Make ingress drill Docker socket portable

docs/INSTALLATION_AND_DEPLOYMENT_ARCHITECTURE.md

@@ -162,6 +162,9 @@ Ingress acceptance streams generated configuration into Docker-managed
 volumes before starting the read-only containers. It therefore also works when
 an Actions job reaches a host or remote Docker daemon through a mounted socket;
 the drill never assumes that a job-container path is visible to that daemon.
+The bounded setup helper writes only generated public configuration as root so
+it can initialize a new volume; the actual HAProxy process retains the image's
+non-root identity and runs read-only with all capabilities dropped.
 
 The manifest contract is
 [`runtime-distribution-manifest.schema.json`](runtime-distribution-manifest.schema.json),

tests/test_managed_ingress_drill.py

@@ -37,6 +37,7 @@ class ManagedIngressDrillTests(unittest.TestCase):
 
         argv = run.call_args.args[0]
         self.assertIn("type=volume,src=config-volume,dst=/govoplan-config", argv)
+        self.assertIn("0:0", argv)
         self.assertNotIn("type=bind", " ".join(argv))
         self.assertEqual(
             ":8080 { respond /health 200 }\n",

tools/checks/managed-ingress-drill.py

@@ -64,6 +64,8 @@ def _write_volume_file(
             "run",
             "--rm",
             "--interactive",
+            "--user",
+            "0:0",
             "--mount",
             f"type=volume,src={volume},dst=/govoplan-config",
             "--entrypoint",