fix(KB-217): resolve planning mode hanging race condition

- Fix race condition causing planning mode to hang after submitting answers
- Keep SSE connection alive during response submission to prevent premature disconnect
- Add scrollable CSS styling for AI thinking output display in planning mode
- Add tests for race condition fix ensuring subsequent questions are received
- Include changeset for planning mode patch release

packages/dashboard/app/components/PlanningModeModal.test.tsx

@@ -302,6 +302,78 @@ describe("PlanningModeModal", () => {
       expect(container.querySelector(".planning-question-form > .planning-view-scroll")).not.toBeNull();
       expect(container.querySelector(".planning-question-form > .planning-actions")).not.toBeNull();
     });
+
+    it("receives second question after answering first without hanging (race condition fix)", async () => {
+      const secondQuestion: PlanningQuestion = {
+        id: "q-requirements",
+        type: "text",
+        question: "What are the key requirements?",
+        description: "Describe the requirements",
+      };
+
+      // Track how many times connectPlanningStream is called
+      let streamConnectionCount = 0;
+      let streamHandlers: any = null;
+
+      mockConnectPlanningStream.mockImplementation((sessionId: string, handlers: any) => {
+        streamConnectionCount++;
+        streamHandlers = handlers;
+        
+        // Only send first question on initial connection
+        if (streamConnectionCount === 1) {
+          setTimeout(() => {
+            handlers.onQuestion?.(mockQuestion);
+          }, 10);
+        }
+        
+        return {
+          close: vi.fn(),
+          isConnected: vi.fn().mockReturnValue(true),
+        };
+      });
+
+      mockRespondToPlanning.mockImplementation(async () => {
+        // Simulate server broadcasting second question via the existing SSE connection
+        // This should use the same handlers from the initial connection
+        setTimeout(() => {
+          if (streamHandlers) {
+            streamHandlers.onQuestion?.(secondQuestion);
+          }
+        }, 5);
+        return { sessionId: "session-123", currentQuestion: null, summary: null };
+      });
+
+      render(
+        <PlanningModeModal
+          isOpen={true}
+          onClose={mockOnClose}
+          onTaskCreated={mockOnTaskCreated}
+          tasks={mockTasks}
+        />
+      );
+
+      const textarea = screen.getByPlaceholderText(/e.g., Build a user authentication/);
+      fireEvent.change(textarea, { target: { value: "Build auth system" } });
+      fireEvent.click(screen.getByText("Start Planning"));
+
+      // Wait for first question
+      await waitFor(() => {
+        expect(screen.getByText("What is the scope?")).toBeDefined();
+      });
+
+      // Answer the first question
+      fireEvent.click(screen.getByText("Medium"));
+      fireEvent.click(screen.getByText("Continue"));
+
+      // Wait for second question to appear (should NOT hang)
+      await waitFor(() => {
+        expect(screen.getByText("What are the key requirements?")).toBeDefined();
+      }, { timeout: 3000 });
+
+      // Verify SSE connection was established only ONCE (not reconnected)
+      // This confirms the race condition fix - the same connection is reused
+      expect(streamConnectionCount).toBe(1);
+    });
   });
 
   describe("Summary view", () => {

packages/dashboard/app/components/PlanningModeModal.tsx

@@ -237,57 +237,21 @@ export function PlanningModeModal({ isOpen, onClose, onTaskCreated, tasks, initi
       const { session } = view;
       const sessionId = session.sessionId;
       setError(null);
-      setStreamingOutput("");
+
+      // Keep the existing SSE connection alive - do NOT close it!
+      // The connection established in handleStartPlanning will continue
+      // to receive events (thinking, question, summary) throughout the session.
+      // This prevents the race condition where events are missed because
+      // the frontend disconnects and reconnects after the API call.
+
       setView({ type: "loading" });
+      setStreamingOutput(""); // Clear old thinking output when entering loading state
 
       try {
-        // Close previous connection if any
-        streamConnectionRef.current?.close();
-
-        // Submit response - this will trigger the AI to process and stream
-        const updatedSession = await respondToPlanning(sessionId, responses);
+        // Submit response - AI will broadcast events via the already-connected stream
+        await respondToPlanning(sessionId, responses);
         setResponseHistory((prev) => [...prev, responses]);
-
-        // If we got an immediate response (non-streaming mode), use it
-        if (updatedSession.summary) {
-          setView({ type: "summary", session: updatedSession, summary: updatedSession.summary });
-          setEditedSummary(updatedSession.summary);
-          return;
-        }
-        if (updatedSession.currentQuestion) {
-          setView({ type: "question", session: updatedSession });
-          return;
-        }
-
-        // Otherwise, set up streaming for the next question
-        const connection = connectPlanningStream(sessionId, {
-          onThinking: (data) => {
-            setStreamingOutput((prev) => prev + data);
-          },
-          onQuestion: (question) => {
-            setView({
-              type: "question",
-              session: { sessionId, currentQuestion: question, summary: null },
-            });
-            setStreamingOutput("");
-          },
-          onSummary: (summary) => {
-            setView({
-              type: "summary",
-              session: { sessionId, currentQuestion: null, summary },
-              summary,
-            });
-            setEditedSummary(summary);
-            setStreamingOutput("");
-          },
-          onError: (message) => {
-            setError(message);
-            setView({ type: "question", session });
-            setStreamingOutput("");
-          },
-        });
-
-        streamConnectionRef.current = connection;
+        // Events (question/summary) will arrive via the existing SSE stream
       } catch (err: any) {
         setError(err.message || "Failed to submit response");
         setView({ type: "question", session });

packages/dashboard/app/styles.css

@@ -6918,6 +6918,56 @@ html .column.drag-over * {
   color: var(--text-muted);
 }
 
+/* AI Thinking Output Display */
+.planning-thinking-container {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 12px;
+  width: 100%;
+  max-width: 600px;
+}
+
+.planning-thinking-toggle {
+  padding: 6px 12px;
+  font-size: 13px;
+  font-weight: 500;
+  color: var(--text-muted);
+  background: var(--card);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-md);
+  cursor: pointer;
+  transition: all 0.15s ease;
+}
+
+.planning-thinking-toggle:hover {
+  background: var(--card-hover);
+  color: var(--text);
+}
+
+.planning-thinking-output {
+  width: 100%;
+  max-height: 300px;
+  overflow-y: auto;
+  overflow-x: hidden;
+  background: var(--card);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-lg);
+  padding: 16px;
+  text-align: left;
+}
+
+.planning-thinking-output pre {
+  margin: 0;
+  white-space: pre-wrap;
+  word-wrap: break-word;
+  overflow-wrap: break-word;
+  font-family: var(--font-mono);
+  font-size: 13px;
+  line-height: 1.6;
+  color: var(--text);
+}
+
 /* Responsive */
 @media (max-width: 768px) {
   .planning-modal {
@@ -6996,6 +7046,20 @@ html .column.drag-over * {
     max-width: none;
   }
 
+  /* Planning thinking output mobile adjustments */
+  .planning-thinking-container {
+    max-width: 100%;
+  }
+
+  .planning-thinking-output {
+    max-height: 200px;
+    padding: 12px;
+  }
+
+  .planning-thinking-output pre {
+    font-size: 12px;
+  }
+
   /* Prevent mobile zoom on focus for planning text inputs (16px minimum) */
   .planning-textarea {
     font-size: 16px;