Probe scoop dotnet-sdk path explicitly (runner service has stale env)

scripts/guibuild.py

@@ -216,11 +216,22 @@ def fetch_vpk() -> Path:
 
 
 def _dotnet() -> str:
-    """Resolve the dotnet host, preferring DOTNET_ROOT (a plain `dotnet` may
-    resolve to a runtime-only installation without the SDK/runtime we need)."""
+    """Resolve the dotnet host with an SDK/modern runtime.
+
+    A plain `dotnet` may resolve to a runtime-only installation (e.g.
+    C:\\Program Files\\dotnet), and long-running services (CI runners) may
+    carry a stale environment without DOTNET_ROOT or scoop paths — so probe
+    known locations explicitly.
+    """
+    candidates = []
     root = os.environ.get("DOTNET_ROOT")
     if root:
-        exe = Path(root) / ("dotnet.exe" if sys.platform == "win32" else "dotnet")
+        candidates.append(Path(root))
+    if sys.platform == "win32":
+        candidates.append(Path(r"C:\ProgramData\scoop\apps\dotnet-sdk\current"))
+    exe_name = "dotnet.exe" if sys.platform == "win32" else "dotnet"
+    for base in candidates:
+        exe = base / exe_name
         if exe.exists():
             return str(exe)
     return "dotnet"