NOTE: The verifier rejected this jsdom class-contract patch.
The revised reproduction uses the saved 362-by-390 browser layout test instead:
PluginPendingInteractionComposer.mobile-layout.repro.test.tsx

diff --git a/apps/app/src/components/plugin/PluginPendingInteractionComposer.test.tsx b/apps/app/src/components/plugin/PluginPendingInteractionComposer.test.tsx
index cacfdc1c7..1762b7f1c 100644
--- a/apps/app/src/components/plugin/PluginPendingInteractionComposer.test.tsx
+++ b/apps/app/src/components/plugin/PluginPendingInteractionComposer.test.tsx
@@ -69,6 +69,32 @@ afterEach(() => {
 });
 
 describe("PluginPendingInteractionComposer", () => {
+  it("removes the fieldset from plugin form layout", () => {
+    function WideRenderer() {
+      return <div data-testid="wide-renderer">wide renderer</div>;
+    }
+    setPluginSlotRegistrations(
+      "secrets",
+      registrations([{ id: "secret-request", component: WideRenderer }]),
+    );
+
+    renderComposer(
+      <PluginPendingInteractionComposer
+        interaction={interaction}
+        request={{
+          pluginId: "secrets",
+          rendererId: "secret-request",
+          title: interaction.payload.title,
+          data: interaction.payload.data,
+        }}
+        dismissal="cancel"
+      />,
+    );
+
+    const fieldset = screen.getByTestId("wide-renderer").closest("fieldset");
+    expect(fieldset?.classList.contains("contents")).toBe(true);
+  });
+
   it("mounts only the renderer registered by the interaction's plugin", () => {
     function WrongRenderer() {
       return <div>wrong plugin renderer</div>;