Keep your Drip overdue tag in step with real balances

**Objective:** Keep the Drip tag `{tag}` (default Overdue account) in step with Business Central: subscribers whose customer has a balance due of at least `{min-balance-due}` (default 1000) should carry it, and nobody else should. Use Business Central company `{bc-company}` if given.

**Step 1: Who should carry the tag**

Call `business-central-get-customer` with `balance-due.min` set to `{min-balance-due}`. Keep each customer's `email`, `customer-number`, `name` and `balance-due`. For each email, call `drip-get-subscriber` with `email` set to it. A customer goes on the ADD list when the subscriber exists and its `tags` do not already include the tag.

**Step 2: Who should lose the tag**

Call `drip-get-subscriber` with `tags.contains` set to the tag. For each subscriber returned, call `business-central-get-customer` with `email` set to the subscriber's `email`. Put the subscriber on the REMOVE list when the customer's `balance-due` is now below the threshold, or when no customer has that email.

**Step 3: Confirm**

Show both lists (email, customer number, name, balance due) and ask the user to confirm. Do not write anything until they do. Accept a confirmation for one list only, or with emails excluded.

**Step 4: Apply and confirm**

For each confirmed ADD, call `drip-add-subscriber-tag` with `email` and `tag`. For each confirmed REMOVE, call `drip-remove-subscriber-tag` with `email` and `tag`. Then re-read each changed subscriber with `drip-get-subscriber` and report what succeeded and what failed.

**Rules & Guidelines:**

* Tools whose names start with drip are on the drip server; tools whose names start with business-central are on the business-central server. Pass `{bc-company}` only to business-central tools.
* The only write tools allowed are `drip-add-subscriber-tag` and `drip-remove-subscriber-tag`, and only after Step 3. Never write to Business Central. Do NOT call `drip-add-subscriber`, `drip-unsubscribe-subscriber` or any campaign or workflow tool.
* Never create a Drip subscriber for a customer who is not already in Drip; list them as not in Drip instead.

**Validation:**

* If both lists are empty, say the tag is already in step and stop.
* Skip customers with no email in Business Central and count them in the report.
* Compare emails and tag names case-insensitively.