Know where collections email will not land, using Mailchimp

**Objective:** For Rillet customers with overdue invoices (optionally only those owing at least `{min-amount-due}`), report whether their contacts are reachable by email in Mailchimp, so collections knows where email will not land.

**Step 1: Find the overdue invoices**

Call `rillet-get-invoices` (it takes no filters) and keep rows where `overdue` is true, or where `amount-due` is above zero and `due-date` is before today. If `{min-amount-due}` is given, keep only rows whose `amount-due` is at least that amount. Group by `customer-id`: number of overdue invoices, total `amount-due` per `currency`, oldest `due-date`. If nothing is overdue, say so and stop.

**Step 2: Find the contacts**

Call `rillet-get-customer-emails` once (no filters) and keep the emails for each overdue `customer-id`, with `email-type`. A customer with no emails is reported as "no contact email in Rillet".

**Step 3: Check reachability in Mailchimp**

For each email:

* Call `mailchimp-get-list-member` with `email` and record each audience's `status`.
* Call `mailchimp-get-campaign-email-activity` with `email-address`, `action` set to bounce and `activity-date.from` 180 days ago, and record any `bounce-type`.

Classify the email as reachable (subscribed or transactional, no hard bounce), unsubscribed (marketing blocked; a direct invoice email may still work), or undeliverable (cleaned or hard-bounced).

**Step 4: Report**

Table sorted by total `amount-due`, highest first: customer name, overdue invoice count, amount due and currency, oldest due date, each email with its classification. Then flag every customer with no reachable email, since an emailed reminder will not get through.

**Rules & Guidelines:**

* Tools named mailchimp- come from the mailchimp MCP server; tools named rillet- come from the rillet MCP server. If a tool from either server is missing, stop and say which server is not connected rather than working around it.
* The only key shared by the two systems is the email address. Mailchimp `customer-id` values (e-commerce store customers) are NOT Rillet customer ids; never pass one system's id into the other.
* Read-only. Do not call any Mailchimp tool whose name starts with mailchimp-add-, mailchimp-update-, mailchimp-start-, mailchimp-pause- or mailchimp-replicate-, and do not call any Rillet tool whose name starts with rillet-add-, rillet-update-, rillet-apply-, rillet-unapply-, rillet-record-, rillet-set- or rillet-setup-. In particular never call `mailchimp-add-list-member`, `mailchimp-update-list-member` or `mailchimp-add-segment-member` from this prompt.
* This prompt reports only. Do not mark invoices sent, record payments or contact anyone.

**Validation:**

* If `{min-amount-due}` is empty, include every overdue invoice. Compare it only against invoices in the same currency the user named; if they gave no currency, apply it to each currency as stated.
* An email not found in Mailchimp is "not in Mailchimp", which is different from undeliverable.