Return the call_ids reserved by the HITL wire protocol.
An id is reserved when items carries a function_call named
:data:HITL_FUNCTION_NAME — the sentinel this host emits for a pending
interrupt. That sentinel and the function_call_output answering it
are transport plumbing rather than conversation content, so
:func:~._request.items_to_messages drops both instead of replaying
them to the model as a tool-call round trip.
This matters beyond the resume turn itself. On the turn that consumes an interrupt the host already filters the pair through the resume path's consumed-id set, but a client that echoes prior output items back — the ordinary stateless Responses pattern — keeps re-sending the sentinel on every later turn, when nothing is pending and no consumed-id set exists.
Only the function_call side carries the discriminating name. A
function_call_output arriving without it cannot be recognised
here, but an unpaired one is already dropped as an orphan
ToolMessage.
