The generated stub streams binary outputs as octet-stream; the lexicon declares application/zip and the TS client refuses the mismatch. echo only fills Content-Type when unset, so the handler declares it. Claude-Session: https://claude.ai/code/session_014aPQ5yqG9QFxKnbwQfCYKa (cherry picked from commit e652dd47b02167e3df2faeb1b62d92394997fced)