fix(chat): graceful degradation for malformed tool call arguments

[huckstack]

Problem

When models generate malformed JSON in tool call arguments (e.g., unescaped single quotes like log_dir = '/home/huckstack/.hermes/logs/cron'), func_args_not_string() throws an HTTP 500 error. This causes cascading failures where every subsequent request crashes with Failed to parse tool call arguments as JSON: unexpected end of input.

The function was introduced in commit b283f6d with throw, which converts a recoverable parsing error into a hard server error.

Fix

Replace throw std::runtime_error(...) with LOG_WRN(...) in func_args_not_string(). This converts the hard 500 error into a graceful degradation — the server logs a warning and keeps the arguments as a string, allowing the conversation to continue.

Context

This is related to issue #21771 which reports the same symptom. The root cause there is the PEG parser failing on array<object> parameter values, but the symptom (HTTP 500 from func_args_not_string) is the same. This fix addresses the symptom by making the error handling more robust.

Diff

- throw std::runtime_error("Failed to parse tool call arguments as JSON: " + std::string(e.what()));
+ LOG_WRN("Failed to parse tool call arguments as JSON, keeping as string: %s\n", e.what());

[ggml-gh-bot]

Hi @huckstack, thanks for your contribution!

Per our contribution guidelines, the automated PR checker found the following issue(s) that need your attention:

• AI-generated content: This project does not accept PRs, descriptions or commit messages that are fully or predominantly AI-generated. If you have used AI to assist you in writing code, please make sure to disclose that explicitly.

---

Please note that maintainers reserve the right to make final decisions on PRs. If you believe there is a mistake, please comment below.

[aldehir]

Unfortunately, this is not sufficient. Some chat templates require arguments be an object and not a string. The failure will simply occur further down, in the Jinja engine for these.

Do you have a reliable reproducer I can run? Fixing the core issue is the solution here.