Stop overselling when Shopify stock outruns Business Central

**Objective:** Compare the quantity Shopify shows as in stock for each variant with the inventory Business Central holds for the matching item, and report every difference larger than `{quantity-threshold}` (default 0). Limit the check to SKU `{sku}` when it is given.

**Step 1: Read Shopify stock**

Call `shopify-get-product-variant` with `sku` set to `{sku}` when it is given, otherwise with `max-records` 250. Keep `sku`, `title`, `product-id`, `inventory-quantity`, `inventory-policy` and `barcode`. Skip variants with no SKU and count them.

**Step 2: Read Business Central stock**

For each variant, call `business-central-get-item` with `item-number` set to the Shopify `sku`. If nothing comes back and the variant has a `barcode`, retry with `gtin` set to the barcode. Keep `item-number`, `description`, `type`, `inventory`, `quantity-on-sales-order`, `quantity-on-purchase-order` and `reorder-point`.

Ignore Business Central items whose `type` is not an inventory item (services and non-inventory items carry no stock) and list them separately. If no item is found, record the variant as missing from Business Central and continue.

**Step 3: Compare**

Difference = Shopify `inventory-quantity` minus Business Central `inventory`. Flag the variant when the absolute difference is greater than `{quantity-threshold}` (default 0).

**Step 4: Report**

A table of flagged variants: SKU, title, Shopify quantity, Business Central inventory, difference, Business Central quantity on sales order, quantity on purchase order. Put variants where Shopify shows more than Business Central first, since those risk overselling, then the rest.

Then list: variants missing from Business Central, non-inventory items, and variants whose Shopify `inventory-policy` allows selling when out of stock while Business Central inventory is 0 or less.

**Rules & Guidelines:**

* `shopify-get-product-variant` is on the shopify server. `business-central-get-item` is on the business-central server.
* Both figures are totals across all locations. Do not try to compare location by location.
* This prompt is read-only. Do NOT call `shopify-add-inventory-level`, `business-central-update-item` or any other create, add or update tool on either server.
* If the user names a Business Central company, pass it as `company` on every Business Central call.

**Validation:**

* If Shopify returns no variants, report that and stop.
* Business Central inventory is in the item's base unit of measure. If a variant looks like a pack (for example the title says 6-pack or case), say the difference may be a unit-of-measure difference rather than a stock error.