fix: detect total RAM on Windows via GlobalMemoryStatusEx

`_total_ram_gb()` had branches for Darwin (sysctl) and Linux
(/proc/meminfo) but no Windows path, so `jarvis init` reported
"0.0 GB RAM" on every Windows host. The downstream
`recommend_model()` then fell back to VRAM-only sizing, often
selecting a smaller tier than the system can actually run.

Add a Windows branch that calls `GlobalMemoryStatusEx` via
ctypes — no new dependency. Add a platform-skip-aware test for
each OS branch.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/openjarvis/core/config.py

@@ -188,13 +188,34 @@ def _total_ram_gb() -> float:
         if platform.system() == "Darwin":
             raw = _run_cmd(["sysctl", "-n", "hw.memsize"])
             return round(int(raw) / (1024**3), 1) if raw else 0.0
+        if platform.system() == "Windows":
+            import ctypes
+
+            class _MemoryStatusEx(ctypes.Structure):
+                _fields_ = [
+                    ("dwLength", ctypes.c_ulong),
+                    ("dwMemoryLoad", ctypes.c_ulong),
+                    ("ullTotalPhys", ctypes.c_ulonglong),
+                    ("ullAvailPhys", ctypes.c_ulonglong),
+                    ("ullTotalPageFile", ctypes.c_ulonglong),
+                    ("ullAvailPageFile", ctypes.c_ulonglong),
+                    ("ullTotalVirtual", ctypes.c_ulonglong),
+                    ("ullAvailVirtual", ctypes.c_ulonglong),
+                    ("sullAvailExtendedVirtual", ctypes.c_ulonglong),
+                ]
+
+            stat = _MemoryStatusEx()
+            stat.dwLength = ctypes.sizeof(_MemoryStatusEx)
+            if ctypes.windll.kernel32.GlobalMemoryStatusEx(ctypes.byref(stat)):
+                return round(stat.ullTotalPhys / (1024**3), 1)
+            return 0.0
         meminfo = Path("/proc/meminfo")
         if meminfo.exists():
             for line in meminfo.read_text().splitlines():
                 if line.startswith("MemTotal"):
                     kb = int(line.split()[1])
                     return round(kb / (1024**2), 1)
-    except (OSError, ValueError):
+    except (OSError, ValueError, AttributeError):
         pass
     return 0.0
 

tests/hardware/test_hardware_profiles.py

@@ -3,13 +3,17 @@ and engine recommendation."""
 
 from __future__ import annotations
 
+import sys
 from unittest.mock import patch
 
+import pytest
+
 from openjarvis.core.config import (
     GpuInfo,
     _detect_amd_gpu,
     _detect_apple_gpu,
     _detect_nvidia_gpu,
+    _total_ram_gb,
     recommend_engine,
 )
 
@@ -75,6 +79,31 @@ class TestDetectHardware:
         assert _detect_apple_gpu() is None
 
 
+# ---------------------------------------------------------------------------
+# RAM detection
+# ---------------------------------------------------------------------------
+
+
+class TestTotalRamGb:
+    """Tests for _total_ram_gb() across platforms."""
+
+    @pytest.mark.skipif(sys.platform != "win32", reason="Requires Windows")
+    def test_total_ram_gb_windows(self):
+        """On Windows, GlobalMemoryStatusEx must return a positive RAM value."""
+        ram = _total_ram_gb()
+        assert ram > 0, f"Expected > 0 GB on Windows, got {ram}"
+
+    @pytest.mark.skipif(sys.platform != "darwin", reason="Requires macOS")
+    def test_total_ram_gb_darwin(self):
+        ram = _total_ram_gb()
+        assert ram > 0, f"Expected > 0 GB on macOS, got {ram}"
+
+    @pytest.mark.skipif(not sys.platform.startswith("linux"), reason="Requires Linux")
+    def test_total_ram_gb_linux(self):
+        ram = _total_ram_gb()
+        assert ram > 0, f"Expected > 0 GB on Linux, got {ram}"
+
+
 # ---------------------------------------------------------------------------
 # Engine recommendation
 # ---------------------------------------------------------------------------