| Single-turn expert query | Agents-as-tools | Handoff / Group Chat | The host can simply retain control |
| Multi-turn domain takeover | Handoff | Agents-as-tools | The specialist needs to talk to the user directly |
| Fixed flow | Sequential Pipeline / Workflow | Swarm | Determinism is the point |
| Many independent subtasks | Parallel Fan-out / Gather | Sequential | Parallelism gives the most speedup |
| Long, complex tasks | Graph Workflow + Task Registry | Pure prompt orchestration | Resume, cancel, trace required |
| Quality review needed | Generator-Critic / Refinement Loop | Single agent self-grading | Self-grade often reproduces the same error |
| Comparing multiple options | Debate / Voting / MoA | Single path | Multiple candidates surface conflict |
| Async multi-party work | Blackboard / Event Bus | Group Chat | Shared state is steadier than long conversations |
| High-risk operation | Human-in-the-loop + Guardrails | Fully automated | Permission and accountability must be explicit |
| Cross-tool ecosystem | MCP | Custom tool protocol | Lowers integration cost |
| Cross-agent / cross-vendor | A2A / ACP | Private RPC | Better suited to interoperability |
| IDE to coding agent | Agent Client Protocol | Ad-hoc HTTP API | Closer to coding-agent standard onboarding |