Gemini 3.x rejects a request whose functionCall parts lack a
thought_signature. The signature was carried as base64 protected_data on a
text_reasoning content and re-attached by adjacency, which requires the
carrier to immediately precede its call. An approval round trip replays the
call with no carrier at all, so the next turn failed with a 400.
Track signatures in a bounded per-client call_id map populated at parse time
from the resolved call_id, and backfill only when the emitted part has no
signature. Also stop clearing the held signature on contents that emit no
Part, so an approval response or an unsigned thought summary between the
carrier and its call no longer drops it.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: dd0909cd-c7c3-42cb-aef1-1e9a3e64d917
Giles Odigwe
30996433ac