fix(ui): persist budget window deletion on virtual keys (#31107)

Deleting every budget window from a virtual key looked like it saved but
reverted on reload, while editing a window persisted. The key edit form set
budget_limits to undefined once the window list was emptied, and
JSON.stringify drops undefined keys, so /key/update received no budget_limits
field at all and model_dump(exclude_unset=True) skipped the existing
clear-on-empty branch. Sending [] instead lets the backend store JSON null and
clear the stored windows, matching how it already treats an explicit empty list

Resolves LIT-3742

ui/litellm-dashboard/src/components/templates/key_edit_view.test.tsx

@@ -600,6 +600,96 @@ describe("KeyEditView", () => {
     });
   });
 
+  it("should submit budget_limits: [] when the last budget window is deleted", async () => {
+    const onSubmitMock = vi.fn().mockResolvedValue(undefined);
+    const keyDataWithWindow = {
+      ...MOCK_KEY_DATA,
+      budget_limits: [{ budget_duration: "30d", max_budget: 100 }],
+    };
+    renderWithProviders(
+      <KeyEditView
+        keyData={keyDataWithWindow}
+        onCancel={() => {}}
+        onSubmit={onSubmitMock}
+        accessToken={"test-token"}
+        userID={"test-user"}
+        userRole={"admin"}
+        premiumUser={false}
+      />,
+    );
+
+    const deleteWindowButton = await screen.findByRole("button", { name: "✕" });
+    await userEvent.click(deleteWindowButton);
+
+    const submitButton = screen.getByRole("button", { name: /save changes/i });
+    await userEvent.click(submitButton);
+
+    await waitFor(() => {
+      expect(onSubmitMock).toHaveBeenCalled();
+      const callArgs = onSubmitMock.mock.calls[0][0];
+      expect(callArgs.budget_limits).toEqual([]);
+    });
+  });
+
+  it("should resend existing budget windows on submit when they are left untouched", async () => {
+    const onSubmitMock = vi.fn().mockResolvedValue(undefined);
+    const keyDataWithWindow = {
+      ...MOCK_KEY_DATA,
+      budget_limits: [{ budget_duration: "30d", max_budget: 100 }],
+    };
+    renderWithProviders(
+      <KeyEditView
+        keyData={keyDataWithWindow}
+        onCancel={() => {}}
+        onSubmit={onSubmitMock}
+        accessToken={"test-token"}
+        userID={"test-user"}
+        userRole={"admin"}
+        premiumUser={false}
+      />,
+    );
+
+    const submitButton = await screen.findByRole("button", { name: /save changes/i });
+    await userEvent.click(submitButton);
+
+    await waitFor(() => {
+      expect(onSubmitMock).toHaveBeenCalled();
+      const callArgs = onSubmitMock.mock.calls[0][0];
+      expect(callArgs.budget_limits).toEqual([{ budget_duration: "30d", max_budget: 100 }]);
+    });
+  });
+
+  it("should omit budget_limits (not clear stored windows) when a window is left incomplete", async () => {
+    const onSubmitMock = vi.fn().mockResolvedValue(undefined);
+    const keyDataWithWindow = {
+      ...MOCK_KEY_DATA,
+      budget_limits: [{ budget_duration: "30d", max_budget: 100 }],
+    };
+    renderWithProviders(
+      <KeyEditView
+        keyData={keyDataWithWindow}
+        onCancel={() => {}}
+        onSubmit={onSubmitMock}
+        accessToken={"test-token"}
+        userID={"test-user"}
+        userRole={"admin"}
+        premiumUser={false}
+      />,
+    );
+
+    const maxBudgetInput = await screen.findByPlaceholderText("Max spend ($)");
+    await userEvent.clear(maxBudgetInput);
+
+    const submitButton = screen.getByRole("button", { name: /save changes/i });
+    await userEvent.click(submitButton);
+
+    await waitFor(() => {
+      expect(onSubmitMock).toHaveBeenCalled();
+      const callArgs = onSubmitMock.mock.calls[0][0];
+      expect(callArgs.budget_limits).toBeUndefined();
+    });
+  });
+
   it("should display 'AI APIs' label for the llm_api key type option", async () => {
     const keyDataWithLlmApiRoutes = {
       ...MOCK_KEY_DATA,

ui/litellm-dashboard/src/components/templates/key_edit_view.tsx

@@ -290,11 +290,19 @@ export function KeyEditView({
         values.duration = null;
       }
 
-      // Include multi-window budget limits (filter out incomplete entries)
+      // Reconcile multi-window budget limits from the editor state, dropping
+      // incomplete entries (no max_budget). Sending [] tells the backend to clear
+      // all stored windows, so only send it when the user removed every window;
+      // when entries remain but are still incomplete, omit the field so the saved
+      // windows are left untouched (JSON.stringify drops the undefined key).
       const validWindows = budgetLimits.filter(
         (w) => w.budget_duration && w.max_budget !== null && w.max_budget !== undefined,
       );
-      values.budget_limits = validWindows.length > 0 ? validWindows : undefined;
+      if (validWindows.length > 0) {
+        values.budget_limits = validWindows;
+      } else if (budgetLimits.length === 0) {
+        values.budget_limits = [];
+      }
 
       await onSubmit(values);
     } finally {