Yields one tool-call handle per tool-started event.
Mirrors the per-event body of _ToolCallsProjection._tool_calls_iter
(_async/stream.py:1168-1217). The thread register/unregister and the
terminal-error-on-close finally stay at the projection / wrapper layer.
Events whose namespace differs are ignored.
Keyword-only (tool_call_id, name, input, namespace) -> handle.
