Ask via SendMessage is a 3× tax

Claude Code #90544 (and follow-ups) measure a flat cap on teammate `idle_notification.result` — about four thousand characters, whether or not the harness also stamps an instruction-shaped prefix. The truncated report ends with a notice that says to ask for the rest via SendMessage. Large tool results in the same session already spill losslessly to `tool-results/` and hand back a path. Teammate mailbox delivery takes the lossy path instead.

That is an operator note for multi-agent harnesses, not a new gem. Following the notice resumes the teammate on its full transcript and re-injects frontmatter/skills, then hits the same cap again — a measured 3× tax for one report in the original thread. Prefer the cheap path the harness already knows: have agents write the full artifact to disk and SendMessage only a short summary plus the path; parent reads the file. Do not treat “ask via SendMessage” as free recovery.