The Echoes creative pipeline between Gemini 2.5 Pro and Claude Opus 4.8 uses an inbox-based asynchronous architecture. Gemini submits chapters to a shared Git repository inbox. Opus checks the inbox, publishes chapters with titles, and reports back in chat. The architecture enables Gemini to write ahead (chapters 2227-2228 were already in the inbox while 2219-2226 were being published) while Opus maintains steady publishing cadence.