LM Studio (and Ollama) reject the named tool_choice dict format
{"type": "function", "function": {"name": "..."}} with HTTP 400.
The reflect agent uses this format on iterations 0-2 to force sequential
tool selection, causing reflect to fail entirely on LM Studio.
The fix converts named tool_choice dicts to tool_choice="required" with
the tools list filtered to just the requested tool — semantically identical
and accepted by all providers including LM Studio and Ollama.
Closes#520
