fix: add Windows shell fallback for local sandbox (#1505)

* fix: add Windows shell fallback for local sandbox

* fix: handle PowerShell execution on Windows

* fix: handle Windows local shell execution

---------

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/tests/test_local_sandbox_encoding.py

@@ -1,4 +1,5 @@
 import builtins
+from types import SimpleNamespace
 
 import deerflow.sandbox.local.local_sandbox as local_sandbox
 from deerflow.sandbox.local.local_sandbox import LocalSandbox
@@ -31,3 +32,133 @@ def test_write_file_uses_utf8_on_windows_locale(tmp_path, monkeypatch):
     LocalSandbox("t").write_file(str(path), text)
 
     assert path.read_text(encoding="utf-8") == text
+
+
+def test_get_shell_prefers_posix_shell_from_path_before_windows_fallback(monkeypatch):
+    monkeypatch.setattr(local_sandbox.os, "name", "nt")
+    monkeypatch.setattr(LocalSandbox, "_find_first_available_shell", lambda candidates: r"C:\Program Files\Git\bin\sh.exe" if candidates == ("/bin/zsh", "/bin/bash", "/bin/sh", "sh") else None)
+
+    assert LocalSandbox._get_shell() == r"C:\Program Files\Git\bin\sh.exe"
+
+
+def test_get_shell_uses_powershell_fallback_on_windows(monkeypatch):
+    calls: list[tuple[str, ...]] = []
+
+    def fake_find(candidates: tuple[str, ...]) -> str | None:
+        calls.append(candidates)
+        if candidates == ("/bin/zsh", "/bin/bash", "/bin/sh", "sh"):
+            return None
+        return r"C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe"
+
+    monkeypatch.setattr(local_sandbox.os, "name", "nt")
+    monkeypatch.setattr(local_sandbox.os, "environ", {"SystemRoot": r"C:\Windows"})
+    monkeypatch.setattr(LocalSandbox, "_find_first_available_shell", fake_find)
+
+    assert LocalSandbox._get_shell() == r"C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe"
+    assert calls[1] == (
+        "pwsh",
+        "pwsh.exe",
+        "powershell",
+        "powershell.exe",
+        r"C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe",
+        "cmd.exe",
+    )
+
+
+def test_get_shell_uses_cmd_as_last_windows_fallback(monkeypatch):
+    def fake_find(candidates: tuple[str, ...]) -> str | None:
+        if candidates == ("/bin/zsh", "/bin/bash", "/bin/sh", "sh"):
+            return None
+        return r"C:\Windows\System32\cmd.exe"
+
+    monkeypatch.setattr(local_sandbox.os, "name", "nt")
+    monkeypatch.setattr(local_sandbox.os, "environ", {"SystemRoot": r"C:\Windows"})
+    monkeypatch.setattr(LocalSandbox, "_find_first_available_shell", fake_find)
+
+    assert LocalSandbox._get_shell() == r"C:\Windows\System32\cmd.exe"
+
+
+def test_execute_command_uses_powershell_command_mode_on_windows(monkeypatch):
+    calls: list[tuple[object, dict]] = []
+
+    def fake_run(*args, **kwargs):
+        calls.append((args[0], kwargs))
+        return SimpleNamespace(stdout="ok", stderr="", returncode=0)
+
+    monkeypatch.setattr(local_sandbox.os, "name", "nt")
+    monkeypatch.setattr(LocalSandbox, "_get_shell", staticmethod(lambda: r"C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe"))
+    monkeypatch.setattr(local_sandbox.subprocess, "run", fake_run)
+
+    output = LocalSandbox("t").execute_command("Write-Output hello")
+
+    assert output == "ok"
+    assert calls == [
+        (
+            [
+                r"C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe",
+                "-NoProfile",
+                "-Command",
+                "Write-Output hello",
+            ],
+            {
+                "shell": False,
+                "capture_output": True,
+                "text": True,
+                "timeout": 600,
+            },
+        )
+    ]
+
+
+def test_execute_command_uses_posix_shell_command_mode_on_windows(monkeypatch):
+    calls: list[tuple[object, dict]] = []
+
+    def fake_run(*args, **kwargs):
+        calls.append((args[0], kwargs))
+        return SimpleNamespace(stdout="ok", stderr="", returncode=0)
+
+    monkeypatch.setattr(local_sandbox.os, "name", "nt")
+    monkeypatch.setattr(LocalSandbox, "_get_shell", staticmethod(lambda: r"C:\Program Files\Git\bin\sh.exe"))
+    monkeypatch.setattr(local_sandbox.subprocess, "run", fake_run)
+
+    output = LocalSandbox("t").execute_command("echo hello")
+
+    assert output == "ok"
+    assert calls == [
+        (
+            [r"C:\Program Files\Git\bin\sh.exe", "-c", "echo hello"],
+            {
+                "shell": False,
+                "capture_output": True,
+                "text": True,
+                "timeout": 600,
+            },
+        )
+    ]
+
+
+def test_execute_command_uses_cmd_command_mode_on_windows(monkeypatch):
+    calls: list[tuple[object, dict]] = []
+
+    def fake_run(*args, **kwargs):
+        calls.append((args[0], kwargs))
+        return SimpleNamespace(stdout="ok", stderr="", returncode=0)
+
+    monkeypatch.setattr(local_sandbox.os, "name", "nt")
+    monkeypatch.setattr(LocalSandbox, "_get_shell", staticmethod(lambda: r"C:\Windows\System32\cmd.exe"))
+    monkeypatch.setattr(local_sandbox.subprocess, "run", fake_run)
+
+    output = LocalSandbox("t").execute_command("echo hello")
+
+    assert output == "ok"
+    assert calls == [
+        (
+            [r"C:\Windows\System32\cmd.exe", "/c", "echo hello"],
+            {
+                "shell": False,
+                "capture_output": True,
+                "text": True,
+                "timeout": 600,
+            },
+        )
+    ]