STAC-23211: Draft stackpack downgrade endpoint

Author: aacevedoosorio

spec/stackpack.xapi.yaml

@@ -169,6 +169,32 @@ paths:
                 type: string
         "500":
           $ref: "generic_error_handling.xapi.yaml#/components/responses/genericErrorsResponse"
+
+  /stackpack/{stackPackName}/downgrade:
+    post:
+      tags:
+        - stackpack
+      parameters:
+        - $ref: "#/components/parameters/stackPackName"
+        - $ref: "#/components/parameters/requiredStackPackVersion"
+        - in: query
+          name: unlocked
+          allowReserved: true
+          required: true
+          schema:
+            type: string
+      summary: "Downgrade API"
+      operationId: downgradeStackPack
+      description: "Downgrade a StackPack to an older version. Only supported for StackPacks 2.0; the target version must be lower than the currently installed version."
+      responses:
+        "200":
+          description: "successful"
+          content:
+            application/json:
+              schema:
+                type: string
+        "500":
+          $ref: "generic_error_handling.xapi.yaml#/components/responses/genericErrorsResponse"
   /stackpack/{stackPackName}/versions:
     get:
       tags:
@@ -340,6 +366,13 @@ components:
       schema:
         type: string
       description: "Optional version string (e.g. '1.2.3'). If not provided, the latest version is used. When provisioning, the StackPack cannot already be installed at a different version."
+    requiredStackPackVersion:
+      in: query
+      name: version
+      required: true
+      schema:
+        type: string
+      description: "Version string (e.g. '1.2.3') to downgrade to. Must be lower than the currently installed version."
     version:
       in: path
       name: version