fix(ui): ignore malformed tool stream entries (#111145)

Prevent malformed transient tool-stream entries from aborting Control UI chat reconciliation while preserving valid tool message order and rendering.

ui/src/pages/chat/chat-thread.test.ts

@@ -1870,6 +1870,26 @@ describe("buildCachedChatItems", () => {
     expect(messageRecord(groupAt(groups, 0)).content).toBe("still visible");
   });
 
+  it("does not expose malformed tool stream entries to message rendering", () => {
+    const items = buildCachedChatItems(
+      createProps({
+        toolMessages: [
+          null,
+          undefined,
+          {
+            role: "assistant",
+            content: [{ type: "toolcall", name: "heartbeat_respond", arguments: {} }],
+            timestamp: 1,
+          },
+        ],
+      }),
+    );
+
+    const groups = items.filter((item) => item.kind === "group");
+    expect(groups).toHaveLength(1);
+    expect(messageRecord(groupAt(groups, 0)).role).toBe("assistant");
+  });
+
   it("does not collapse duplicate text messages separated by another message", () => {
     const groups = messageGroups({
       messages: [

ui/src/pages/chat/chat-thread.ts

@@ -1187,7 +1187,9 @@ function buildChatItems(props: BuildChatItemsProps): Array<ChatItem | MessageGro
   const history = (Array.isArray(props.messages) ? props.messages : []).filter(
     (message) => !isAssistantHeartbeatAckForDisplay(message),
   );
-  const tools = Array.isArray(props.toolMessages) ? props.toolMessages : [];
+  const tools = Array.isArray(props.toolMessages)
+    ? props.toolMessages.filter((message) => asRecord(message) !== null)
+    : [];
   const historyKeys = buildMessageKeys(history);
   const toolKeys = buildMessageKeys(tools, history.length);
   const liftedCanvasSources = tools.flatMap((message, index) => {