diff --git a/.github/workflows/python-tests.yml b/.github/workflows/python-tests.yml
index 4df4621a23..f4dc248783 100644
--- a/.github/workflows/python-tests.yml
+++ b/.github/workflows/python-tests.yml
@@ -934,6 +934,7 @@ jobs:
           tests/test_file_lock_cross_process.py
           tests/test_host_thread_activity.py
           tests/control_plane/test_effect_runtime_integration.py
+          tests/control_plane/test_turn_instance_arg.py
           tests/control_plane/test_shadow_observation_retirement.py
           tests/test_python_install_owner_platform.py
           tests/test_self_update_runtime_activation.py
diff --git a/loopx/control_plane/quota/effect_program.py b/loopx/control_plane/quota/effect_program.py
index 37644130de..f9247073b5 100644
--- a/loopx/control_plane/quota/effect_program.py
+++ b/loopx/control_plane/quota/effect_program.py
@@ -54,6 +54,7 @@
     "settlement_binding_args",
     "settlement_result_payload",
     "settlement_step_command",
+    "turn_instance_arg",
 ]
 
 
@@ -77,6 +78,18 @@ def _quoted_turn_ref(turn_instance_id_ref: str) -> str:
     return shlex.quote(turn_instance_id_ref)
 
 
+def turn_instance_arg(turn_instance_id: str | None = None) -> str:
+    """Render the ``--turn-instance-id`` argument for the shell that runs it.
+
+    A caller holding a concrete Turn passes it through unchanged. Without one,
+    the argument names the reference the current host shell can expand, so a
+    native Windows host does not receive an empty Turn from POSIX syntax.
+    """
+
+    reference = turn_instance_id or _default_turn_ref()
+    return f"--turn-instance-id {_quoted_turn_ref(reference)}"
+
+
 def _settlement_actor_args(arguments: str, agent_id: str) -> str:
     """Identity owns the actor; optional host arguments cannot omit or retarget it."""
     tokens = shlex.split(arguments)
@@ -302,8 +315,4 @@ def settlement_binding_args(plan: Mapping[str, Any] | None) -> str:
             f" --goal-instance-id "
             f"{shlex.quote(normalized_goal_ref['goal_instance_id'])}"
         )
-    return (
-        binding_arg
-        + f" --turn-instance-id {_quoted_turn_ref(turn_instance_id)}"
-        + goal_ref_arg
-    )
+    return binding_arg + " " + turn_instance_arg(turn_instance_id) + goal_ref_arg
diff --git a/loopx/control_plane/quota/settlement.py b/loopx/control_plane/quota/settlement.py
index 4b438c521a..116d85f176 100644
--- a/loopx/control_plane/quota/settlement.py
+++ b/loopx/control_plane/quota/settlement.py
@@ -29,6 +29,7 @@
     settlement_binding_args,
     settlement_result_payload,
     settlement_step_command,
+    turn_instance_arg,
 )
 
 QUOTA_SETTLEMENT_READBACK_REQUEST_SCHEMA = (
@@ -249,6 +250,7 @@ def render_settlement_progress_markdown(payload: dict[str, Any]) -> list[str]:
     "settlement_binding_args",
     "settlement_result_payload",
     "settlement_step_command",
+    "turn_instance_arg",
 ]
 
 
diff --git a/loopx/control_plane/work_items/interaction_contract.py b/loopx/control_plane/work_items/interaction_contract.py
index a8e0be0a83..5da4c4c44f 100644
--- a/loopx/control_plane/work_items/interaction_contract.py
+++ b/loopx/control_plane/work_items/interaction_contract.py
@@ -19,6 +19,7 @@
     SettlementStepKind,
     settlement_binding_args,
     settlement_step_command,
+    turn_instance_arg,
 )
 from ..quota.spend_sources import (
     build_quota_spend_action,
@@ -697,7 +698,7 @@ def _admitted_interaction_next_cli_actions(
     )
     typed_heartbeat_receipt_retry = (
         f"on missing/write_failed heartbeat_receipt only: {typed_quota_guard} "
-        '--turn-instance-id "${LOOPX_TURN:?}"'
+        f"{turn_instance_arg()}"
         if scheduler_args
         else (
             "on missing/write_failed heartbeat_receipt only: retry the current "
diff --git a/tests/control_plane/test_scheduler_execution_context.py b/tests/control_plane/test_scheduler_execution_context.py
index 21063780c0..27e06124a9 100644
--- a/tests/control_plane/test_scheduler_execution_context.py
+++ b/tests/control_plane/test_scheduler_execution_context.py
@@ -31,6 +31,7 @@
 from loopx.control_plane.todos.quota_summary import (
     compact_quota_todo_summary_for_payload,
 )
+from loopx.control_plane.quota import effect_program as quota_effect_program
 from loopx.control_plane.work_items.interaction_contract import (
     finalize_user_gate_notification_cooldown,
     interaction_next_cli_actions,
@@ -1626,7 +1627,19 @@ def test_generic_outer_controller_rerun_actions_are_typed() -> None:
     assert all(" -H " not in action for action in actions)
 
 
-def test_codex_app_monitor_quiet_retry_uses_turn_receipt() -> None:
+@pytest.mark.parametrize(
+    ("windows_host", "turn_arg"),
+    (
+        (False, '--turn-instance-id "${LOOPX_TURN:?}"'),
+        (True, "--turn-instance-id $LOOPX_TURN"),
+    ),
+)
+def test_codex_app_monitor_quiet_retry_uses_turn_receipt(
+    monkeypatch: pytest.MonkeyPatch,
+    windows_host: bool,
+    turn_arg: str,
+) -> None:
+    monkeypatch.setattr(quota_effect_program, "_is_windows_host", lambda: windows_host)
     actions = interaction_next_cli_actions(
         {
             "goal_id": "codex-heartbeat-fixture",
@@ -1642,7 +1655,7 @@ def test_codex_app_monitor_quiet_retry_uses_turn_receipt() -> None:
         (
             "on missing/write_failed heartbeat_receipt only: loopx --format json "
             "quota should-run --goal-id codex-heartbeat-fixture --agent-id "
-            'codex-fixture --codex-app --turn-instance-id "${LOOPX_TURN:?}"'
+            f"codex-fixture --codex-app {turn_arg}"
         )
     ]
 
diff --git a/tests/control_plane/test_turn_instance_arg.py b/tests/control_plane/test_turn_instance_arg.py
new file mode 100644
index 0000000000..223a71a29d
--- /dev/null
+++ b/tests/control_plane/test_turn_instance_arg.py
@@ -0,0 +1,62 @@
+"""The shared Turn argument must render for the shell that runs it.
+
+Native Windows has no POSIX ``${NAME:?}`` expansion, so a command built there
+has to name the PowerShell variable that carries the Turn. The same helper owns
+the settlement binding arguments and the heartbeat-receipt retry hint, so both
+inherit one rule instead of one copy each.
+"""
+
+from __future__ import annotations
+
+import os
+
+import pytest
+
+from loopx.control_plane.quota import effect_program as quota_effect_program
+from loopx.control_plane.quota.effect_program import turn_instance_arg
+
+POSIX_REF = "${LOOPX_TURN:?}"
+WINDOWS_REF = "$LOOPX_TURN"
+POSIX_ARG = f'--turn-instance-id "{POSIX_REF}"'
+WINDOWS_ARG = f"--turn-instance-id {WINDOWS_REF}"
+
+
+def _host(monkeypatch: pytest.MonkeyPatch, windows: bool) -> None:
+    monkeypatch.setattr(quota_effect_program, "_is_windows_host", lambda: windows)
+
+
+@pytest.mark.parametrize(
+    ("windows", "expected"),
+    ((False, POSIX_ARG), (True, WINDOWS_ARG)),
+)
+def test_a_host_default_reference_matches_the_running_shell(
+    monkeypatch: pytest.MonkeyPatch, windows: bool, expected: str
+) -> None:
+    _host(monkeypatch, windows)
+
+    assert turn_instance_arg() == expected
+
+
+@pytest.mark.parametrize("windows", [False, True])
+def test_an_explicit_turn_is_quoted_unchanged(
+    monkeypatch: pytest.MonkeyPatch, windows: bool
+) -> None:
+    _host(monkeypatch, windows)
+
+    assert turn_instance_arg("turn-settlement-host-1") == (
+        "--turn-instance-id turn-settlement-host-1"
+    )
+
+
+def test_a_posix_reference_on_windows_names_the_powershell_variable(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    _host(monkeypatch, True)
+
+    assert turn_instance_arg(POSIX_REF) == WINDOWS_ARG
+
+
+def test_the_default_matches_the_running_host_shell() -> None:
+    expected = WINDOWS_ARG if os.name == "nt" else POSIX_ARG
+
+    assert turn_instance_arg() == expected