feat: render display_kind timeline markers as chips, not user bubbles (#904) (#909)

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/test/java/com/m57/hermescontrol/data/local/ChatMessageMapperTest.kt

@@ -161,4 +161,36 @@ class ChatMessageMapperTest {
 
         assertEquals("r", roundTripped.reasoningText)
     }
+
+    @Test
+    fun roundTripPreservesDisplayKind() {
+        val ui =
+            ChatMessage(
+                id = "msg-4",
+                role = MessageRole.USER,
+                content = "[System: ...changed to gpt-5...]",
+                displayKind = "model_switch",
+                timestamp = 4000L,
+            )
+
+        val roundTripped = ui.toEntity("s").toUiModel()
+
+        assertEquals("model_switch", roundTripped.displayKind)
+        assertEquals(MessageRole.USER, roundTripped.role)
+    }
+
+    @Test
+    fun roundTripWithoutDisplayKindStaysNull() {
+        val ui =
+            ChatMessage(
+                id = "msg-5",
+                role = MessageRole.USER,
+                content = "plain user text",
+                timestamp = 5000L,
+            )
+
+        val roundTripped = ui.toEntity("s").toUiModel()
+
+        assertNull(roundTripped.displayKind)
+    }
 }

app/src/test/java/com/m57/hermescontrol/data/model/ModelSerializationTest.kt

@@ -4,6 +4,7 @@ import com.m57.hermescontrol.data.remote.OkHttpProvider
 import kotlinx.serialization.decodeFromString
 import kotlinx.serialization.encodeToString
 import kotlinx.serialization.json.JsonElement
+import kotlinx.serialization.json.JsonObject
 import kotlinx.serialization.json.JsonPrimitive
 import kotlinx.serialization.json.booleanOrNull
 import org.junit.Assert.assertEquals
@@ -420,6 +421,49 @@ class ModelSerializationTest {
         assertNull(response.disk?.free_mb)
     }
 
+    @Test
+    fun testSessionMessageDeserialization_displayKindMarker() {
+        val jsonStr =
+            """
+            {
+                "id": 42,
+                "role": "user",
+                "content": "[System: The active model for this chat has changed to gpt-5 via provider openai. From this point forward, use this runtime metadata when answering questions about what model/provider is active.]",
+                "timestamp": 1755260000000,
+                "display_kind": "model_switch",
+                "display_metadata": {
+                    "delegation_id": "dlg-1",
+                    "task_count": 3
+                }
+            }
+            """.trimIndent()
+        val message = json.decodeFromString<SessionMessage>(jsonStr)
+        assertEquals(42, message.id)
+        assertEquals("user", message.role)
+        assertEquals("model_switch", message.display_kind)
+        val metadata = message.display_metadata
+        assertNotNull(metadata)
+        val delegationId =
+            (metadata as? JsonObject)?.get("delegation_id") as? JsonPrimitive
+        assertEquals("dlg-1", delegationId?.content)
+    }
+
+    @Test
+    fun testSessionMessageDeserialization_missingDisplayKind() {
+        val jsonStr =
+            """
+            {
+                "id": 7,
+                "role": "assistant",
+                "content": "hi"
+            }
+            """.trimIndent()
+        val message = json.decodeFromString<SessionMessage>(jsonStr)
+        assertEquals(7, message.id)
+        assertNull(message.display_kind)
+        assertNull(message.display_metadata)
+    }
+
     @Test
     fun testStatusResponseDeserialization_typeMismatchInGatewayPlatforms() {
         val jsonStr =