chore: import upstream snapshot with attribution

contributing/samples/context_management/postgres_session_service/compose.yml

@@ -0,0 +1,38 @@
+# Copyright 2026 Google LLC
+#
+# Licensed 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.
+
+# Docker Compose configuration for the postgres_session_service sample.
+#
+# This file defines a PostgreSQL service used to demonstrate ADK's
+# DatabaseSessionService with a persistent backend. It sets up a
+# postgres:16-alpine container with:
+# - Default credentials (user: postgres, password: postgres)
+# - A pre-created database named 'adk_sessions'
+# - Port 5432 exposed for local access
+# - A named volume 'postgres_data' for data persistence
+
+services:
+  postgres:
+    image: postgres:16-alpine
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
+      POSTGRES_DB: adk_sessions
+    ports:
+      - "5432:5432"
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+
+volumes:
+  postgres_data: