XCom.get_value() via SDK fails in extra link plugin with SUPERVISOR_COMMS ImportError

### Apache Airflow version 3.1.3 ### If "Other Airflow 2/3 version" selected, which one? _No response_ ### What happened? When using XCom.get_value from the Task SDK / compat SDK inside an extra link plugin, the Airflow webserver/API fails with: `ImportError: cannot import name 'SUPERVISOR_COMMS' from 'airflow.sdk.execution_time.task_runner'` This happens when the UI calls the /api/v2/.../links endpoint to resolve extra links for a task instance. The same plugin works fine without the XCom.get_value(...) call (links render correctly). The problem only appears as soon as XCom.get_value is used in the BaseOperatorLink.get_link() implementation. This looks like a bug / unsupported usage path where the Task SDK assumes it is running in a task runner context (with SUPERVISOR_COMMS) even though extra links are resolved in the API server / webserver context. ### What you think should happen instead? Using XCom.get_value(key="data_doc", ti_key=ti_key) inside BaseOperatorLink.get_link() shouldn’t crash the /api/v2/.../links endpoint. <img width="2120" height="420" alt="Image" src="https://github.com/user-attachments/assets/8ebc2138-a9c2-4ca1-8986-8311361dd040" /> If there is no XCom row, I’d expect None or similar; the extra link should either: • return None/empty and be hidden, or • return the URL string and render normally. ### How to reproduce 1. Add the plugin file above to $AIRFLOW_HOME/plugins (or the Astro project plugins/ directory). ``` from airflow.providers.common.compat.sdk import BaseOperator, BaseOperatorLink, XCom from airflow.models.taskinstancekey import TaskInstanceKey from airflow.plugins_manager import AirflowPlugin from airflow.providers.standard.operators.python import PythonOperator class RerunTask(BaseOperatorLink): name = "Rerun Task" def get_link(self, operator: BaseOperator, *, ti_key: TaskInstanceKey): azure_url_code = XCom.get_value(key="data_doc", ti_key=ti_key) return "https://www.astronomer.io/" class PythonOperatorL…