🤖 fix: narrow mux message type guard for mobile

Change-Id: I89207a670656a722fbcfed3cdf4057db195c85b3
Signed-off-by: Test <test@example.com>

Author: Test

mobile/src/messages/normalizeChatEvent.ts

@@ -279,32 +279,35 @@ export function createChatEventExpander(): ChatEventExpander {
       return payload.flatMap((item) => expandSingle(item));
     }
 
-    if (isObject(payload) && isMuxMessage(payload as WorkspaceChatMessage)) {
-      const muxMessage = payload as MuxMessage;
-      const historySequence = muxMessage.metadata?.historySequence;
-
-      if (typeof historySequence !== "number" || !Number.isFinite(historySequence)) {
-        console.warn(`${DEBUG_TAG} Dropping mux message without historySequence`, {
-          id: muxMessage.id,
-          role: muxMessage.role,
-          metadata: muxMessage.metadata,
-        });
-        return [];
-      }
+    if (isObject(payload)) {
+      const candidate = payload as WorkspaceChatMessage;
+      if (isMuxMessage(candidate)) {
+        const muxMessage: MuxMessage = candidate;
+        const historySequence = muxMessage.metadata?.historySequence;
+
+        if (typeof historySequence !== "number" || !Number.isFinite(historySequence)) {
+          console.warn(`${DEBUG_TAG} Dropping mux message without historySequence`, {
+            id: muxMessage.id,
+            role: muxMessage.role,
+            metadata: muxMessage.metadata,
+          });
+          return [];
+        }
 
-      processor.handleEvent(muxMessage as WorkspaceChatMessage);
-      const displayed = transformMuxToDisplayed(muxMessage);
+        processor.handleEvent(muxMessage as WorkspaceChatMessage);
+        const displayed = transformMuxToDisplayed(muxMessage);
 
-      if (displayed.length === 0) {
-        debugLog("Mux message yielded no displayable entries", {
-          id: muxMessage.id,
-          role: muxMessage.role,
-          historySequence,
-        });
-        return [];
-      }
+        if (displayed.length === 0) {
+          debugLog("Mux message yielded no displayable entries", {
+            id: muxMessage.id,
+            role: muxMessage.role,
+            historySequence,
+          });
+          return [];
+        }
 
-      return displayed;
+        return displayed;
+      }
     }
     if (typeof payload === "string" || typeof payload === "number") {
       // Skip primitive values - they're not valid events