- Introduced support for custom tool calls in request serialization, including preservation of call IDs, input, and output. - Enhanced tool call batching logic to handle ambiguous, missing, and reused call IDs across assistant messages. - Updated processing of tool call outputs to ensure proper matching with pending calls and introduced synthesized IDs when necessary. - Added extensive test cases to validate behavior for custom tool call histories, mixed call types, and edge cases with ambiguous or orphaned IDs. Closes: #4256