diff --git a/PUBLIC_SOURCE_EXPORT.md b/PUBLIC_SOURCE_EXPORT.md
index 51919e9..674102f 100644
--- a/PUBLIC_SOURCE_EXPORT.md
+++ b/PUBLIC_SOURCE_EXPORT.md
@@ -1,3 +1,3 @@
 # Public source export
 
-This source snapshot was generated from the private canonical repository at revision `87aa7dda6889fd951d202754d76daaaa1e98e26b`. It contains no private Git history or operational evidence. Changes are published from the canonical repository.
+This source snapshot was generated from the private canonical repository at revision `166e10b7084c977816a75560d015da8f350c534c`. It contains no private Git history or operational evidence. Changes are published from the canonical repository.
diff --git a/PUBLIC_SOURCE_MANIFEST.json b/PUBLIC_SOURCE_MANIFEST.json
index d047281..d98de3d 100644
--- a/PUBLIC_SOURCE_MANIFEST.json
+++ b/PUBLIC_SOURCE_MANIFEST.json
@@ -1,6 +1,6 @@
 {
   "schemaVersion": 1,
-  "sourceRevision": "87aa7dda6889fd951d202754d76daaaa1e98e26b",
+  "sourceRevision": "166e10b7084c977816a75560d015da8f350c534c",
   "files": [
     {
       "path": ".dockerignore",
@@ -1659,8 +1659,8 @@
     },
     {
       "path": "backend/tests/test_runner_fleet_specialize.py",
-      "sha256": "8d75435eb4f7b4adb52ffaff7bbb234941c382c68a4e71bdbbc3abc177aa279a",
-      "bytes": 186243
+      "sha256": "e37f114322da2182d8448439025abe2ad772564332cff5955e93cc43d28cf45b",
+      "bytes": 188449
     },
     {
       "path": "backend/tests/test_runner_fleet_v2_execution_surface.py",
diff --git a/backend/tests/test_runner_fleet_specialize.py b/backend/tests/test_runner_fleet_specialize.py
index ce42dfe..8e08c05 100644
--- a/backend/tests/test_runner_fleet_specialize.py
+++ b/backend/tests/test_runner_fleet_specialize.py
@@ -1080,7 +1080,56 @@ def test_profile_state_creation_uses_effective_runner_image_owners_and_resumes(
             specialize._prepare_profile_state("a" * 40)
     config_path.write_bytes(expected)
     os.chmod(config_path, 0o600)
+    # Docker normalizes its own data-root to 0710. Rollback preserves this
+    # directory; preparation must resume without changing daemon-owned bytes.
+    dind_root.chmod(0o710)
     specialize._prepare_profile_state("a" * 40)
+    assert dind_root.stat().st_mode & 0o7777 == 0o710
+
+
+@pytest.mark.skipif(os.name != "posix" or os.geteuid() != 0, reason="requires POSIX root ownership")
+@pytest.mark.parametrize("fault", [None, "fresh", "mode711", "mode755", "mode770",
+    "mode701", "special", "owner", "group", "symlink", "file", "parent_mode",
+    "parent_owner", "parent_group", "parent_symlink"])
+def test_dind_data_root_accepts_only_daemon_mode_in_private_root_parent(
+    specialize, tmp_path, monkeypatch, fault,
+):
+    parent = tmp_path / "dind"
+    parent.mkdir(mode=0o700)
+    root = parent / "docker"
+    root.mkdir(mode=0o710)
+    monkeypatch.setattr(specialize, "DIND_STORAGE_ROOT", root)
+    if fault == "fresh":
+        root.chmod(0o700)
+    elif fault and fault.startswith("mode"):
+        root.chmod(int(fault[4:], 8))
+    elif fault == "special":
+        root.chmod(0o1710)
+    elif fault in {"owner", "group"}:
+        os.chown(root, 1000 if fault == "owner" else 0, 1000 if fault == "group" else 0)
+    elif fault in {"symlink", "file"}:
+        root.rmdir()
+        if fault == "symlink":
+            root.symlink_to(tmp_path, target_is_directory=True)
+        else:
+            root.write_bytes(b"not a directory")
+    elif fault == "parent_mode":
+        parent.chmod(0o710)
+    elif fault in {"parent_owner", "parent_group"}:
+        os.chown(parent, 1000 if fault == "parent_owner" else 0,
+                 1000 if fault == "parent_group" else 0)
+    elif fault == "parent_symlink":
+        real_parent = tmp_path / "real-dind"
+        parent.rename(real_parent)
+        parent.symlink_to(real_parent, target_is_directory=True)
+    if fault in {None, "fresh"}:
+        specialize._trusted_dind_data_root()
+        if fault is None:
+            with pytest.raises(specialize.RunnerFleetSpecializeError, match="path_untrusted"):
+                specialize._trusted_directory(root)
+    else:
+        with pytest.raises(specialize.RunnerFleetSpecializeError, match="path_untrusted"):
+            specialize._trusted_dind_data_root()
 
 
 def _mounts(specialize, service):