add license.

Author: stankiewicz

.agent/skills/adding-new-metadata/SKILL.md

@@ -1,4 +1,21 @@
 ---
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
 name: adding-new-metadata
 description: Guide on how to add and propagate new metadata fields in Apache Beam's WindowedValue, extending protos, windmill persistence, and runner interfaces to avoid metadata loss.
 ---
@@ -40,14 +57,14 @@ For the Dataflow streaming runner, metadata must survive serialization to and fr
 
 *   **Serialization (Sink):**
     *   **File:** `runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/WindmillSink.java`
-    *   **Action:** Extract the metadata from the `WindowedValue`, and add it to already created ElementMetadata proto builder. 
+    *   **Action:** Extract the metadata from the `WindowedValue`, and add it to already created ElementMetadata proto builder.
 *   **Deserialization (Reader):**
     *   **Files:** `runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/UngroupedWindmillReader.java` and `WindowingWindmillReader.java`
     *   **Action:** Extract the metadata from ElementMetadata proto and reconstruct the `WindowedValue` using the updated factory methods/builders that include the metadata. This is incremental work, as plenty of metadata is already extracted from the proto.
 
 ## 4. Propagation Across Core Classes
 
-Metadata must be explicitly copied or forwarded whenever a `WindowedValue` is transformed, buffered, or processed
+Metadata must be explicitly copied or forwarded whenever a `WindowedValue` is transformed, buffered, or processed.
 
 ### DoFn Runners (Java Core)
 You must ensure that when a DoFn processes an element and outputs a new element, the appropriate metadata from the *input* is propagated to the *output* (unless explicitly changed by the logic).