Add e2e test for /system/standby endpoints

Spins up the headless image via testcontainers and exercises:
- Idempotent disable (two consecutive 204s)
- A normal request flows while pinned (middleware coexistence)
- Idempotent enable (two consecutive 204s)

The unikraft control file does not exist inside the docker test
container, so the underlying scale-to-zero write is a no-op. The
test validates HTTP wiring and handler/middleware coexistence; the
deep pin semantics are covered by unit tests against DebouncedController.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: sjmiller609

server/e2e/e2e_standby_test.go

@@ -0,0 +1,60 @@
+package e2e
+
+import (
+	"context"
+	"net/http"
+	"os/exec"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+// TestStandbyDisableEnable exercises POST /system/standby/{disable,enable}
+// against the real built image. The unikraft control file does not exist
+// inside the docker test container, so the underlying scale-to-zero write
+// is a no-op — this test validates HTTP wiring, idempotency, and that the
+// scale-to-zero middleware coexists with the pin handlers.
+func TestStandbyDisableEnable(t *testing.T) {
+	t.Parallel()
+
+	if _, err := exec.LookPath("docker"); err != nil {
+		t.Skipf("docker not available: %v", err)
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Minute)
+	defer cancel()
+
+	c := NewTestContainer(t, headlessImage)
+	require.NoError(t, c.Start(ctx, ContainerConfig{}), "failed to start container")
+	defer c.Stop(ctx)
+
+	require.NoError(t, c.WaitReady(ctx), "api not ready")
+
+	client, err := c.APIClient()
+	require.NoError(t, err, "failed to create API client")
+
+	// Idempotent disable.
+	r1, err := client.DisableStandbyWithResponse(ctx)
+	require.NoError(t, err, "DisableStandby request failed")
+	require.Equal(t, http.StatusNoContent, r1.StatusCode(), "unexpected status: %s body=%s", r1.Status(), string(r1.Body))
+
+	r2, err := client.DisableStandbyWithResponse(ctx)
+	require.NoError(t, err, "second DisableStandby request failed")
+	require.Equal(t, http.StatusNoContent, r2.StatusCode(), "unexpected status: %s body=%s", r2.Status(), string(r2.Body))
+
+	// Normal request must still flow while pinned (scaletozero middleware
+	// runs on every request — the pin must not deadlock or break it).
+	readResp, err := client.ReadClipboardWithResponse(ctx)
+	require.NoError(t, err, "ReadClipboard request failed while pinned")
+	require.Equal(t, http.StatusOK, readResp.StatusCode(), "unexpected read status while pinned: %s body=%s", readResp.Status(), string(readResp.Body))
+
+	// Idempotent enable.
+	r3, err := client.EnableStandbyWithResponse(ctx)
+	require.NoError(t, err, "EnableStandby request failed")
+	require.Equal(t, http.StatusNoContent, r3.StatusCode(), "unexpected status: %s body=%s", r3.Status(), string(r3.Body))
+
+	r4, err := client.EnableStandbyWithResponse(ctx)
+	require.NoError(t, err, "second EnableStandby request failed")
+	require.Equal(t, http.StatusNoContent, r4.StatusCode(), "unexpected status: %s body=%s", r4.Status(), string(r4.Body))
+}