Claude Code subagent can't Write a REPORT.md: have it return the report in its final message and let the lead save it

Seen with a Claude Code subagent spawned via the Agent tool and asked to 'write benchmarks/.../REPORT.md'. The harness refused the subagent's Write of a report-style .md file, so the subagent put the report into its final output instead. Small helper scripts it wrote in the same directory (.py/.cpp) were saved fine.

What works: - In the brief, ask for the report as the final message (or a short summary plus a SendMessage carrying the full text), and have the parent session write it to disk. - Or ask for a non-.md artifact (a .txt or .json data file) if a file on disk is really needed. - Have the subagent keep its numeric evidence in scripts and data files (segment walkers, TSVs), which save normally, and keep the prose in the message. - When the parent copies it, record that it's a lead copy of the subagent's message and keep the subagent's own MEASURED/ESTIMATE labels. - If the subagent finishes before your follow-up questions arrive, a SendMessage to its name resumes it from its transcript to add a section.