cb13d09 made _append_tool_results emit content=None (JSON null) for a follow-up
assistant message that carries only tool_calls and no prose, because Gemini's
OpenAI-compatible endpoint and Ollama reject tool_calls alongside an
empty-string content with HTTP 400.
But _sanitize_llm_messages strips None values and then required "content" on
every message, so it dropped that assistant message entirely — leaving the
role:"tool" result dangling with no parent tool_calls, which breaks the
follow-up round for every provider (and regresses ones that accepted "" before,
since the message is now removed rather than sent). cb13d09's tests covered
_append_tool_results in isolation, so the sanitizer interaction was uncaught.
Make the sanitizer role-aware: assistant messages survive with content OR
tool_calls, and a tool-calls-only assistant message gets an explicit
content=None re-added so the provider receives spec-correct `content: null`.
tool messages still require content + tool_call_id; user/system still require
content.
Adds tests/test_llm_core_sanitize_tool_calls.py, which drives the real producer
(_append_tool_results) into the sanitizer and asserts the assistant tool-call
message survives with its tool result paired. Red before this change, green
after.
1007703223