fix(worker): accept omitted empty image command

experiments/perception/worker/observatory_portable/Install-Worker006AgentImage.ps1

@@ -574,7 +574,11 @@ function Assert-ImageContract {
         [string]::Join([char]0, @("python3", "-m", "k1link.observatory.m49_worker_container_main"))) {
         throw "Worker 006 installed image entrypoint changed"
     }
-    if (@($Image.Config.Cmd).Count -ne 0) {
+    $commandProperty = $Image.Config.PSObject.Properties["Cmd"]
+    if (
+        $null -ne $commandProperty -and
+        @($commandProperty.Value).Count -ne 0
+    ) {
         throw "Worker 006 installed image command changed"
     }
     if ([string]$Image.Config.User -cne "0:0") {

tests/test_worker_006_agent_image_installer.py

@@ -37,6 +37,9 @@ def test_worker_agent_installer_is_local_offline_and_non_buildkit() -> None:
         "\\\"k1link.observatory.m49_worker_container_main\\\"]'"
     ) in script
     assert 'title="NODE.DC Observatory Worker 006 agent"' not in script
+    assert '$Image.Config.PSObject.Properties["Cmd"]' in script
+    assert "$null -ne $commandProperty" in script
+    assert "@($commandProperty.Value).Count -ne 0" in script
     assert "docker rm -f $containerId" in script
     assert "docker rm -f $containerName" not in script