Cancel the right GoTo Webinar registration, once

**Objective:** Cancel the registration of `{email}` for the upcoming webinar `{webinar-name}`: exactly one registrant, after the user confirms.

**Step 1: Identify the webinar**

Call `goto-webinar-get-webinar` with webinar-name.contains set to `{webinar-name}`. If nothing matches, stop. If more than one distinct webinar key matches, list each with its name, date and webinar key, and ask which one. If the chosen webinar's date has already passed, stop and say that cancelling a past registration has no effect.

**Step 2: Find the registrant**

Call `goto-webinar-get-registrant` with the webinar key and email set to `{email}`. If nothing comes back, stop and say this person is not registered for the webinar. If more than one record comes back, list them and stop.

**Step 3: Get the organizer key**

`goto-webinar-delete-registrant` requires an organizer key. Use the organizer key from the webinar record if the result includes one; otherwise use `{organizer-key}`. If neither is available, stop and ask the user for it. Never guess it.

**Step 4: Confirm**

Show the user: the registrant's first name, last name, email, status and registration date, and the webinar name, date and start time. State that the cancellation cannot be undone and that the person would have to register again. Ask for an explicit yes.

**Step 5: Cancel**

After a yes, call `goto-webinar-delete-registrant` once, with the organizer key, the registrant-key from Step 2 and the webinar key.

**Step 6: Verify**

Call `goto-webinar-get-registrant` with the webinar key and email again. Report success if no record comes back; if the record is still there, report that the cancellation did not take effect.

**Rules & Guidelines:**

* `goto-webinar-delete-registrant` is the only write tool this prompt may call, once, for the one registrant confirmed in Step 4.
* Never call `goto-webinar-add-registrant`.
* Never cancel on a partial email match. The registrant must be matched on the exact email given.
* If the call fails, report the error as returned and stop. Do not retry.

**Validation:**

* If `{email}` is not an email address, ask for a valid one before calling any tool.
* If the user does not answer yes, stop without writing anything.