+                expectedSingleMessageKey = expectedSingleMessageKey,
+                measuredLayouts = snapshotFlow {
+                    val layoutInfo = columnState.layoutInfo
+                    MeasuredChatLayout(
+                        itemCount = layoutInfo.totalItemsCount,
+                        singleVisibleItemKey = if (expectedSingleMessageKey != null) {
+                            layoutInfo.visibleItems.singleOrNull()?.key
+                        } else {
+                            null
+                        }
+                    )
+                }
             ) {
                 // scrollBy to the end of the range: animateScrollToItem stops as soon as the
                 // item is partially visible, which left the last message cropped.
@@ -138,12 +150,22 @@ fun ChatScaffold(
     )
 }
 
+internal data class MeasuredChatLayout(
+    val itemCount: Int,
+    val singleVisibleItemKey: Any?
+)
+
 internal suspend fun scrollToNewestAfterItemsMeasured(
     expectedItemCount: Int,
-    measuredItemCounts: Flow<Int>,
+    expectedSingleMessageKey: Any?,
+    measuredLayouts: Flow<MeasuredChatLayout>,
     scrollToEnd: suspend () -> Unit
 ) {
-    measuredItemCounts.first { it >= expectedItemCount }
+    measuredLayouts.first { layout ->
+        layout.itemCount >= expectedItemCount &&
+            (expectedSingleMessageKey == null ||
+                layout.singleVisibleItemKey == expectedSingleMessageKey)
+    }
     scrollToEnd()
 }
 

wear/src/test/java/com/bitchat/watch/ui/ChatAutoScrollTest.kt

@@ -12,13 +12,14 @@ class ChatAutoScrollTest {
 
     @Test
     fun `newest scroll waits until appended message is measured`() = runTest {
-        val measuredItemCount = MutableStateFlow(3)
+        val measuredLayouts = MutableStateFlow(MeasuredChatLayout(3, null))
         var scrollCount = 0
 
         val scrollJob = launch(start = CoroutineStart.UNDISPATCHED) {
             scrollToNewestAfterItemsMeasured(
                 expectedItemCount = 4,
-                measuredItemCounts = measuredItemCount
+                expectedSingleMessageKey = null,
+                measuredLayouts = measuredLayouts
             ) {
                 scrollCount += 1
             }
@@ -27,7 +28,7 @@ class ChatAutoScrollTest {
         assertFalse(scrollJob.isCompleted)
         assertEquals(0, scrollCount)
 
-        measuredItemCount.value = 4
+        measuredLayouts.value = MeasuredChatLayout(4, null)
         scrollJob.join()
 
         assertEquals(1, scrollCount)
@@ -35,16 +36,47 @@ class ChatAutoScrollTest {
 
     @Test
     fun `newest scroll runs immediately when messages are already measured`() = runTest {
-        val measuredItemCount = MutableStateFlow(4)
+        val measuredLayouts = MutableStateFlow(MeasuredChatLayout(4, null))
         var scrollCount = 0
 
         scrollToNewestAfterItemsMeasured(
             expectedItemCount = 4,
-            measuredItemCounts = measuredItemCount
+            expectedSingleMessageKey = null,
+            measuredLayouts = measuredLayouts
         ) {
             scrollCount += 1
         }
 
         assertEquals(1, scrollCount)
     }
+
+    @Test
+    fun `first message waits past stale empty placeholder layout`() = runTest {
+        val messageKey = "first-message"
+        val measuredLayouts = MutableStateFlow(
+            MeasuredChatLayout(itemCount = 1, singleVisibleItemKey = "empty-placeholder")
+        )
+        var scrollCount = 0
+
+        val scrollJob = launch(start = CoroutineStart.UNDISPATCHED) {
+            scrollToNewestAfterItemsMeasured(
+                expectedItemCount = 1,
+                expectedSingleMessageKey = messageKey,
+                measuredLayouts = measuredLayouts
+            ) {
+                scrollCount += 1
+            }
+        }
+
+        assertFalse(scrollJob.isCompleted)
+        assertEquals(0, scrollCount)
+
+        measuredLayouts.value = MeasuredChatLayout(
+            itemCount = 1,
+            singleVisibleItemKey = messageKey
+        )
+        scrollJob.join()
+
+        assertEquals(1, scrollCount)
+    }
 }