Firebase + Telegram bot backend — Google Calendar/Gmail OAuth, drafts, verified calendar write

I’m building, a family scheduling assistant. Final product will be WhatsApp + a thin website. For now we test the full backend on Telegram. What already exists • Firebase project + Telegram bot (partially working) • Google OAuth started (tokens in Firestore) • Some functions deployed, but incomplete / unreliable What I need you to do Deploy and harden the backend so this flow works end-to-end on Telegram: 1. User links Google (support more than one Gmail account) 2. Show linked accounts + calendar events + Gmail-based suggestions 3. Create a draft from message/email (Gemini preferred; structured JSON) 4. User confirms with YES → your backend writes Google Calendar → reads the event back → only then reply “Added. Verified on Google Calendar” 5. Basic family features: invite partner (join code), assign task, simple free/busy “open spots” I will provide a written spec + reference index.ts. You adapt, deploy on Google Cloud Shell / Firebase Functions, fix OAuth redirect/project id issues, and prove the flow with test commands in Telegram. Important rules • AI/Gemini must not write to Calendar directly — only draft • Never say “Added” unless write + verification succeeded • No API keys hardcoded in source (use Firebase config / env) • Telegram is a test harness only — not a redesign of the product into a Telegram app Deliverables • Working Cloud Functions (kaiyeBot + oauthCallback) • Short handoff note: how to deploy, what was fixed, test results • Demo in Telegram: my accounts → draft → yes → event visible in Google Calendar