fix: urls.primaryName functionality regression (via #5097)

* add tests

* compute index before triggering URL load

* bonus: improve urls topbar label

test/e2e-cypress/tests/features/urls.js

@@ -0,0 +1,38 @@
+describe("configuration options: `urls` and `urls.primaryName`", () => {
+  describe("`urls` only", () => {
+    it("should render a list of URLs correctly", () => {
+      cy.visit("/?configUrl=/configs/urls.yaml")
+        .get("select")
+        .children()
+        .should("have.length", 2)
+        .get("select > option")
+        .eq(0)
+        .should("have.text", "One")
+        .should("have.attr", "value", "/documents/features/urls/1.yaml")
+        .get("select > option")
+        .eq(1)
+        .should("have.text", "Two")
+        .should("have.attr", "value", "/documents/features/urls/2.yaml")
+    })
+
+    it("should render the first URL in the list", () => {
+      cy.visit("/?configUrl=/configs/urls.yaml")
+        .get("h2.title")
+        .should("have.text", "One")
+        .window()
+        .then(win => win.ui.specSelectors.url())
+        .should("equal", "/documents/features/urls/1.yaml")
+    })
+  })
+
+  it("should respect a `urls.primaryName`", () => {
+    cy.visit("/?configUrl=/configs/urls-primary-name.yaml")
+      .get("select")
+      .should("have.value", "/documents/features/urls/2.yaml")
+      .get("h2.title")
+      .should("have.text", "Two")
+      .window()
+      .then(win => win.ui.specSelectors.url())
+      .should("equal", "/documents/features/urls/2.yaml")
+  })
+})