ls_tool was the only file-system tool that did not call
mask_local_paths_in_output() before returning its result, causing host
absolute paths (e.g. /Users/.../backend/.deer-flow/knowledge-base/...)
to leak to the LLM instead of the expected virtual paths
(/mnt/knowledge-base/...).
This patch:
- Adds the mask_local_paths_in_output() call to ls_tool, consistent
with bash_tool, glob_tool and grep_tool.
- Initialises thread_data = None before the is_local_sandbox branch
(same pattern as glob_tool) so the variable is always in scope.
- Adds three new tests covering user-data path masking, skills path
masking and the empty-directory edge case.