Fix frontend config tests for strict type narrowing

frontend/src/components/config/__tests__/RegexList.test.tsx

@@ -26,7 +26,7 @@ describe("RegexList", () => {
       name: /Remove Test patterns pattern \d+$/i,
     });
     expect(deleteButtons).toHaveLength(2);
-    const [firstDeleteButton] = deleteButtons;
+    const firstDeleteButton = deleteButtons[0]!;
 
     fireEvent.click(firstDeleteButton);
     expect(handleChange).toHaveBeenLastCalledWith(["foo"]);

frontend/src/components/config/__tests__/StringListEditor.test.tsx

@@ -16,7 +16,8 @@ describe("StringListEditor", () => {
 
     const inputs = screen.getAllByRole("textbox");
     expect(inputs).toHaveLength(2);
-    const [firstInput, secondInput] = inputs;
+    const firstInput = inputs[0]!;
+    const secondInput = inputs[1]!;
     expect(firstInput).toHaveValue("foo");
     expect(secondInput).toHaveValue("foo");
 
@@ -36,7 +37,7 @@ describe("StringListEditor", () => {
 
     const deleteButtons = screen.getAllByRole("button", { name: /Remove entry/i });
     expect(deleteButtons).toHaveLength(3);
-    const [, secondDeleteButton] = deleteButtons;
+    const secondDeleteButton = deleteButtons[1]!;
 
     fireEvent.click(secondDeleteButton);
     expect(handleChange).toHaveBeenLastCalledWith(["one", "three"]);

frontend/src/components/config/__tests__/stableListEntries.test.ts

@@ -13,12 +13,15 @@ describe("reconcileStableStringEntries", () => {
 
     expect(next).toHaveLength(3);
     if (next.length !== 3) throw new Error("expected three entries");
+    const first = next[0]!;
+    const second = next[1]!;
+    const third = next[2]!;
 
-    expect(next[0].id).toBe("a");
+    expect(first.id).toBe("a");
-    expect(next[0].value).toBe("foo");
+    expect(first.value).toBe("foo");
-    expect(next[1].value).toBe("baz");
+    expect(second.value).toBe("baz");
-    expect(next[1].id).not.toBe("b");
+    expect(second.id).not.toBe("b");
-    expect(next[2].id).toBe("c");
+    expect(third.id).toBe("c");
   });
 
   it("reuses ids when string values move positions", () => {
@@ -31,8 +34,11 @@ describe("reconcileStableStringEntries", () => {
     const next = reconcileStableStringEntries(previous, ["bar", "foo", "baz"]);
 
     if (next.length !== 3) throw new Error("expected three entries");
-    expect(next[0].id).toBe("b");
+    const first = next[0]!;
-    expect(next[1].id).toBe("a");
+    const second = next[1]!;
-    expect(next[2].id).toBe("c");
+    const third = next[2]!;
+    expect(first.id).toBe("b");
+    expect(second.id).toBe("a");
+    expect(third.id).toBe("c");
   });
 });