You are helping me build the following AI agent workflow.

## Goal
WhatsApp Appointment Scheduling with Google Calendar: Customers book via WhatsApp link; the system checks availability, creates a Google Calendar event, and logs details in Postgres.

## Specification
- What it does: Book appointments directly via WhatsApp by selecting your preferred time slot from available options. The system instantly confirms your selection by creating the event in your calendar and saving your details securely.
- Trigger: Triggered by an event (Manual · on demand)
- Autonomy: Fully hands-off
- Expected setup effort: about an afternoon
- Tools/services involved:
  - WhatsApp Business Cloud: Collect user input and send reservation links
  - Google Calendar: Check availability and create events
  - Postgres: Store booking data for future reference
  - Code: Process logic and handle scheduling constraints

## Known pitfalls, handle each one explicitly in your implementation
1. WhatsApp requires verified templates for outbound messages so you must pre-approve your booking flow text before deploying.
2. Timezone mismatches between user input and Google Calendar can cause double bookings so always normalize timestamps to UTC before checking availability.
3. Postgres transactions must be atomic to prevent calendar events from being created if the database save fails so wrap both operations in a single transaction block.

## Reference implementation
https://n8n.io/workflows/5855 (workflow template)
Fetch and inspect this before building. If it matches my stack, adapt it;
if not, rebuild the pattern with my tools.

## Process requirements
1. Before building: ask me which of the listed tools I actually use and
   what my platform is (n8n / Make / code / other). Do not assume.
2. Adapt the pattern to my answers; do not force the reference stack.
3. Address every pitfall above; tell me how you handled each.
4. Provide a test plan I can run before letting this touch real data.
5. Ask before any step that sends messages, modifies data, or spends money.

Source: https://usecasesforagents.com/use-case/whatsapp-appointment-scheduling-with-google-calendar/ via usecasesforagents.com