diff --git a/scripts/ci/check_os_marker_fakes.py b/scripts/ci/check_os_marker_fakes.py
new file mode 100644
index 0000000000..18f90690b6
--- /dev/null
+++ b/scripts/ci/check_os_marker_fakes.py
@@ -0,0 +1,135 @@
+#!/usr/bin/env python3
+"""Fail when a test file fakes macOS without carrying ``@pytest.mark.macos_only``.
+
+The OS lanes are marker-driven: ``.github/workflows/tests-os.yml`` selects the
+files the macOS job imports via ``scripts/ci/list_os_marked_tests.py macos_only``
+and then runs ``-m macos_only``. A file whose tests only pass because they make
+the interpreter believe it is on macOS (``is_macos`` patched to ``True``,
+``sys.platform`` set to ``"darwin"``) but that carries no marker is invisible to
+that lane: it is green on Linux over a faked branch and never imported on the
+host it exists for (#111866). Root ``AGENTS.md`` § "Don't fake the host OS" is
+the rule; this check makes a violation a red job instead of a review catch.
+
+Flags, per ``tests/**/test_*.py`` without a whole-word ``macos_only``:
+
+  monkeypatch.setattr(mod, "is_macos", lambda: True) / patch(..., return_value=True)
+  monkeypatch.setattr(sys, "platform", "darwin")  /  patch("sys.platform", "darwin")
+  platform.system patched to return "Darwin"
+
+Opt out of one line with ``# os-marker: ok — <why>`` on that line (a pure
+function taking the platform as data is host-independent and stays unmarked).
+``_BASELINE`` lists the files that already faked macOS when this check landed;
+they are a burn-down list, not a policy — split the macOS arm out, mark it,
+and drop the entry (a stale entry fails the check).
+
+Run: python scripts/ci/check_os_marker_fakes.py [tests_root]
+"""
+
+from __future__ import annotations
+
+import os
+import re
+import sys
+from pathlib import Path
+
+MARKER = "macos_only"
+OPT_OUT = "os-marker: ok"
+
+_TRUE = r"(?:lambda[^:]*:\s*True|return_value\s*=\s*True|,\s*True\b)"
+_FAKES = (
+    re.compile(rf"\bis_macos\b.*{_TRUE}"),
+    re.compile(r"\bis_macos\.return_value\s*=\s*True\b"),
+    # setattr(sys, "platform", "darwin") / patch("sys.platform", "darwin") / x.platform = "darwin";
+    # a host-honest READ (`if sys.platform == "darwin":`) is not a fake and does not match.
+    re.compile(r"""\bplatform["']?\s*,\s*["']darwin["']"""),
+    re.compile(r"""\.platform\s*=\s*["']darwin["']"""),
+    re.compile(r"""\bplatform\.system\b.*(?:lambda[^:]*:|return_value\s*=)\s*["']Darwin["']"""),
+)
+
+# Files that faked macOS before this check existed (#111866). Burn down, never extend.
+_BASELINE = frozenset(
+    {
+        "tests/hermes_cli/test_doctor.py",
+        "tests/hermes_cli/test_gateway.py",
+        "tests/hermes_cli/test_gateway_proc_fallback.py",
+        "tests/hermes_cli/test_linux_sandbox_fixup.py",
+        "tests/hermes_cli/test_macos_fda_guidance.py",
+        "tests/hermes_cli/test_orphan_desktop_serve_reap.py",
+        "tests/hermes_cli/test_update_launchd_restart_verification.py",
+        "tests/hermes_cli/test_update_launchd_unloaded_gateway.py",
+        "tests/hermes_cli/test_urllib_security.py",
+        "tests/hermes_state/test_state_synchronous_pragma.py",
+        "tests/test_hermes_constants.py",
+        "tests/tools/test_macos_protected_search.py",
+        "tests/tools/test_skills_tool.py",
+    }
+)
+
+
+def _code_lines(text: str) -> list[tuple[int, str, str]]:
+    """Yield ``(lineno, code, raw)`` with the ``#`` comment stripped from *code*.
+
+    A ``#`` inside a string literal is rare in these patterns and only ever
+    hides a hit (never invents one), so a plain split is the honest trade
+    against a full tokenizer.
+    """
+    out = []
+    for i, raw in enumerate(text.splitlines(), 1):
+        out.append((i, raw.split("#", 1)[0], raw))
+    return out
+
+
+def find_unmarked_fakes(root: Path, repo_root: Path) -> dict[str, list[tuple[int, str]]]:
+    """Map repo-relative test path -> ``[(lineno, line)]`` of un-opted-out macOS fakes."""
+    marker_pat = re.compile(rf"\b{MARKER}\b")
+    hits: dict[str, list[tuple[int, str]]] = {}
+    for dirpath, _dirnames, filenames in os.walk(root):
+        for fname in filenames:
+            if not (fname.startswith("test_") and fname.endswith(".py")):
+                continue
+            path = Path(dirpath) / fname
+            try:
+                text = path.read_text(encoding="utf-8", errors="replace")
+            except OSError:
+                continue
+            if marker_pat.search(text):
+                continue
+            lines = [
+                (n, raw.strip())
+                for n, code, raw in _code_lines(text)
+                if OPT_OUT not in raw and any(p.search(code) for p in _FAKES)
+            ]
+            if lines:
+                resolved = path.resolve()
+                base = repo_root if resolved.is_relative_to(repo_root) else root.resolve()
+                hits[resolved.relative_to(base).as_posix()] = lines
+    return hits
+
+
+def main(argv: list[str]) -> int:
+    repo_root = Path(__file__).resolve().parents[2]
+    root = Path(argv[1]) if len(argv) > 1 else repo_root / "tests"
+    if not root.is_dir():
+        print(f"error: no such directory: {root}", file=sys.stderr)
+        return 2
+    hits = find_unmarked_fakes(root, repo_root)
+    new = {rel: lines for rel, lines in hits.items() if rel not in _BASELINE}
+    stale = sorted(_BASELINE - set(hits))
+    for rel, lines in sorted(new.items()):
+        for n, line in lines:
+            print(f"{rel}:{n}: fakes macOS without @pytest.mark.{MARKER}: {line}")
+    if new:
+        print(
+            f"\n{len(new)} test file(s) make the interpreter believe it is on macOS but carry no "
+            f"`{MARKER}` marker, so the macOS lane never imports them (AGENTS.md § Don't fake the "
+            f"host OS). Split the macOS arm into its own `@pytest.mark.{MARKER}` test that runs the "
+            f"real branch, or mark `# {OPT_OUT} — <why>` on a host-independent line.",
+            file=sys.stderr,
+        )
+    for rel in stale:
+        print(f"{rel}: listed in _BASELINE but no longer fakes macOS — remove the entry")
+    return 1 if new or stale else 0
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv))
diff --git a/tests/ci/test_check_os_marker_fakes.py b/tests/ci/test_check_os_marker_fakes.py
new file mode 100644
index 0000000000..1133307323
--- /dev/null
+++ b/tests/ci/test_check_os_marker_fakes.py
@@ -0,0 +1,39 @@
+"""The unmarked-macOS-fake guard (#111866): flags fakes, ignores honest reads and marked files."""
+
+from __future__ import annotations
+
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parents[2] / "scripts" / "ci"))
+
+from check_os_marker_fakes import find_unmarked_fakes  # noqa: E402
+
+
+def _write(root: Path, name: str, body: str) -> None:
+    (root / name).write_text(body, encoding="utf-8")
+
+
+def test_unmarked_fake_is_flagged_marked_and_opted_out_are_not(tmp_path):
+    _write(tmp_path, "test_fake.py", "def test_x(monkeypatch):\n"
+           "    monkeypatch.setattr(gw, 'is_macos', lambda: True)\n"
+           "    monkeypatch.setattr(sys, 'platform', 'darwin')\n")
+    _write(tmp_path, "test_marked.py", "import pytest\npytestmark = pytest.mark.macos_only\n"
+           "def test_x(monkeypatch):\n    monkeypatch.setattr(gw, 'is_macos', lambda: True)\n")
+    _write(tmp_path, "test_opted.py", "def test_x(monkeypatch):\n"
+           "    patch('m.is_macos', return_value=True)  # os-marker: ok — pure data mapping\n")
+
+    hits = find_unmarked_fakes(tmp_path, tmp_path)
+
+    assert set(hits) == {"test_fake.py"}
+    assert [n for n, _ in hits["test_fake.py"]] == [2, 3]
+
+
+def test_host_honest_platform_read_is_not_a_fake(tmp_path):
+    _write(tmp_path, "test_read.py", "import sys\n"
+           "def test_x():\n    expected = sys.platform == 'darwin'\n"
+           "    if sys.platform == 'darwin':\n        pass\n"
+           "    payload = {'platform': 'darwin'}\n"
+           "    # monkeypatch.setattr(gw, 'is_macos', lambda: True) in a comment\n")
+
+    assert find_unmarked_fakes(tmp_path, tmp_path) == {}
diff --git a/tests/hermes_cli/test_update_autostash.py b/tests/hermes_cli/test_update_autostash.py
index 5f4c7eb179..6ac9c04e48 100644
--- a/tests/hermes_cli/test_update_autostash.py
+++ b/tests/hermes_cli/test_update_autostash.py
@@ -57,9 +57,14 @@ def _patch_gateway_discovery():
     phase's fresh ``from hermes_cli.gateway import ...`` then loads an
     UNPATCHED copy of the module — silently discarding every mock here and
     letting real gateway discovery (and real ``os.kill``) run on the dev box.
+
+    The launchd scope is neutralised too: on a macOS host the restart phase
+    derives labels from the profile layout, so a default profile alone hands
+    it ``ai.hermes.gateway`` and the verify step exits 1 (#111866, #110701).
     """
     with patch("hermes_cli.gateway.find_gateway_pids", return_value=[]), \
          patch("hermes_cli.gateway.supports_systemd_services", return_value=False), \
+         patch("hermes_cli.update_cmd_fleet._restart_macos_launchd_gateways", lambda *a, **k: None), \
          patch("hermes_cli.gateway.find_profile_gateway_processes", return_value=[]), \
          patch("hermes_cli.update_inventory.collect_runtime_inventory", return_value=None), \
          patch("hermes_cli.update_inventory.report_unaccounted_runtimes", return_value=False), \