Declare X-Stock-Change-Reason as a proper header parameter

The tool argument name Kong actually forwards comes from the operation's
declared parameters — a header cannot be sent as an arbitrary argument name,
it has to be in the spec like any other parameter.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

kong/mcp/ai-mcp-proxy.yaml

@@ -288,7 +288,8 @@ config:
       idempotent_hint: false
       destructive_hint: false
       open_world_hint: false
-    description: Update specific fields of an existing product.
+    description: Update specific fields of an existing product. Send X-Stock-Change-Reason as delivery:<id>
+      when a quantityinstock change is a fulfilled reorder rather than a correction.
     method: PATCH
     name: patch-product
     parameters:
@@ -298,6 +299,13 @@ config:
       required: true
       schema:
         type: string
+    - description: 'Only honoured in this one shape: delivery:<reorder-id>. Anything else is recorded
+        as a manual adjustment.'
+      in: header
+      name: X-Stock-Change-Reason
+      required: false
+      schema:
+        type: string
     path: /catalog/v1/products/{productcode}/
     request_body:
       content: