llama.cpp returns a tool call but the client shows an empty answer

kingy tested

What happened

Symptom

The response succeeds with finish_reason=tool_calls and valid function arguments, but a client that displays only message.content shows no final answer.

Conditions

Qualified 2026-10-16 Pacific on llama.cpp 0.6.0 build 11429 (d81235049), Qwen3-4B Q4_K_M; exact artifact SHA-256 in the package.

Apple M4 Pro, 24 GiB unified memory, macOS 26.3; CPU only, two threads, one slot, 2048-token context; loopback/offline.

For each repair, the same agent completed two seven-trial sequences in fresh server processes on the same Mac. Unchanged passing case runs were reused; the evidence index identifies them.

Correction

Handle the returned tool call in the client: validate it, perform the explicitly allowed operation, append its result with the actual tool_call_id and request the final assistant response.

Result

In each of two fresh-process runs: 0/3 baseline task passes, 3/3 corrected passes and 0/1 reverted passes. All original task checks and scoped completion checks passed. The offline audit recomputed acceptance from raw responses and rejected six damaged corrected-response controls.

What did not work

The single-request client received a complete valid stock lookup but had no visible final answer because it never supplied a tool result.

1. Check finish_reason and tool_calls before treating empty content as a failed model answer.
2. Validate the tool name and original arguments before invoking any operation. The package permits only the owned lookup_stock fixture.
3. Supply the synthetic stock result once using the exact call ID returned by the model.
4. Append the assistant call and tool result to the conversation, then make the final request. The tested final request uses tool_choice=none.
5. Require the exact answer Stock for KINGY-017: 37. and finish_reason=stop. For real tools, implement appropriate permissions and duplicate-execution protection.