fixup! Give every mapped expansion a region and store its index as region_index

The state store stores the region index, and the object path is built from
it. For an ordinary or mapped task that equals the public map index, but for
an unmapped task inside a loop it is the iteration, so documenting the path
component as map_index would tell a custom backend author that loop passes
never appear in the path. Name it region_index in the state store docs, the
common.io backend docs, the provider.yaml description and the generated
provider info.

Author: ashb

airflow-core/docs/core-concepts/task-and-asset-state-store.rst

@@ -38,7 +38,7 @@ Task and Asset state store provide two key/value stores to persist data like a j
      - Default lifetime
      - Primary use case
    * - **Task state store**
-     - A single task Instance (``dag_id`` + ``run_id`` + ``task_id`` + ``region_id`` + ``map_index``)
+     - A single task Instance (``dag_id`` + ``run_id`` + ``task_id`` + ``region_id`` + ``region_index``)
      - Configurable retention; cleared on task success when ``clear_on_success = True``
      - Survive retries, track in-flight jobs, checkpoint progress within a run, resume progress from checkpoint set by a past run
    * - **Asset state store**

airflow-core/src/airflow/serialization/dag_version_diff.py

@@ -256,6 +256,7 @@
         "retries",
         "retry_delay",
         "retry_exponential_backoff",
+        "returns_dag_result",
         "run_as_user",
         "start_date",
         "start_from_trigger",

providers/common/io/docs/state_store_backend.rst

@@ -27,7 +27,7 @@ section to ``airflow.providers.common.io.state_store.backend.StateStoreObjectSto
 ``state_store_objectstorage_path`` to the desired base location. The connection id is obtained from the
 user part of the URL, e.g. ``state_store_objectstorage_path = s3://conn_id@mybucket/task-state/``.
 
-Task state is stored under ``<dag_id>/<run_id>/[region=<region_id>/]<task_id>/<map_index>/<key>`` and asset state under
+Task state is stored under ``<dag_id>/<run_id>/[region=<region_id>/]<task_id>/<region_index>/<key>`` and asset state under
 ``assets/<asset_identifier>/<key>`` beneath the configured base path.
 
 By default (``state_store_objectstorage_threshold = 0``) all serialized values are offloaded to object storage.
@@ -76,6 +76,6 @@ Using the local filesystem (useful for development)::
 
 .. note::
 
-  Task state paths are keyed on ``(dag_id, run_id, region_id, task_id, map_index)`` and are stable across
+  Task state paths are keyed on ``(dag_id, run_id, region_id, task_id, region_index)`` and are stable across
   task retries. This makes this backend suitable for operators that use
   :class:`~airflow.sdk.ResumableJobMixin` to reconnect to external jobs after a retry.

providers/common/io/provider.yaml

@@ -122,7 +122,7 @@ config:
         description: |
           Base path on object storage for the task/asset state store backend, in URL format.
           When set, StateStoreObjectStorageBackend will persist task and asset state under this
-          prefix, organized as <dag_id>/<run_id>/[region=<region_id>/]<task_id>/<map_index>/<key>
+          prefix, organized as <dag_id>/<run_id>/[region=<region_id>/]<task_id>/<region_index>/<key>
           for tasks and assets/<asset_identifier>/<key> for assets.
         version_added: 1.8.0
         type: string

providers/common/io/src/airflow/providers/common/io/get_provider_info.py

@@ -85,7 +85,7 @@ def get_provider_info():
                         "default": "",
                     },
                     "state_store_objectstorage_path": {
-                        "description": "Base path on object storage for the task/asset state store backend, in URL format.\nWhen set, StateStoreObjectStorageBackend will persist task and asset state under this\nprefix, organized as <dag_id>/<run_id>/[region=<region_id>/]<task_id>/<map_index>/<key>\nfor tasks and assets/<asset_identifier>/<key> for assets.\n",
+                        "description": "Base path on object storage for the task/asset state store backend, in URL format.\nWhen set, StateStoreObjectStorageBackend will persist task and asset state under this\nprefix, organized as <dag_id>/<run_id>/[region=<region_id>/]<task_id>/<region_index>/<key>\nfor tasks and assets/<asset_identifier>/<key> for assets.\n",
                         "version_added": "1.8.0",
                         "type": "string",
                         "example": "s3://conn_id@bucket/task-state/",