diff --git a/site/src/api/queries/chats.test.ts b/site/src/api/queries/chats.test.ts
index c612a047a9..d51a2909d2 100644
--- a/site/src/api/queries/chats.test.ts
+++ b/site/src/api/queries/chats.test.ts
@@ -753,3 +753,77 @@ describe("infiniteChats", () => {
 		});
 	});
 });
+
+describe("diff_status_change invalidation scope", () => {
+	// These tests verify the CORRECT invalidation pattern for
+	// diff_status_change WebSocket events. The handler should
+	// invalidate only the individual chat detail and diff-contents
+	// queries — NOT the chat list (sidebar) or messages.
+
+	it("exact chatKey invalidation does not cascade to messages or diff-contents", async () => {
+		const queryClient = createTestQueryClient();
+		const chatId = "chat-1";
+
+		// Seed all the queries that are active on the /agents/:id page.
+		queryClient.setQueryData(chatKey(chatId), makeChat(chatId));
+		queryClient.setQueryData(chatMessagesKey(chatId), []);
+		queryClient.setQueryData(chatDiffContentsKey(chatId), { files: [] });
+		queryClient.setQueryData(chatsKey, [makeChat(chatId)]);
+
+		// This is what the fixed handler does — exact: true.
+		await queryClient.invalidateQueries({
+			queryKey: chatKey(chatId),
+			exact: true,
+		});
+
+		// chatKey itself should be invalidated.
+		expect(
+			queryClient.getQueryState(chatKey(chatId))?.isInvalidated,
+			"chatKey should be invalidated",
+		).toBe(true);
+
+		// Messages should NOT be invalidated.
+		expect(
+			queryClient.getQueryState(chatMessagesKey(chatId))?.isInvalidated,
+			"chatMessagesKey should NOT be invalidated by exact chatKey",
+		).not.toBe(true);
+
+		// Diff-contents should NOT be invalidated.
+		expect(
+			queryClient.getQueryState(chatDiffContentsKey(chatId))?.isInvalidated,
+			"chatDiffContentsKey should NOT be invalidated by exact chatKey",
+		).not.toBe(true);
+
+		// Chat list should NOT be invalidated.
+		expect(
+			queryClient.getQueryState(chatsKey)?.isInvalidated,
+			"chatsKey should NOT be invalidated by exact chatKey",
+		).not.toBe(true);
+	});
+
+	it("without exact: true, chatKey invalidation cascades to messages and diff-contents (the old bug)", async () => {
+		const queryClient = createTestQueryClient();
+		const chatId = "chat-1";
+
+		queryClient.setQueryData(chatKey(chatId), makeChat(chatId));
+		queryClient.setQueryData(chatMessagesKey(chatId), []);
+		queryClient.setQueryData(chatDiffContentsKey(chatId), { files: [] });
+
+		// This is what the OLD (broken) handler did — no exact: true.
+		await queryClient.invalidateQueries({
+			queryKey: chatKey(chatId),
+		});
+
+		// Without exact: true, ALL queries starting with ["chats", chatId]
+		// get invalidated, including messages and diff-contents.
+		expect(
+			queryClient.getQueryState(chatMessagesKey(chatId))?.isInvalidated,
+			"chatMessagesKey IS invalidated without exact: true (old bug)",
+		).toBe(true);
+
+		expect(
+			queryClient.getQueryState(chatDiffContentsKey(chatId))?.isInvalidated,
+			"chatDiffContentsKey IS invalidated without exact: true (old bug)",
+		).toBe(true);
+	});
+});
diff --git a/site/src/pages/AgentsPage/AgentsPage.tsx b/site/src/pages/AgentsPage/AgentsPage.tsx
index b2676eeabb..682ed6045c 100644
--- a/site/src/pages/AgentsPage/AgentsPage.tsx
+++ b/site/src/pages/AgentsPage/AgentsPage.tsx
@@ -395,15 +395,13 @@ const AgentsPage: FC = () => {
 					}
 
 					if (chatEvent.kind === "diff_status_change") {
-						void Promise.all([
-							queryClient.invalidateQueries({
-								queryKey: chatKey(updatedChat.id),
-							}),
-							queryClient.invalidateQueries({
-								queryKey: chatDiffContentsKey(updatedChat.id),
-							}),
-							invalidateChatListQueries(queryClient),
-						]);
+						// Only refetch the diff file contents — the chat's
+						// diff_status field is already written into the
+						// chatKey and infinite-list caches below.
+						void queryClient.invalidateQueries({
+							queryKey: chatDiffContentsKey(updatedChat.id),
+							exact: true,
+						});
 					}
 					// Scope field updates by event kind so that
 					// status_change events (which may carry a stale title