diff --git a/backend/tests/test_delivery.py b/backend/tests/test_delivery.py
index 333a337..24995c9 100644
--- a/backend/tests/test_delivery.py
+++ b/backend/tests/test_delivery.py
@@ -5,9 +5,11 @@ import json
 import os
 import secrets
 import stat
+import subprocess
 import sys
 from contextlib import nullcontext
 from pathlib import Path
+from types import SimpleNamespace
 from uuid import UUID
 
 import pytest
@@ -43,6 +45,47 @@ node_observation = importlib.import_module("scripts.release.node_observation")
 installer = importlib.import_module("scripts.release.install")
 
 
+@pytest.mark.parametrize("mode,owner", [(stat.S_IFREG, 0), (stat.S_IFSOCK, 1000)])
+def test_system_bus_preflight_refuses_unprotected_endpoint(monkeypatch, mode, owner):
+    monkeypatch.setattr(installer.preflight, "protected", lambda *args, **kwargs: None)
+    monkeypatch.setattr(Path, "lstat", lambda _: SimpleNamespace(st_mode=mode, st_uid=owner))
+    with pytest.raises(policy.DeliveryError, match="socket absent/unprotected"):
+        installer.preflight.system_bus()
+
+
+@pytest.mark.parametrize(
+    "response", [(0, 's "262"\n'), (0, 's "262-1-arch"\n'), (1, ""), (0, 's "other"\n')]
+)
+def test_system_bus_preflight_requires_bounded_manager_response(monkeypatch, response):
+    monkeypatch.setattr(installer.preflight, "protected", lambda *args, **kwargs: None)
+    monkeypatch.setattr(Path, "lstat", lambda _: SimpleNamespace(st_mode=stat.S_IFSOCK, st_uid=0))
+
+    def run(args, **options):
+        assert options["timeout"] == 5 and "--timeout=3" in args
+        assert options["env"] == {"PATH": "/usr/bin", "LC_ALL": "C"}
+        return SimpleNamespace(returncode=response[0], stdout=response[1], stderr="private detail")
+
+    monkeypatch.setattr(installer.preflight.subprocess, "run", run)
+    if response[0] == 0 and response[1].startswith('s "262'):
+        assert installer.preflight.system_bus()["manager_reachable"]
+    else:
+        with pytest.raises(policy.DeliveryError, match="manager unavailable/incompatible") as error:
+            installer.preflight.system_bus()
+        assert "private detail" not in str(error.value)
+
+
+def test_system_bus_timeout_is_an_explicit_preflight_refusal(monkeypatch):
+    monkeypatch.setattr(installer.preflight, "protected", lambda *args, **kwargs: None)
+    monkeypatch.setattr(Path, "lstat", lambda _: SimpleNamespace(st_mode=stat.S_IFSOCK, st_uid=0))
+
+    def run(args, **options):
+        raise subprocess.TimeoutExpired(args, options["timeout"])
+
+    monkeypatch.setattr(installer.preflight.subprocess, "run", run)
+    with pytest.raises(policy.DeliveryError, match="system message bus unavailable"):
+        installer.preflight.system_bus()
+
+
 @pytest.mark.parametrize("mode", [0o700, 0o755, 0o555])
 def test_new_layout_directory_has_explicit_mode_under_private_umask(tmp_path, monkeypatch, mode):
     # Ordinary owned temporary files verify the umask regression. Root ownership
diff --git a/scripts/release/preflight.py b/scripts/release/preflight.py
index 6c6900e..22f078d 100644
--- a/scripts/release/preflight.py
+++ b/scripts/release/preflight.py
@@ -120,6 +120,40 @@ def identity_conflicts() -> list[str]:
     return errors
 
 
+def system_bus() -> dict:
+    """Transient bounded operator units need the actual system message bus."""
+    try:
+        endpoint = Path("/run/dbus/system_bus_socket")
+        protected(endpoint.parent, directory=True)
+        info = endpoint.lstat()
+        if not stat.S_ISSOCK(info.st_mode) or info.st_uid != 0:
+            raise DeliveryError("system message bus socket absent/unprotected")
+        protected(Path("/usr/bin/busctl"))
+        result = subprocess.run(
+            [
+                "/usr/bin/busctl",
+                "--system",
+                "--timeout=3",
+                "get-property",
+                "org.freedesktop.systemd1",
+                "/org/freedesktop/systemd1",
+                "org.freedesktop.systemd1.Manager",
+                "Version",
+            ],
+            capture_output=True,
+            text=True,
+            timeout=5,
+            env={"PATH": "/usr/bin", "LC_ALL": "C"},
+        )
+        if result.returncode or not re.fullmatch(
+            r's "262(?:[-+ .][A-Za-z0-9.+() -]{1,120})?"\n?', result.stdout
+        ):
+            raise DeliveryError("system message bus manager unavailable/incompatible")
+        return {"manager_reachable": True, "version": result.stdout.strip()}
+    except (OSError, subprocess.SubprocessError) as error:
+        raise DeliveryError("system message bus unavailable") from error
+
+
 def observe(payload: Path, *, bundle_data: dict, require_root: bool = True) -> dict:
     errors = []
     observations = {}
@@ -135,6 +169,10 @@ def observe(payload: Path, *, bundle_data: dict, require_root: bool = True) -> d
         errors.append("unsupported distribution profile")
     if Path("/proc/1/comm").read_text().strip() != "systemd":
         errors.append("systemd PID1 required")
+    try:
+        observations["system_bus"] = system_bus()
+    except DeliveryError as error:
+        errors.append(str(error))
     try:
         observations["hardware"] = hardware()
         flags = set(observations["hardware"]["processor"].get("flags", "").split())
@@ -258,7 +296,7 @@ def observe(payload: Path, *, bundle_data: dict, require_root: bool = True) -> d
             protected(Path(directory), directory=True)
         except (OSError, DeliveryError):
             errors.append("installation ancestor unprotected")
-    # No socket is opened for a running service and no peer is contacted.
+    # Port occupation checks do not connect to application peers.
     for port in (8000, 8100):
         with socket.socket() as check:
             try: