fix!: rename variant.selected_options → options (Universal-Commerce-Protocol#353) (Universal-Commerce-Protocol#356)

Completes a rename decided in PR Universal-Commerce-Protocol#195 (get_product operation) but never
  executed on variant.json. The get_product operation introduced three
  distinct concepts that were previously conflated:

    request.selected  — what the user chose (input parameter)
    product.selected  — what the server resolved (response, post-relaxation)
    variant.options   — what the variant IS (intrinsic, immutable)

  A variant's option values (Color: Blue, Size: Large) are intrinsic
  identity — they don't change based on user selections or server
  relaxation. The old name "selected_options" implied a relationship to
  user selection state that doesn't exist at the variant level.

  Schema: variant.selected_options → variant.options
  Docs: update variant examples in mcp.md and rest.md

Co-authored-by: Ilya Grigorik <ilya@grigorik.com>

Author: jingyli

docs/specification/catalog/mcp.md

@@ -214,7 +214,7 @@ Maps to the [Catalog Search](search.md) capability.
                   "description": { "plain": "Size 10 variant" },
                   "price": { "amount": 12000, "currency": "USD" },
                   "availability": { "available": true },
-                  "selected_options": [
+                  "options": [
                     { "name": "Size", "label": "10" }
                   ],
                   "tags": ["running", "road", "neutral"],
@@ -554,7 +554,7 @@ Maps to the [Catalog Lookup](lookup.md#get-product-get_product) capability. Retu
                 "description": { "plain": "Blue, Size 10" },
                 "price": { "amount": 12000, "currency": "USD" },
                 "availability": { "available": true },
-                "selected_options": [
+                "options": [
                   { "name": "Color", "label": "Blue" },
                   { "name": "Size", "label": "10" }
                 ]
@@ -566,7 +566,7 @@ Maps to the [Catalog Lookup](lookup.md#get-product-get_product) capability. Retu
                 "description": { "plain": "Blue, Size 12" },
                 "price": { "amount": 15000, "currency": "USD" },
                 "availability": { "available": true },
-                "selected_options": [
+                "options": [
                   { "name": "Color", "label": "Blue" },
                   { "name": "Size", "label": "12" }
                 ]

docs/specification/catalog/rest.md

@@ -152,7 +152,7 @@ Maps to the [Catalog Search](search.md) capability.
               "description": { "plain": "Size 10 variant" },
               "price": { "amount": 12000, "currency": "USD" },
               "availability": { "available": true },
-              "selected_options": [
+              "options": [
                 { "name": "Size", "label": "10" }
               ],
               "tags": ["running", "road", "neutral"],
@@ -428,7 +428,7 @@ on option values and returns variants matching the selection.
             "description": { "plain": "Blue, Size 10" },
             "price": { "amount": 12000, "currency": "USD" },
             "availability": { "available": true },
-            "selected_options": [
+            "options": [
               { "name": "Color", "label": "Blue" },
               { "name": "Size", "label": "10" }
             ]
@@ -440,7 +440,7 @@ on option values and returns variants matching the selection.
             "description": { "plain": "Blue, Size 12" },
             "price": { "amount": 15000, "currency": "USD" },
             "availability": { "available": true },
-            "selected_options": [
+            "options": [
               { "name": "Color", "label": "Blue" },
               { "name": "Size", "label": "12" }
             ]

source/schemas/shopping/types/variant.json

@@ -117,12 +117,12 @@
         }
       }
     },
-    "selected_options": {
+    "options": {
       "type": "array",
       "items": {
         "$ref": "selected_option.json"
       },
-      "description": "Option selections that define this variant."
+      "description": "Option values that define this variant (e.g., Color: Blue, Size: Large)."
     },
     "media": {
       "type": "array",