Fix Codex transcript convergence

app/androidApp/src/main/kotlin/com/example/aiapp/TranscriptItems.kt

@@ -63,6 +63,8 @@ sealed class TranscriptItem {
          * inside that reply would step the list under them.
          */
         val settled: Boolean = false,
+        /** A final value that supersedes provisional deltas behind a page boundary. */
+        val replacesPrefix: Boolean = false,
     ) : TranscriptItem()
 
     data class ToolRun(
@@ -308,6 +310,7 @@ private fun healSplitMessage(
     // The rule between them is put in here too, since the fold that would have made it never saw
     // these two side by side.
     if (head.settled) return earlier to (listOf(TranscriptItem.TurnBreak(tail.seq)) + later)
+    if (tail.replacesPrefix) return earlier.dropLast(1) to later
     return earlier.dropLast(1) to (listOf(tail.copy(text = head.text + tail.text)) + later.drop(1))
 }
 
@@ -411,6 +414,24 @@ fun foldEvent(items: List<TranscriptItem>, entry: SeqEvent): List<TranscriptItem
                 items + between + TranscriptItem.AssistantMsg(entry.seq, event.delta)
             }
         }
+        is SessionEvent.AssistantTextFinal -> {
+            val last = items.lastOrNull()
+            if (last is TranscriptItem.AssistantMsg && !last.settled) {
+                items.dropLast(1) + last.copy(text = event.text, replacesPrefix = true)
+            } else {
+                val between =
+                    if (last is TranscriptItem.AssistantMsg)
+                        listOf(TranscriptItem.TurnBreak(entry.seq))
+                    else emptyList()
+                items +
+                    between +
+                    TranscriptItem.AssistantMsg(
+                        entry.seq,
+                        event.text,
+                        replacesPrefix = true,
+                    )
+            }
+        }
         is SessionEvent.ToolStart ->
             items +
                 TranscriptItem.ToolRun(