You are helping me build the following AI agent workflow.

## Goal
Sync Mailchimp Unsubscribes to HubSpot: When a user unsubscribes from Mailchimp, the agent updates their HubSpot status, alerts marketing on Slack, logs to Sheets.

## Specification
- What it does: You instantly stop seeing Mailchimp emails when you unsubscribe by having your HubSpot status updated immediately. The system notifies your marketing team via Slack and logs the event in Google Sheets so everyone stays compliant without manual work. You also receive a confirmation email acknowledging your request to opt out.
- Trigger: Triggered by an event (Event · on Mailchimp unsubscribe)
- Autonomy: Fully hands-off
- Expected setup effort: about an afternoon
- Tools/services involved:
  - Mailchimp: Trigger unsubscribe events
  - HubSpot: Sync contact status and opt-outs
  - Slack: Alert marketing team and log audit
  - Google Sheets: Log unsubscribe records for analysis
  - Gmail: Send confirmation email to user

## Known pitfalls, handle each one explicitly in your implementation
1. Webhook signature verification is critical for security, so validate the HMAC header to ensure requests originate from Mailchimp.
2. Slack channel permissions might restrict bot posting, so pre-configure the app scopes and test access in a dedicated channel.

## Reference implementation
https://n8n.io/workflows/15875 (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/sync-mailchimp-unsubscribes-to-hubspot/ via usecasesforagents.com