diff --git a/tests/test_provision.py b/tests/test_provision.py
index aadf533..9f16a34 100644
--- a/tests/test_provision.py
+++ b/tests/test_provision.py
@@ -75,6 +75,14 @@ def isolate_claude_skill(monkeypatch: pytest.MonkeyPatch, tmp_path: Path) -> Pat
     return skill_dir
 
 
+@pytest.fixture
+def posix_form(monkeypatch: pytest.MonkeyPatch) -> None:
+    """Pin the POSIX .sh hook form: these tests assert omi-guard.sh wiring,
+    which native Windows deliberately no longer uses (#259) — without this
+    pin they fail on the windows-latest CI runners."""
+    monkeypatch.setattr(provision, "_windows", lambda: False)
+
+
 def _config(tmp_path: Path, **kw: object) -> SetupConfig:
     return SetupConfig(vault=tmp_path / "vault", **kw)  # type: ignore[arg-type]
 
@@ -654,7 +662,11 @@ def test_secret_output_guard_dry_run_writes_nothing(
     assert not (tmp_path / ".claude" / "hooks" / "secret-output-guard.sh").exists()
 
 
-def test_setup_writes_omi_guard_scripts(monkeypatch: pytest.MonkeyPatch, tmp_path: Path) -> None:
+def test_setup_writes_omi_guard_scripts(
+    monkeypatch: pytest.MonkeyPatch,
+    tmp_path: Path,
+    posix_form: None,
+) -> None:
     monkeypatch.setattr(provision.Path, "home", classmethod(lambda cls: tmp_path))
     Provisioner(_config(tmp_path), log=_quiet)._write_omi_guard_scripts()
     hooks = tmp_path / ".claude" / "hooks"
@@ -668,7 +680,9 @@ def test_setup_writes_omi_guard_scripts(monkeypatch: pytest.MonkeyPatch, tmp_pat
         assert "__OMIND_BIN__" not in body
 
 
-def test_omi_guard_installed_idempotently(tmp_path: Path, isolate_settings: Path) -> None:
+def test_omi_guard_installed_idempotently(
+    tmp_path: Path, isolate_settings: Path, posix_form: None
+) -> None:
     config = _config(tmp_path)
     Provisioner(config, log=_quiet).ensure_omi_guard_installed()
     before = isolate_settings.read_text(encoding="utf-8")
@@ -685,7 +699,9 @@ def test_omi_guard_installed_idempotently(tmp_path: Path, isolate_settings: Path
     assert "mcp__omi__help" in data["permissions"]["allow"]
 
 
-def test_omi_guard_preserves_user_hooks(tmp_path: Path, isolate_settings: Path) -> None:
+def test_omi_guard_preserves_user_hooks(
+    tmp_path: Path, isolate_settings: Path, posix_form: None
+) -> None:
     user_pre = {"matcher": "Bash", "hooks": [{"type": "command", "command": "/x/mine.sh"}]}
     isolate_settings.write_text(json.dumps({"hooks": {"PreToolUse": [user_pre]}}))
     Provisioner(_config(tmp_path), log=_quiet).ensure_omi_guard_installed()
@@ -877,7 +893,7 @@ def test_provision_manifest_roundtrip_and_drift(
 
 def test_autoheal_installs_guard_when_drifted(
     tmp_path: Path, fake_tools: None, monkeypatch: pytest.MonkeyPatch
-) -> None:
+, posix_form: None) -> None:
     monkeypatch.setattr(provision.Path, "home", classmethod(lambda cls: tmp_path))
     monkeypatch.delenv("OMIND_NO_AUTOHEAL", raising=False)
     config = _config(tmp_path)
@@ -904,7 +920,7 @@ def test_autoheal_respects_opt_out(
 
 def test_provision_migrates_legacy_guard(
     tmp_path: Path, fake_tools: None, isolate_settings: Path, monkeypatch: pytest.MonkeyPatch
-) -> None:
+, posix_form: None) -> None:
     monkeypatch.setattr(provision.Path, "home", classmethod(lambda cls: tmp_path))
     hooks_dir = tmp_path / ".claude" / "hooks"
     hooks_dir.mkdir(parents=True)
@@ -1183,7 +1199,7 @@ def _guard_entry() -> dict[str, object]:
 
 def test_guard_hook_install_is_idempotent_when_our_entry_is_first(
     tmp_path: Path, monkeypatch: pytest.MonkeyPatch
-) -> None:
+, posix_form: None) -> None:
     """Setup must want NO write when the wiring already matches, whatever the
     order. It rebuilt the list as `kept + [desired]`, appending our entry, so
     with it first in the file — the shipped layout — the equality check failed
@@ -1227,7 +1243,7 @@ def test_guard_hook_install_is_idempotent_when_our_entry_is_first(
 
 def test_guard_hook_install_keeps_our_entry_in_place(
     tmp_path: Path, monkeypatch: pytest.MonkeyPatch
-) -> None:
+, posix_form: None) -> None:
     """A stale entry is refreshed where it sits, not moved to the end, and the
     user's own PreToolUse hooks keep their positions."""
     stale = _guard_entry()