fix: harden Windows exec shell default

Maintainer edit: prefer pwsh when available so single-line commands support modern PowerShell operators, add -NonInteractive, and parse explicit cmd.exe paths with Windows path semantics for cross-platform tests.

tests/tools/test_exec_platform.py

@@ -6,6 +6,7 @@ platform-specific binaries (all subprocess calls are mocked).
 """
 
 import asyncio
+import shutil
 import sys
 from unittest.mock import AsyncMock, patch
 
@@ -127,8 +128,9 @@ class TestSpawnWindows:
             await ExecTool._spawn("dir", r"C:\work", env)
 
         args = mock_exec.call_args[0]
-        assert "powershell" in args[0].lower()
+        assert any(shell in args[0].lower() for shell in ("pwsh", "powershell"))
         assert "-NoProfile" in args
+        assert "-NonInteractive" in args
         assert "-Command" in args
         assert "dir" in args[-1]
 
@@ -161,8 +163,9 @@ class TestSpawnWindows:
             await ExecTool._spawn('python -c "print(1)\nprint(2)"', r"C:\work", env)
 
         args = mock_exec.call_args[0]
-        assert "powershell" in args[0].lower()
+        assert any(shell in args[0].lower() for shell in ("pwsh", "powershell"))
         assert "-NoProfile" in args
+        assert "-NonInteractive" in args
         assert "-Command" in args
         assert "print(1)" in args[-1]
         assert "print(2)" in args[-1]
@@ -189,6 +192,28 @@ class TestSpawnWindows:
         kwargs = mock_shell.call_args[1]
         assert kwargs["cwd"] == r"C:\work"
 
+    @pytest.mark.asyncio
+    async def test_prefers_pwsh_when_available(self):
+        env = {"PATH": ""}
+
+        def fake_which(command):
+            if command == "pwsh":
+                return r"C:\Program Files\PowerShell\7\pwsh.exe"
+            if command == "powershell":
+                return r"C:\Windows\system32\WindowsPowerShell\v1.0\powershell.exe"
+            return None
+
+        with (
+            patch("nanobot.agent.tools.shell._IS_WINDOWS", True),
+            patch("nanobot.agent.tools.shell.shutil.which", side_effect=fake_which),
+            patch("asyncio.create_subprocess_exec", new_callable=AsyncMock) as mock_exec,
+        ):
+            mock_exec.return_value = AsyncMock()
+            await ExecTool._spawn("dir", r"C:\work", env)
+
+        args = mock_exec.call_args[0]
+        assert "pwsh" in args[0].lower()
+
 
 # ---------------------------------------------------------------------------
 # path_append
@@ -532,7 +557,7 @@ class TestWindowsMultilineExec:
         assert "2" in result
         assert "Exit code: 0" in result
         args = mock_exec.call_args[0]
-        assert "powershell" in args[0].lower()
+        assert any(shell in args[0].lower() for shell in ("pwsh", "powershell"))
 
     @pytest.mark.asyncio
     async def test_multiline_node_uses_powershell(self):
@@ -551,7 +576,7 @@ class TestWindowsMultilineExec:
 
         assert "1" in result
         args = mock_exec.call_args[0]
-        assert "powershell" in args[0].lower()
+        assert any(shell in args[0].lower() for shell in ("pwsh", "powershell"))
 
     @pytest.mark.asyncio
     async def test_single_line_uses_powershell(self):
@@ -615,6 +640,7 @@ class TestResolveShellWindows:
         assert "hello" in result
         args = mock_exec.call_args[0]
         assert "powershell" in args[0].lower()
+        assert "-NonInteractive" in args
 
     @pytest.mark.asyncio
     async def test_shell_cmd_accepted(self):
@@ -644,3 +670,18 @@ class TestResolveShellWindows:
 
         assert "Error: unsupported shell" in result
         assert "Allowed: powershell, pwsh, cmd" in result
+
+
+@pytest.mark.skipif(
+    sys.platform != "win32" or shutil.which("pwsh") is None,
+    reason="requires Windows with PowerShell 7",
+)
+class TestWindowsRealExec:
+
+    @pytest.mark.asyncio
+    async def test_single_line_and_separator_uses_pwsh(self):
+        result = await ExecTool(timeout=10).execute(command="echo before && echo after")
+
+        assert "before" in result
+        assert "after" in result
+        assert "Exit code: 0" in result