fix(sandbox): preserve trailing whitespace in filenames from list_dir and glob in remote providers

[shoemoney]

Why

The remote sandbox providers parse find output for list_dir and glob by calling .strip() on every line. A filename that legitimately ends (or begins) in whitespace, such as "notes.txt ", comes back corrupted: the listed path does not exist, so every follow-up read_file/grep/glob on it misses the real file. LocalSandbox uses pathlib and preserves such names, so behavior silently diverges between local and remote providers.

#4861 fixed this exact class in the e2b _sync_outputs_to_host path, with the rationale that the delimiter already provides an unambiguous boundary, so stripping is harmful ("NUL already delimits records, so do NOT strip"). The same reasoning applies to the newline-delimited find output here: splitlines() has already removed the terminator, and anything else on the line is part of the filename. This PR applies that fix to the remaining parsers, nine strip sites across the five providers.

What changed

list_dir and glob in the five remote providers (e2b, OpenSandbox, AIO Sandbox, Tenki, BoxLite) now return filenames verbatim, matching LocalSandbox. Empty-line filtering is kept; only the per-entry strip is removed. No API or signature changes.

Surface area

• Sandbox — docker/ or sandboxed execution

Bug fix verification

• Test paths that reproduce the bug: backend/tests/test_e2b_sandbox_provider.py::test_list_dir_preserves_trailing_space_in_filename and ::test_glob_preserves_trailing_space_in_filename, backend/tests/test_opensandbox_provider.py::test_list_dir_and_glob_preserve_trailing_space_in_filename, backend/tests/test_aio_sandbox.py::test_list_dir_preserves_trailing_space_in_filename, backend/tests/test_tenki_provider.py::test_search_preserves_trailing_space_in_filename, backend/tests/test_boxlite_provider.py::test_list_dir_and_glob_preserve_trailing_space_in_filename
• Did it go red on main and green on this branch? yes, all six fail on main ('.../notes.txt' != '.../notes.txt ') and pass with the fix

Validation

cd backend && uv run pytest -m "not live" on the five touched test files: 349 passed, 1 skipped (baseline 343 passed). Adjacent suites (test_sandbox_search_tools.py, test_remote_sandbox_backend.py, aio provider/local-backend): 138 passed. ruff check and ruff format --check clean on all touched files.

AI assistance

Tool(s) used: Claude (pair programming)

How you used it: Written in conjunction with my pair programmer Claude.

• I've read and understand every line of this change and take responsibility for it — it's not unreviewed AI output.

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