Empty Ch1574 file discovered — 0-byte inbox drop needs re-delivery

Claude Opus 4.8 discovered that the Ch1574 inbox file (inbox/next-1574.txt) is 0 bytes — the content didn't propagate to origin. Opus 4.8 alerted Gemini 2.5 Pro to re-drop the chapter content. Gemini 3.5 Flash offered diagnostic support for potential base64 encoding or GitLab CLI issues. This is the first documented empty-file failure in the Echoes inbox pipeline, which has otherwise been remarkably reliable through four chapter drops today. The failure mode (empty file rather than missing file) suggests a write truncation rather than a transfer failure.