diff --git a/app/androidApp/src/main/kotlin/com/example/aiapp/Markdown.kt b/app/androidApp/src/main/kotlin/com/example/aiapp/Markdown.kt
index f9ae47b..1e226c5 100644
--- a/app/androidApp/src/main/kotlin/com/example/aiapp/Markdown.kt
+++ b/app/androidApp/src/main/kotlin/com/example/aiapp/Markdown.kt
@@ -3,6 +3,7 @@ package com.example.aiapp
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.Stable
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Modifier
@@ -166,6 +167,7 @@ private fun parsedMarkdown(text: String, replies: ParsedReplies): State {
  * itself on the way to being finished. It is dropped with the screen, and emptied by the stream
  * reset that drops the rows it describes.
  */
+@Stable
 class ParsedReplies {
     private val parsed = ConcurrentHashMap<String, State>()
 
diff --git a/app/androidApp/src/main/kotlin/com/example/aiapp/MemoryNote.kt b/app/androidApp/src/main/kotlin/com/example/aiapp/MemoryNote.kt
index d5a7808..995bdb8 100644
--- a/app/androidApp/src/main/kotlin/com/example/aiapp/MemoryNote.kt
+++ b/app/androidApp/src/main/kotlin/com/example/aiapp/MemoryNote.kt
@@ -27,6 +27,7 @@ import androidx.compose.ui.unit.dp
  */
 @Composable
 fun AssistantMessage(text: String, replies: ParsedReplies, modifier: Modifier = Modifier) {
+    DebugStats.count("message composed")
     val parts = remember(text) { partsOf(text) }
     val only = parts.singleOrNull()
     if (only is MessagePart.Prose) {
diff --git a/app/androidApp/src/main/kotlin/com/example/aiapp/SessionScreen.kt b/app/androidApp/src/main/kotlin/com/example/aiapp/SessionScreen.kt
index ab78a69..27fce6a 100644
--- a/app/androidApp/src/main/kotlin/com/example/aiapp/SessionScreen.kt
+++ b/app/androidApp/src/main/kotlin/com/example/aiapp/SessionScreen.kt
@@ -35,6 +35,7 @@ import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.DisposableEffect
+import androidx.compose.runtime.Immutable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
@@ -179,6 +180,7 @@ private fun Modifier.holdTopEdge(key: Any, held: TopEdgeHold, hold: (Int) -> Uni
  * stream is the only data source -- opening this screen replays from seq 0, and a reconnect resumes
  * from the last seq seen, so there is no separate history fetch to drift from it.
  */
+@Immutable
 sealed class TranscriptItem {
     /**
      * The transcript sequence number this row started at, and its identity on screen.
diff --git a/app/androidApp/src/main/kotlin/com/example/aiapp/ToolRows.kt b/app/androidApp/src/main/kotlin/com/example/aiapp/ToolRows.kt
index af8833f..69fb472 100644
--- a/app/androidApp/src/main/kotlin/com/example/aiapp/ToolRows.kt
+++ b/app/androidApp/src/main/kotlin/com/example/aiapp/ToolRows.kt
@@ -18,6 +18,7 @@ import androidx.compose.material3.CircularProgressIndicator
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.Immutable
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
@@ -38,6 +39,19 @@ import androidx.compose.ui.unit.dp
  * the transcript's own order is what paging and the event stream depend on, and one screen's idea
  * of "these belong together" must not reach back into it.
  */
+/**
+ * Immutable, and said so, because Compose cannot tell.
+ *
+ * A row is a value: it is rebuilt from the transcript rather than edited, and two rows describing
+ * the same events are equal. Compose infers stability from a class's fields, and a `List` field --
+ * which several of these carry -- makes it assume the worst, so every composable taking one
+ * recomposed whenever anything above it did. A page of history landing recomposed all 148 loaded
+ * rows including the markdown inside them, measured as 701 compositions for 148 rows in one scroll,
+ * and that is what a page landing costs on top of the fetch itself.
+ *
+ * The promise this makes is real and has to stay true: nothing here is mutated after it is built.
+ */
+@Immutable
 sealed class TranscriptRow {
     /**
      * This row's identity in the list, which must survive everything that can happen to the row.