Record vendor credits accurately, and only once

**Objective:** Create a draft purchase credit memo against posted purchase invoice `{invoice-number}` for `{what-to-credit}` (default the whole invoice), with the vendor's credit memo number `{vendor-credit-memo-number}` if known.

Pass `{company}` as the company argument on every call. If `{company}` is empty, leave the company argument out so the connector's default company is used.

**Step 1: Read the invoice**

Call `business-central-get-posted-purchase-invoice` with invoice-number set to `{invoice-number}`; if nothing comes back try vendor-invoice-number. Stop if not found. Call `business-central-get-posted-purchase-invoice-line` with invoice-number.

**Step 2: Already credited**

Call `business-central-get-posted-purchase-credit-memo` with buy-from-vendor-number and keep those whose applies-to-document-number is this invoice; call `business-central-get-posted-purchase-credit-memo-line` for their lines. Call `business-central-get-purchase-transaction` with buy-from-vendor-number and document-type Credit Memo for drafts. Never credit more than invoiced minus already credited. If `{vendor-credit-memo-number}` is given, call `business-central-get-posted-purchase-credit-memo` with vendor-credit-memo-number set to it; a hit means it was already entered.

**Step 3: Preview and confirm**

Show the invoice lines, amounts already credited, and the proposed credit lines with the total. If a draft already exists, offer to amend it with `business-central-update-purchase-credit-memo-line` (sequence = line-number from `business-central-get-purchase-transaction-line`). Ask for confirmation.

**Step 4: Create**

After confirmation call `business-central-create-purchase-credit-memo` once with vendor-number and pay-to-vendor-number from the invoice, invoice-number, credit-memo-date today, and vendor-credit-memo-number when given. Then call `business-central-create-purchase-credit-memo-line` per line with document-number, line-type, number-on-line, quantity and unit-cost.

**Step 5: Confirm the result**

Re-read with `business-central-get-purchase-transaction` and `business-central-get-purchase-transaction-line`. Report the number and total. Use `business-central-update-purchase-credit-memo` only if the vendor's credit memo number arrives later, after confirmation.

**Rules & Guidelines:**

* Do not call any create or update tool until the user has confirmed the exact values shown in the preview.
* Call `business-central-create-purchase-credit-memo` at most once.

**Validation:**

* If the invoice is fully credited already, say so and stop.