Handoff patterns are your agent's worst enemy, unless you implement them this way

Debugging a seemingly flawless handoff between agents led to an intriguing discovery. The planner produced a clean plan, the executor followed it step by step, but every handoff between them resulted in a loss of information. This "Handoff Tax" was not immediately apparent, but it had a significant impact on the system's performance.

The receiver wasn't weak; it was information-starved due to the handoff stripping away the signal. This loss of signal occurred because the handoff compressed or transferred information between agents, causing accumulated information loss through repeated summarization. Microsoft's Agent Framework training identified this issue as "context collapse," which is the most common failure in handoff chains.

To address this problem, a different protocol for what crosses the boundary is necessary. The Handoff Tax can be mitigated by ensuring that the attention cost avoided by decomposing information is greater than the handoff cost incurred during transfer. A study found that a structured handoff representation strongly affects downstream feasibility, with constraint checking benefiting from structured and auditable representations.

The deeper failure isn't just missing data; it's binding state that stops binding. An artifact can mention an unresolved condition while changing its role, making the information still present but the constraint gone. This issue was documented in a GitHub issue from a production LangChain planner-executor split. The planner called web_fetch three times, found the answer, and wrote it into the handoff text.

The executor, receiving only the text, called web_fetch three more times, walked the same wrong paths, and burned the same latency again. The two sessions didn't share tool call history, fetched data, or session state, preventing the executor from knowing whether the planner's answer was verified or provisional, fresh or stale. The failures compound across three layers: the handoff itself, the representation, and the verification.

The three-layer fix involves explicit coupling instead of pretending the coupling doesn't exist. Contracts, not prompts, should be used to make the coupling explicit. The A2A protocol's central abstraction is a stateful Task object that persists across whatever happens next. The task carries the state, not the prompt, and the receiving agent reads the task's current state and continues. Base context plus incremental deltas should be maintained rather than repeatedly resummarizing.