fix: preserve virtual path separator style (#1828)

* fix: preserve virtual path separator style

* Apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

backend/packages/harness/deerflow/sandbox/tools.py

@@ -366,12 +366,17 @@ def _path_variants(path: str) -> set[str]:
     return {path, path.replace("\\", "/"), path.replace("/", "\\")}
 
 
+def _path_separator_for_style(path: str) -> str:
+    return "\\" if "\\" in path and "/" not in path else "/"
+
+
 def _join_path_preserving_style(base: str, relative: str) -> str:
     if not relative:
         return base
-    if "/" in base and "\\" not in base:
-        return f"{base.rstrip('/')}/{relative}"
-    return str(Path(base) / relative)
+    separator = _path_separator_for_style(base)
+    normalized_relative = relative.replace("\\" if separator == "/" else "/", separator).lstrip("/\\")
+    stripped_base = base.rstrip("/\\")
+    return f"{stripped_base}{separator}{normalized_relative}"
 
 
 def _sanitize_error(error: Exception, runtime: "ToolRuntime[ContextT, ThreadState] | None" = None) -> str:
@@ -416,7 +421,10 @@ def replace_virtual_path(path: str, thread_data: ThreadDataState | None) -> str:
             return actual_base
         if path.startswith(f"{virtual_base}/"):
             rest = path[len(virtual_base) :].lstrip("/")
-            return _join_path_preserving_style(actual_base, rest)
+            result = _join_path_preserving_style(actual_base, rest)
+            if path.endswith("/") and not result.endswith(("/", "\\")):
+                result += _path_separator_for_style(actual_base)
+            return result
 
     return path
 

backend/tests/test_sandbox_tools_security.py

@@ -42,6 +42,53 @@ def test_replace_virtual_path_maps_virtual_root_and_subpaths() -> None:
     assert Path(replace_virtual_path("/mnt/user-data", _THREAD_DATA)).as_posix() == "/tmp/deer-flow/threads/t1/user-data"
 
 
+def test_replace_virtual_path_preserves_trailing_slash() -> None:
+    """Trailing slash must survive virtual-to-actual path replacement.
+
+    Regression: '/mnt/user-data/workspace/' was previously returned without
+    the trailing slash, causing string concatenations like
+    output_dir + 'file.txt' to produce a missing-separator path.
+    """
+    result = replace_virtual_path("/mnt/user-data/workspace/", _THREAD_DATA)
+    assert result.endswith("/"), f"Expected trailing slash, got: {result!r}"
+    assert result == "/tmp/deer-flow/threads/t1/user-data/workspace/"
+
+
+def test_replace_virtual_path_preserves_trailing_slash_windows_style() -> None:
+    """Trailing slash must be preserved as backslash when actual_base is Windows-style.
+
+    If actual_base uses backslash separators, appending '/' would produce a
+    mixed-separator path.  The separator must match the style of actual_base.
+    """
+    win_thread_data = {
+        "workspace_path": r"C:\deer-flow\threads\t1\user-data\workspace",
+        "uploads_path": r"C:\deer-flow\threads\t1\user-data\uploads",
+        "outputs_path": r"C:\deer-flow\threads\t1\user-data\outputs",
+    }
+    result = replace_virtual_path("/mnt/user-data/workspace/", win_thread_data)
+    assert result.endswith("\\"), f"Expected trailing backslash for Windows path, got: {result!r}"
+    assert "/" not in result, f"Mixed separators in Windows path: {result!r}"
+
+
+def test_replace_virtual_path_preserves_windows_style_for_nested_subdir_trailing_slash() -> None:
+    """Nested Windows-style subdirectories must keep backslashes throughout."""
+    win_thread_data = {
+        "workspace_path": r"C:\deer-flow\threads\t1\user-data\workspace",
+        "uploads_path": r"C:\deer-flow\threads\t1\user-data\uploads",
+        "outputs_path": r"C:\deer-flow\threads\t1\user-data\outputs",
+    }
+    result = replace_virtual_path("/mnt/user-data/workspace/subdir/", win_thread_data)
+    assert result == "C:\\deer-flow\\threads\\t1\\user-data\\workspace\\subdir\\"
+    assert "/" not in result, f"Mixed separators in Windows path: {result!r}"
+
+
+def test_replace_virtual_paths_in_command_preserves_trailing_slash() -> None:
+    """Trailing slash on a virtual path inside a command must be preserved."""
+    cmd = """python -c "output_dir = '/mnt/user-data/workspace/'; print(output_dir + 'some_file.txt')\""""
+    result = replace_virtual_paths_in_command(cmd, _THREAD_DATA)
+    assert "/tmp/deer-flow/threads/t1/user-data/workspace/" in result, f"Trailing slash lost in: {result!r}"
+
+
 # ---------- mask_local_paths_in_output ----------
 
 
@@ -257,6 +304,22 @@ def test_validate_local_bash_command_paths_blocks_host_paths() -> None:
         validate_local_bash_command_paths("cat /etc/passwd", _THREAD_DATA)
 
 
+def test_validate_local_bash_command_paths_allows_https_urls() -> None:
+    """URLs like https://github.com/... must not be flagged as unsafe absolute paths."""
+    validate_local_bash_command_paths(
+        "cd /mnt/user-data/workspace && git clone https://github.com/CherryHQ/cherry-studio.git",
+        _THREAD_DATA,
+    )
+
+
+def test_validate_local_bash_command_paths_allows_http_urls() -> None:
+    """HTTP URLs must not be flagged as unsafe absolute paths."""
+    validate_local_bash_command_paths(
+        "curl http://example.com/file.tar.gz -o /mnt/user-data/workspace/file.tar.gz",
+        _THREAD_DATA,
+    )
+
+
 def test_validate_local_bash_command_paths_allows_virtual_and_system_paths() -> None:
     validate_local_bash_command_paths(
         "/bin/echo ok > /mnt/user-data/workspace/out.txt && cat /dev/null",