Messages are stored as Issues on your GitHub repo. Photos stay in the Issue JSON; video/voice files are stored under gchat-media/ via the Contents API (token needs Contents write).
No token: public repo read‑only (~60 requests/hour → often ~30–60s before new messages appear). Everyone who wants chat to feel instant should save a token here — same PAT works for send + fast receive (~1s). Sending always requires a token.