chore: import upstream snapshot with attribution

contributing/samples/context_management/migrate_session_db/sample-output/alembic/README

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+Generic single-database configuration.

contributing/samples/context_management/migrate_session_db/sample-output/alembic/env.py

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+# 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.
+
+from logging.config import fileConfig
+
+from alembic import context
+from sqlalchemy import engine_from_config
+from sqlalchemy import pool
+
+# this is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
+config = context.config
+
+# Interpret the config file for Python logging.
+# This line sets up loggers basically.
+if config.config_file_name is not None:
+  fileConfig(config.config_file_name)
+
+# add your model's MetaData object here
+# for 'autogenerate' support
+from google.adk.sessions.database_session_service import Base
+
+# target_metadata = mymodel.Base.metadata
+target_metadata = Base.metadata
+
+# other values from the config, defined by the needs of env.py,
+# can be acquired:
+# my_important_option = config.get_main_option("my_important_option")
+# ... etc.
+
+
+def run_migrations_offline() -> None:
+  """Run migrations in 'offline' mode.
+
+  This configures the context with just a URL
+  and not an Engine, though an Engine is acceptable
+  here as well.  By skipping the Engine creation
+  we don't even need a DBAPI to be available.
+
+  Calls to context.execute() here emit the given string to the
+  script output.
+
+  """
+  url = config.get_main_option("sqlalchemy.url")
+  context.configure(
+      url=url,
+      target_metadata=target_metadata,
+      literal_binds=True,
+      dialect_opts={"paramstyle": "named"},
+  )
+
+  with context.begin_transaction():
+    context.run_migrations()
+
+
+def run_migrations_online() -> None:
+  """Run migrations in 'online' mode.
+
+  In this scenario we need to create an Engine
+  and associate a connection with the context.
+
+  """
+  connectable = engine_from_config(
+      config.get_section(config.config_ini_section, {}),
+      prefix="sqlalchemy.",
+      poolclass=pool.NullPool,
+  )
+
+  with connectable.connect() as connection:
+    context.configure(connection=connection, target_metadata=target_metadata)
+
+    with context.begin_transaction():
+      context.run_migrations()
+
+
+if context.is_offline_mode():
+  run_migrations_offline()
+else:
+  run_migrations_online()

contributing/samples/context_management/migrate_session_db/sample-output/alembic/script.py.mako

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+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, Sequence[str], None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    ${downgrades if downgrades else "pass"}