Enhance backend loading diagnostics and remount logic

- Introduced a new `loading_fail_sec` parameter in the `wait_backend_idle` function to handle prolonged loading states, improving error handling for backend readiness.
- Updated the `ensure_dlbackend_bind` function to stop SwarmUI before remounting, preventing target busy errors and ensuring consistent data mounts.
- Enhanced the `recover_errored_backends` function to account for the new remount logic, improving backend recovery processes.
- Refactored tests to validate the new loading failure conditions and ensure proper handling of backend states during diagnostics.

tests/test_wait_backend_idle.py

@@ -50,7 +50,7 @@ def test_install_swarm_comfy_script_payload():
     assert 'bstat in ("empty", "disabled", "all_disabled", "unknown")' in text
 
 
-def test_wait_backend_idle_fail_fast_on_errored(monkeypatch):
+def test_wait_backend_idle_fail_fast_on_long_loading(monkeypatch):
     from gpu_rent.errors import CloudError
     from gpu_rent import ready
 
@@ -58,7 +58,10 @@ def test_wait_backend_idle_fail_fast_on_errored(monkeypatch):
         pass
 
     def fake_ssh(*a, **k):
-        return "BUSY backend=errored"
+        cmd = a[2] if len(a) > 2 else ""
+        if "journalctl" in str(cmd):
+            return "loading models…"
+        return "BUSY backend=loading (Comfy стартует)"
 
     diag_calls = {"n": 0}
 
@@ -70,15 +73,29 @@ def test_wait_backend_idle_fail_fast_on_errored(monkeypatch):
     monkeypatch.setattr(ready, "collect_swarm_diagnostics", fake_diag)
     try:
         ready.wait_backend_idle(
-            Cfg(), "1.2.3.4", [].append, timeout=600.0, poll_every=0.01, errored_fail_sec=0.05
+            Cfg(),
+            "1.2.3.4",
+            [].append,
+            timeout=600.0,
+            poll_every=0.01,
+            loading_fail_sec=0.05,
         )
         assert False, "expected CloudError"
     except CloudError as exc:
-        assert "errored" in str(exc).lower()
-        assert "диагностик" in str(exc).lower() or "diag" in str(exc).lower()
+        assert "loading" in str(exc).lower()
     assert diag_calls["n"] == 1
 
 
+def test_install_script_uses_none_frontend():
+    from importlib.resources import files
+
+    text = files("gpu_rent.remote").joinpath("install_swarm_comfy.py").read_text(
+        encoding="utf-8"
+    )
+    assert '"FrontendVersion": "None"' in text
+    assert "stop_for_remount" in text or "перед remount" in text
+
+
 def test_wait_backend_idle_fail_fast_on_disabled(monkeypatch):
     from gpu_rent.errors import CloudError
     from gpu_rent import ready