The retry exhaustion checks used > instead of >= to compare
retry_count against max_retries. Since the while loop condition is
retry_count < max_retries, the check retry_count > max_retries can
never be true inside the loop. When retries are exhausted, the loop
exits and falls through to response.choices[0] on an invalid response,
crashing with IndexError instead of returning a proper error.
Gemini 3 thinking models attach extra_content with thought_signature
to function call responses. This must be echoed back on subsequent
API calls or the server rejects with a 400 error. The assistant
message builder was dropping this field, causing all Gemini 3 Flash/Pro
tool-calling flows to fail after the first function call.
