fix(seer-explorer): Prevent optimistic state clearing on rethink with ame message (#111721)

+ When a user rethinks and re-sends the same message, the clearing
effect was matching stale pre-truncation server blocks, causing deleted
blocks to briefly reappear and the thinking indicator to vanish. Store
the session updated_at as a baseline when setting optimistic state and
skip the clearing effect until the server has actually processed the
request.
+ Was introduced when fixing another bug in this PR:
#111685

Co-authored-by: Claude Sonnet 4 <noreply@anthropic.com>

Author: Mihir-Mavalankar

static/app/views/seerExplorer/hooks/useSeerExplorer.spec.tsx

@@ -222,5 +222,55 @@ describe('useSeerExplorer', () => {
       const blocks = result.current.sessionData?.blocks ?? [];
       expect(blocks.some(b => b.message.role === 'assistant' && b.loading)).toBe(true);
     });
+
+    it('keeps optimistic state when rethinking with the same message', async () => {
+      const chatUrl = `/organizations/${organization.slug}/seer/explorer-chat/`;
+      const ts = '2024-01-01T00:00:00Z';
+
+      MockApiClient.addMockResponse({url: chatUrl, method: 'GET', body: {session: null}});
+      MockApiClient.addMockResponse({
+        url: `${chatUrl}789/`,
+        method: 'GET',
+        body: {
+          session: {
+            blocks: [
+              {
+                id: 'u0',
+                message: {role: 'user', content: 'hello'},
+                timestamp: ts,
+                loading: false,
+              },
+              {
+                id: 'a1',
+                message: {role: 'assistant', content: 'Hi!'},
+                timestamp: ts,
+                loading: false,
+              },
+            ],
+            run_id: 789,
+            status: 'completed',
+            updated_at: ts,
+          },
+        },
+      });
+      MockApiClient.addMockResponse({
+        url: `${chatUrl}789/`,
+        method: 'POST',
+        body: {run_id: 789},
+      });
+
+      const {result} = renderHookWithProviders(() => useSeerExplorer(), {organization});
+
+      act(() => result.current.switchToRun(789));
+      await waitFor(() => result.current.sessionData?.blocks?.length === 2);
+
+      act(() => result.current.deleteFromIndex(0));
+      await act(async () => {
+        await result.current.sendMessage('hello');
+      });
+
+      expect(result.current.sessionData?.blocks?.some(b => b.loading)).toBe(true);
+      expect(result.current.deletedFromIndex).toBe(0);
+    });
   });
 });

static/app/views/seerExplorer/hooks/useSeerExplorer.tsx

@@ -148,6 +148,7 @@ export const useSeerExplorer = () => {
   const [optimistic, setOptimistic] = useState<{
     assistantBlockId: string;
     assistantContent: string;
+    baselineUpdatedAt: string | undefined;
     insertIndex: number;
     userBlockId: string;
     userQuery: string;
@@ -231,6 +232,7 @@ export const useSeerExplorer = () => {
           calculatedInsertIndex + 1
         ),
         assistantContent: assistantContent || 'Thinking...',
+        baselineUpdatedAt: apiData?.session?.updated_at,
       });
 
       try {
@@ -450,6 +452,10 @@ export const useSeerExplorer = () => {
       return undefined;
     }
 
+    if (apiData?.session?.updated_at === optimistic.baselineUpdatedAt) {
+      return undefined;
+    }
+
     const serverBlocks = apiData?.session?.blocks || [];
     const blockAtInsert = serverBlocks[optimistic.insertIndex];
 
@@ -471,7 +477,7 @@ export const useSeerExplorer = () => {
     }
 
     return undefined;
-  }, [apiData?.session?.blocks, optimistic]);
+  }, [apiData?.session?.blocks, apiData?.session?.updated_at, optimistic]);
 
   // Detect PR creation errors and show error messages
   useEffect(() => {