Only one agent should be active at a time, and the active agent must be able to transfer control dynamically when another specialist is better suited. Microsoft Agent Framework defines handoff orchestration for precisely that situation: task and conversational ownership move from one agent to another according to context. Concurrent orchestration would activate multiple specialists at the same time, contradicting the requirement. Sequential orchestration follows a predetermined order rather than allowing contextual transfer.
Group chat keeps multiple agents participating in a shared conversation rather than modeling single-owner control. The decisive requirement is therefore transfer of ownership, not merely calling another agent for a subtask. That makes B, handoff, the correct orchestration pattern. In production, add telemetry and regression tests around this behavior so changes to prompts, models, tools, or orchestration do not silently alter the intended contract. The selected approach is the one that best matches the platform ' s native execution semantics.
Official Microsoft reference: Microsoft Agent Framework - Handoff orchestration