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>

services/hwfit/hardware.py

@@ -538,6 +538,32 @@ def _powershell_exe():
     path so we don't depend on a particular PATH ordering."""
     return shutil.which("pwsh") or shutil.which("powershell") or "powershell"
 
+def _powershell_encoded_for_ssh(script: str):
+    """Run a PowerShell script on a remote Windows host over SSH.
+
+    Nested quotes in powershell -Command break when passed through Windows
+    OpenSSH's cmd wrapper; -EncodedCommand avoids that.
+    """
+    import base64
+    encoded = base64.b64encode(script.encode("utf-16-le")).decode("ascii")
+    return _run(f"powershell -NoProfile -EncodedCommand {encoded}")
+
+
+def _probe_remote_platform():
+    """Best-effort OS detection over SSH when the caller didn't pass platform."""
+    out = _run("echo %OS%")
+    if out and "Windows_NT" in out:
+        return "windows"
+    uname = (_run(["uname", "-s"]) or "").strip().lower()
+    if uname == "darwin":
+        # Mac uses the linux detection path (_detect_apple_silicon over SSH).
+        return "linux"
+    if uname == "linux":
+        out = _run("test -d /data/data/com.termux && echo termux || echo linux")
+        if out and "termux" in out:
+            return "termux"
+    return "linux"
+
 
 def _detect_windows():
     """Detect Windows hardware via PowerShell/WMI.
@@ -600,9 +626,8 @@ def _detect_windows():
     """
     )
     if _remote_host:
-        # Remote: ship a single command string over SSH. The remote shell parses
-        # the quoting; PowerShell on the far side runs the -Command payload.
-        out = _run(f'powershell -Command "{ps_cmd}"')
+        # Remote: use -EncodedCommand so OpenSSH/cmd quoting does not break the script.
+        out = _powershell_encoded_for_ssh(ps_cmd.strip())
     else:
         # Local: pass a LIST argv straight to subprocess so the OS hands ps_cmd
         # to PowerShell verbatim — no fragile string-level quote escaping. Prefer
@@ -773,6 +798,13 @@ def detect_system(host="", ssh_port="", platform="", fresh=False):
     """
     global _remote_host, _remote_port, _remote_platform
 
+    if host and not platform:
+        _remote_host = host
+        _remote_port = ssh_port or None
+        platform = _probe_remote_platform()
+        _remote_host = None
+        _remote_port = None
+
     cache_key = _cache_key(host, ssh_port, platform)
     now = time.time()
     if not fresh and cache_key in _cache_by_host:
@@ -793,8 +825,8 @@ def detect_system(host="", ssh_port="", platform="", fresh=False):
             _remote_platform = None
             _cache_by_host[cache_key] = (now, result)
             return result
-        # If Windows detection failed, return error
-        result = {"error": f"Cannot connect to {host}", "host": host}
+        # SSH may work while the PowerShell hardware probe still fails.
+        result = {"error": f"Windows hardware probe failed for {host}", "host": host}
         _remote_host = None
         _remote_platform = None
         _cache_by_host[cache_key] = (now, result)

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"