fix(ui): avoid nested activity main landmark (#127789)

Co-authored-by: Amp <amp@ampcode.com>

ui/src/pages/activity/session-activity-view.test.ts

@@ -46,6 +46,21 @@ function props(overrides: Partial<Parameters<typeof renderSessionActivityView>[0
   };
 }
 
+describe("session activity semantics", () => {
+  beforeEach(() => {
+    document.body.innerHTML = "";
+  });
+
+  it("leaves the page main landmark to the app shell", () => {
+    const container = document.createElement("div");
+    document.body.append(container);
+
+    render(renderSessionActivityView(props()), container);
+
+    expect(container.querySelectorAll("main")).toHaveLength(0);
+  });
+});
+
 describe("session activity people filter", () => {
   beforeEach(() => {
     document.body.innerHTML = "";

ui/src/pages/activity/session-activity-view.ts

@@ -458,7 +458,7 @@ export function renderSessionActivityView(props: SessionActivityViewProps) {
         </div>
         ${renderPeopleControl(props, people, selectedPerson, projection.timeCount)}
       </div>
-      <main class="activity-feed__main">
+      <div class="activity-feed__main">
         ${props.filters.personId
           ? identity
             ? renderIdentityHeader(props.context, identity, props.rows)
@@ -490,7 +490,7 @@ export function renderSessionActivityView(props: SessionActivityViewProps) {
                   </section>`}
             `
           : nothing}
-      </main>
+      </div>
     </div>
   `;
 }