fix(webui): handle final stream image rewrites

webui/src/hooks/useNanobotStream.ts

@@ -520,15 +520,28 @@ export function useNanobotStream(
           resolveActiveAssistantIndex(next)
           ?? findStreamingAssistantIndex(next, closedAssistantStreamIdsRef.current)
           ?? findLatestAssistantAnswerIndex(next);
-        if (targetIndex !== null) {
-          const target = next[targetIndex];
-          next = replaceMessageAt(next, targetIndex, {
-            ...target,
-            content: finalAnswerText,
-            isStreaming: true,
-          });
+          if (targetIndex !== null) {
+            const target = next[targetIndex];
+            next = replaceMessageAt(next, targetIndex, {
+              ...target,
+              content: finalAnswerText,
+              isStreaming: true,
+            });
+          } else {
+            const id = crypto.randomUUID();
+            closedAssistantStreamIdsRef.current.add(id);
+            next = [
+              ...next,
+              {
+                id,
+                role: "assistant",
+                content: finalAnswerText,
+                isStreaming: true,
+                createdAt: Date.now(),
+              },
+            ];
+          }
         }
-      }
       if (options?.closeAnswerSegment) closeActiveAssistantStream();
       return next;
     });

webui/src/tests/useNanobotStream.test.tsx

@@ -1298,6 +1298,28 @@ describe("useNanobotStream", () => {
     });
   });
 
+  it("creates an assistant bubble from final stream_end text without prior delta", () => {
+    const fake = fakeClient();
+    const { result } = renderHook(() => useNanobotStream("chat-stream-end-only", EMPTY_MESSAGES), {
+      wrapper: wrap(fake.client),
+    });
+
+    act(() => {
+      fake.emit("chat-stream-end-only", {
+        event: "stream_end",
+        chat_id: "chat-stream-end-only",
+        text: "![Diagram](/api/media/sig/payload)",
+      });
+    });
+
+    expect(result.current.messages).toHaveLength(1);
+    expect(result.current.messages[0]).toMatchObject({
+      role: "assistant",
+      content: "![Diagram](/api/media/sig/payload)",
+      isStreaming: true,
+    });
+  });
+
   it("stamps latency on the last assistant bubble from turn_end", () => {
     const fake = fakeClient();
     const { result } = renderHook(() => useNanobotStream("chat-lat", EMPTY_MESSAGES), {