fix(hwfit): repair remote Windows hardware scan over SSH (#4674)

Remote Cookbook hwfit probes failed on Windows hosts because the PowerShell script was sent as nested -Command quoting through OpenSSH. Use -EncodedCommand for remote probes, auto-detect platform when omitted (including Darwin for Mac SSH hosts), and return a clearer error when SSH works but the probe fails.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_hwfit_windows.py

@@ -72,3 +72,50 @@ def test_gguf_alternate_still_recommended_on_windows():
     still appear on Windows even though the AWQ variant is hidden."""
     names = {r["name"] for r in rank_models(_windows_system(), limit=900)}
     assert "Qwen/Qwen2.5-3B-Instruct" in names
+
+
+def test_remote_windows_probe_uses_encoded_command(monkeypatch):
+    """Remote Windows hwfit must not use nested -Command quoting over SSH."""
+    from services.hwfit import hardware
+
+    calls = []
+    monkeypatch.setattr(hardware, "_remote_host", "user@winpc")
+    monkeypatch.setattr(hardware, "_remote_port", None)
+
+    def fake_run(cmd):
+        calls.append(cmd)
+        if isinstance(cmd, str) and "EncodedCommand" in cmd:
+            return (
+                '{"ram_gb":64,"avail_gb":32,"cpu_name":"Test CPU",'
+                '"cpu_cores":8,"arch":64}'
+            )
+        return None
+
+    monkeypatch.setattr(hardware, "_run", fake_run)
+    result = hardware._detect_windows()
+    assert result is not None
+    assert result["total_ram_gb"] == 64
+    assert len(calls) == 1
+    assert "EncodedCommand" in calls[0]
+    assert '-Command "' not in calls[0]
+
+
+def test_probe_remote_platform_detects_windows(monkeypatch):
+    from services.hwfit import hardware
+
+    monkeypatch.setattr(hardware, "_run", lambda cmd: "Windows_NT\n")
+    assert hardware._probe_remote_platform() == "windows"
+
+
+def test_probe_remote_platform_detects_darwin(monkeypatch):
+    from services.hwfit import hardware
+
+    def fake_run(cmd):
+        if cmd == "echo %OS%":
+            return "%OS%"
+        if cmd == ["uname", "-s"]:
+            return "Darwin"
+        raise AssertionError(f"unexpected probe cmd: {cmd!r}")
+
+    monkeypatch.setattr(hardware, "_run", fake_run)
+    assert hardware._probe_remote_platform() == "linux"