Add subscribers to Constant Contact lists once, with honest consent

**Objective:** Add the contact `{email-address}` (name `{full-name}`, if given) to the contact list `{list-name}`.

**Step 1: Resolve the list**

Call `constant-contact-get-contact-list` with `name` set to `{list-name}`. If nothing matches, retry with `name.contains`; if that gives several, list them and stop so the user can pick. Keep the list-id.

**Step 2: Check the contact**

Call `constant-contact-get-contact` with `email-address` set to `{email-address}`.

* If the contact already exists, call `constant-contact-get-contact-list-member` with `email-address` to show which lists they are on. These tools can only add a list when creating a contact, so tell the user the existing contact must be added to the list in Constant Contact, and stop.
* If the contact's permission-to-send is unsubscribed, never re-add them.

**Step 3: Confirm consent and details**

Split `{full-name}` into first and last name. Ask the user how the contact gave permission: explicit only if they opted in directly (a signup form, a request to join), otherwise implicit. Show email, first name, last name, list name and permission. Do not proceed without an explicit yes.

**Step 4: Create**

Call `constant-contact-add-contact` exactly once with `email`, `first-name`, `last-name`, `list-id` and `permission-to-send`. Then call `constant-contact-get-contact-list-member` with `email-address` set to `{email-address}` and confirm the contact is on the list.

**Rules & Guidelines:**

* `constant-contact-add-contact` is the only write tool this prompt may call. Do not call `constant-contact-update-contact`, `constant-contact-add-contact-list` or `constant-contact-update-contact-list`. Do not create the list if it does not exist.
* Never mark permission as explicit unless the user states the contact opted in.

**Validation:**

* If `{email-address}` is not a valid email address, say so and stop.