The API expects tool_call messages to be immediately followed by their results.

However, there's a bug in the previous message rebuilding logic that will accidentally insert an empty user prompt message which breaks this rule and causes an error like

Error: (None) An assistant message with 'tool_calls' must be followed by tool messages responding to each 'tool_call_id'. The following tool_call_ids did not have response messages: call_EsQHgm5PGNvnvuVVh3tvvaEr
Code: None
Message: An assistant message with 'tool_calls' must be followed by tool messages responding to each 'tool_call_id'. The following tool_call_ids did not have response messages: call_EsQHgm5PGNvnvuVVh3tvvaEr

This bug only appears if the for cases where we're doing multiple rounds of tool calls and prompts which is why it was missed originally. Added a test to handle multiple tool calls and confirmed that the bug repro'd before and is gone after.