diff --git a/loopx/skill_install_readback.py b/loopx/skill_install_readback.py
index 79ef7bdfd6..957771358d 100644
--- a/loopx/skill_install_readback.py
+++ b/loopx/skill_install_readback.py
@@ -12,6 +12,7 @@
 
 from . import __version__
 from .doctor_git import git_metadata_for_root
+from .slash_command_files import MANAGED_MARKER_PREFIX as LOOPX_MANAGED_SLASH_COMMAND_MARKER
 
 SKILL_INSTALL_READBACK_SCHEMA_VERSION = "loopx_skill_install_readback_v1"
 SKILL_INSTALL_READBACK_FILENAME = ".loopx-skill-install.json"
@@ -36,7 +37,6 @@
         PYTHON_DISTRIBUTION_SKILL_INSTALL_MODE,
     ),
 }
-LOOPX_MANAGED_SLASH_COMMAND_MARKER = "<!-- loopx-managed-slash-command:v1"
 PACKAGED_HOST_SKILL_IDS = [
     "loopx-project",
     "loopx-pr-program",
diff --git a/tests/architecture/test_managed_slash_command_marker_owner.py b/tests/architecture/test_managed_slash_command_marker_owner.py
new file mode 100644
index 0000000000..9eb6b0731a
--- /dev/null
+++ b/tests/architecture/test_managed_slash_command_marker_owner.py
@@ -0,0 +1,62 @@
+"""The managed slash-command marker is stated once and read everywhere else.
+
+`loopx/slash_command_files.py` writes the marker into a generated facade;
+`loopx/skill_install_readback.py` reads it back to decide whether a file is
+LoopX-managed. Both stated the same literal under their own names, so a version
+bump had two places to land and a drift between them would silently make the
+readback treat a managed file as user-owned.
+
+Shipped host assets carry the marker as their first line in their own runtime.
+They cannot import the Python owner, so they are listed here and checked against
+it instead: renaming the prefix has to move them in the same change.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from loopx import skill_install_readback
+from loopx.slash_command_files import MANAGED_MARKER_PREFIX, managed_marker
+
+REPOSITORY_ROOT = Path(__file__).resolve().parents[2]
+OWNER_MODULE = "loopx/slash_command_files.py"
+
+ASSET_HEADERS = (
+    "loopx/opencode_goal_mode/goal-bridge-runtime.mjs",
+    "loopx/opencode_goal_mode/loopx-goal.js",
+    "loopx/pi_goal_mode/loopx-goal.ts",
+    "loopx/pi_goal_mode/pi-goal-loop-runtime.mjs",
+)
+
+# Surfaces a generated facade may be written for; each one has to survive the
+# round trip from the writer to the readback through the single owner.
+FACADE_SURFACES = ("claude-skills", "codex-skills", "pi-extension")
+
+
+def test_the_marker_body_is_stated_only_by_the_owner_in_python() -> None:
+    # A census, not a roster: a module that starts stating the literal again has
+    # to appear here, and a site that already imports the owner fails too.
+    found: dict[str, int] = {}
+    for path in sorted(REPOSITORY_ROOT.glob("loopx/**/*.py")):
+        relative = path.relative_to(REPOSITORY_ROOT).as_posix()
+        count = path.read_text(encoding="utf-8").count(MANAGED_MARKER_PREFIX)
+        if count:
+            found[relative] = count
+    assert found == {OWNER_MODULE: 1}
+
+
+def test_the_readback_imports_the_owner_object() -> None:
+    assert skill_install_readback.LOOPX_MANAGED_SLASH_COMMAND_MARKER is MANAGED_MARKER_PREFIX
+
+
+def test_the_writer_and_the_reader_agree_on_every_facade_surface() -> None:
+    for surface in FACADE_SURFACES:
+        marker = managed_marker(command="/loopx", surface=surface)
+        assert marker.startswith(MANAGED_MARKER_PREFIX)
+        assert MANAGED_MARKER_PREFIX in marker
+
+
+def test_each_shipped_asset_header_states_the_owner_marker() -> None:
+    for relative in ASSET_HEADERS:
+        header = (REPOSITORY_ROOT / relative).read_text(encoding="utf-8").splitlines()[0]
+        assert MANAGED_MARKER_PREFIX in header, relative