diff --git a/gateway/run.py b/gateway/run.py
index 9ac43b5f6..bdc7122cb 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -2653,6 +2653,16 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
         self._restart_via_service = False
         self._detached_restart_helper_started = False
         self._restart_command_source: Optional[SessionSource] = None
+        # Monotonic-ish wall clock of when this GatewayRunner was constructed.
+        # Used by the /restart redelivery guard to bound the window in which a
+        # missing dedup marker is treated as a stale redelivery.
+        self._startup_time: float = time.time()
+        # Set True at startup when this process booted as the result of a
+        # chat-originated /restart (i.e. .restart_notify.json existed on boot).
+        # A one-shot signal consumed by _is_stale_restart_redelivery so the
+        # marker-missing fallback only suppresses a /restart when we KNOW we
+        # just came out of a restart cycle — never on a genuine fresh boot.
+        self._booted_from_restart: bool = False
         self._stop_task: Optional[asyncio.Task] = None
         self._restart_task: Optional[asyncio.Task] = None
         self._executor_lock = threading.Lock()
@@ -6579,6 +6589,13 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
 
         # Notify the chat that initiated /restart that the gateway is back.
         planned_restart_notification_pending = _planned_restart_notification_pending()
+        # Capture, before _send_restart_notification() unlinks the marker,
+        # whether this process booted from a chat-originated /restart. Used as
+        # a one-shot signal by the /restart redelivery guard so a missing
+        # dedup marker only suppresses a /restart when we KNOW we just came out
+        # of a restart cycle (see _is_stale_restart_redelivery).
+        if _restart_notification_pending() or planned_restart_notification_pending:
+            self._booted_from_restart = True
         await self._send_restart_notification()
 
         # Broadcast a lightweight "gateway is back" message to configured home
@@ -11431,6 +11448,25 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
         try:
             marker_path = _hermes_home / ".restart_last_processed.json"
             if not marker_path.exists():
+                # Belt-and-suspenders for when the dedup marker goes missing
+                # (manually cleaned up, or the previous cycle's write failed).
+                # Without a marker the update_id comparison below can't run, so
+                # a redelivered /restart would sail through and re-restart the
+                # gateway — an infinite loop (issue #18528).
+                #
+                # Suppress ONLY when we can independently confirm we just came
+                # out of a restart cycle: this process booted from a
+                # chat-originated /restart (_booted_from_restart) AND is still
+                # within a short post-boot window. This never swallows a
+                # genuine first /restart on a fresh boot (no restart marker on
+                # boot → flag stays False). Consume the flag one-shot so a
+                # legitimate /restart sent later in the same session is honored.
+                if (
+                    getattr(self, "_booted_from_restart", False)
+                    and time.time() - getattr(self, "_startup_time", 0.0) < 60
+                ):
+                    self._booted_from_restart = False
+                    return True
                 return False
             data = json.loads(marker_path.read_text())
         except Exception:
diff --git a/tests/gateway/test_restart_redelivery_dedup.py b/tests/gateway/test_restart_redelivery_dedup.py
index 88cb0223d..7b651d9c8 100644
--- a/tests/gateway/test_restart_redelivery_dedup.py
+++ b/tests/gateway/test_restart_redelivery_dedup.py
@@ -244,3 +244,74 @@ async def test_different_platform_bypasses_dedup(tmp_path, monkeypatch):
 
     assert "Restarting gateway" in result
     runner.request_restart.assert_called_once()
+
+
+@pytest.mark.asyncio
+async def test_marker_missing_but_booted_from_restart_ignores_redelivery(tmp_path, monkeypatch):
+    """Missing marker + just booted from a /restart + young process → treat as stale.
+
+    Reproduces the infinite-loop scenario (issue #18528): the dedup marker went
+    missing, so the update_id comparison can't run. Because this process booted
+    from a chat-originated /restart and is still within the post-boot window,
+    the redelivered /restart is suppressed instead of re-restarting the gateway.
+    """
+    monkeypatch.setattr(gateway_run, "_hermes_home", tmp_path)
+    monkeypatch.delenv("INVOCATION_ID", raising=False)
+
+    runner, _adapter = make_restart_runner()
+    runner.request_restart = MagicMock(return_value=True)
+    runner._booted_from_restart = True
+    runner._startup_time = time.time()
+
+    event = _make_restart_event(update_id=100)
+    result = await runner._handle_restart_command(event)
+
+    assert result == ""  # silently ignored
+    runner.request_restart.assert_not_called()
+    # One-shot: the flag is consumed so a later legitimate /restart is honored.
+    assert runner._booted_from_restart is False
+
+
+@pytest.mark.asyncio
+async def test_marker_missing_fresh_boot_allows_restart(tmp_path, monkeypatch):
+    """Missing marker on a genuine fresh boot (not from /restart) → /restart proceeds.
+
+    The guard must NOT swallow the first /restart a user sends shortly after a
+    normal (non-restart) startup: _booted_from_restart stays False, so the
+    fallback returns False and the restart goes through.
+    """
+    monkeypatch.setattr(gateway_run, "_hermes_home", tmp_path)
+    monkeypatch.delenv("INVOCATION_ID", raising=False)
+
+    runner, _adapter = make_restart_runner()
+    runner.request_restart = MagicMock(return_value=True)
+    runner._booted_from_restart = False
+    runner._startup_time = time.time()
+
+    event = _make_restart_event(update_id=100)
+    result = await runner._handle_restart_command(event)
+
+    assert "Restarting gateway" in result
+    runner.request_restart.assert_called_once()
+
+
+@pytest.mark.asyncio
+async def test_marker_missing_booted_from_restart_but_old_process_allows(tmp_path, monkeypatch):
+    """Missing marker + booted from /restart but past the window → /restart proceeds.
+
+    A /restart arriving long after boot is a genuine user action, not a boot-time
+    redelivery, so the uptime bound stops the guard from suppressing it forever.
+    """
+    monkeypatch.setattr(gateway_run, "_hermes_home", tmp_path)
+    monkeypatch.delenv("INVOCATION_ID", raising=False)
+
+    runner, _adapter = make_restart_runner()
+    runner.request_restart = MagicMock(return_value=True)
+    runner._booted_from_restart = True
+    runner._startup_time = time.time() - 120  # well past the 60s window
+
+    event = _make_restart_event(update_id=100)
+    result = await runner._handle_restart_command(event)
+
+    assert "Restarting gateway" in result
+    runner.request_restart.assert_called_once()