feat(requires): support variable references in enum constraints (#2678)

website/src/docs/reference/schema.md

@@ -674,14 +674,12 @@ tasks:
 
 ```yaml
 tasks:
-  # Simple requirements
   deploy:
     requires:
       vars: [API_KEY, ENVIRONMENT]
     cmds:
       - ./deploy.sh
 
-  # Requirements with enum validation
   advanced-deploy:
     requires:
       vars:
@@ -693,6 +691,17 @@ tasks:
     cmds:
       - echo "Deploying to {{.ENVIRONMENT}} with log level {{.LOG_LEVEL}}"
       - ./deploy.sh
+
+
+  # Requirements with enum from variable reference
+  reusable-deploy:
+    requires:
+      vars:
+        - name: ENVIRONMENT
+          enum:
+            ref: .ALLOWED_ENVS
+    cmds:
+      - ./deploy.sh
 ```
 
 See [Prompting for missing variables interactively](/docs/guide#prompting-for-missing-variables-interactively)