fix(gui): don't drop batched messages after a <think> block

gui/src/redux/slices/sessionSlice.test.ts

@@ -133,6 +133,45 @@ describe("sessionSlice streamUpdate", () => {
       );
       expect(newState.history[1].message.id).toBe("mock-uuid-1");
     });
+
+    it("should not drop later messages in a batch after a <think> block", () => {
+      const initialState = createInitialState();
+      // Mirror the production layout: submitEditorAndInitAtIndex appends an
+      // empty assistant placeholder after the user message, so reasoning is
+      // attached to that placeholder rather than to the user turn.
+      initialState.history.push({
+        message: {
+          role: "assistant" as const,
+          content: "",
+          id: "initial-assistant-message",
+        },
+        contextItems: [],
+      });
+
+      const action = {
+        type: "session/streamUpdate",
+        payload: [
+          {
+            role: "assistant" as const,
+            content: "<think>Reasoning here.</think>First part.",
+          },
+          {
+            role: "assistant" as const,
+            content: " Second part.",
+          },
+        ],
+      };
+
+      const newState = sessionSlice.reducer(initialState, action);
+
+      expect(newState.history[1].message.role).toBe("assistant");
+      expect(newState.history[1].reasoning?.text).toBe("Reasoning here.");
+
+      // The second message in the same payload must still be appended.
+      expect(newState.history[2].message.content).toBe(
+        "First part. Second part.",
+      );
+    });
   });
 
   describe("Tool Call With Response", () => {

gui/src/redux/slices/sessionSlice.ts

@@ -580,7 +580,11 @@ export const sessionSlice = createSlice({
 
               handleToolCallsInMessage(message, lastItem);
 
-              return;
+              // `continue`, not `return`: this branch has finished handling
+              // *this* message, but `action.payload` may contain more. A
+              // `return` here exits the reducer entirely and silently drops
+              // every remaining message in the batch.
+              continue;
             }
           }