Credit customers accurately, never beyond what was billed

**Objective:** Create a draft sales credit memo against posted invoice `{invoice-number}` for `{what-to-credit}` (default every line in full), for the reason `{reason}`.

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-sales-invoice` with invoice-number set to `{invoice-number}`. If nothing comes back, stop. Call `business-central-get-posted-sales-invoice-line` with invoice-number for its lines.

**Step 2: Check what is already credited**

Call `business-central-get-posted-sales-credit-memo` with sell-to-customer-number and keep those whose applies-to-document-number is this invoice. Call `business-central-get-posted-sales-credit-memo-line` for each to see which items and quantities were already credited. Call `business-central-get-sales-transaction` with sell-to-customer-number and document-type Credit Memo for drafts not posted yet. Never credit more than invoiced minus already credited on any line.

**Step 3: Work out the lines**

Map `{what-to-credit}` onto the invoice lines: whole lines, reduced quantities, or a price allowance. Use the invoice's unit-price for each line.

**Step 4: Preview and confirm**

Show the invoice, what was invoiced, what was already credited, and the proposed credit lines with the total. If a draft credit memo already exists for this invoice, say so and offer to amend it instead (with `business-central-update-sales-credit-memo-line`, using the line-number from `business-central-get-sales-transaction-line` as sequence). Ask for confirmation.

**Step 5: Create**

After confirmation call `business-central-create-sales-credit-memo` once with customer-number and bill-to-customer-number from the invoice, invoice-number `{invoice-number}`, and credit-memo-date today. Then call `business-central-create-sales-credit-memo-line` for each line with document-number, line-type, number-on-line, quantity, unit-price, and a description that includes `{reason}` on the first line.

**Step 6: Confirm the result**

Call `business-central-get-sales-transaction` and `business-central-get-sales-transaction-line` with the new document-number. Report the credit memo number and total, and that it must be posted in Business Central.

**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-sales-credit-memo` at most once. Use `business-central-update-sales-credit-memo` only to correct a draft's dates or references.

**Validation:**

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