fix(sessions): use LONGTEXT for MySQL message storage

src/agents/extensions/memory/sqlalchemy_session.py

@@ -48,6 +48,7 @@
     text as sql_text,
     update,
 )
+from sqlalchemy.dialects.mysql import LONGTEXT
 from sqlalchemy.exc import IntegrityError, OperationalError
 from sqlalchemy.ext.asyncio import AsyncEngine, async_sessionmaker, create_async_engine
 
@@ -64,7 +65,12 @@
 
 
 class SQLAlchemySession(SessionABC):
-    """SQLAlchemy implementation of [`Session`][agents.memory.session.Session]."""
+    """SQLAlchemy implementation of [`Session`][agents.memory.session.Session].
+
+    Newly created MySQL and MariaDB message tables use LONGTEXT for serialized items.
+    Existing tables are not migrated; applications must widen their message_data column
+    to store items larger than the existing column's limit.
+    """
 
     _table_init_locks: ClassVar[dict[tuple[str, str, str], threading.Lock]] = {}
     _table_init_locks_guard: ClassVar[threading.Lock] = threading.Lock()
@@ -215,7 +221,11 @@ def __init__(
                 ForeignKey(f"{sessions_table}.session_id", ondelete="CASCADE"),
                 nullable=False,
             ),
-            Column("message_data", Text, nullable=False),
+            Column(
+                "message_data",
+                Text().with_variant(LONGTEXT(), "mysql", "mariadb"),
+                nullable=False,
+            ),
             Column(
                 "created_at",
                 TIMESTAMP(timezone=False),

tests/extensions/memory/test_sqlalchemy_session.py

@@ -18,7 +18,11 @@
     Summary,
 )
 from sqlalchemy import event, insert, select, text, update
+from sqlalchemy.dialects import mysql, postgresql, sqlite
+from sqlalchemy.dialects.mysql.mariadb import MariaDBDialect
+from sqlalchemy.engine import Dialect
 from sqlalchemy.ext.asyncio import AsyncEngine, create_async_engine
+from sqlalchemy.schema import CreateColumn
 from sqlalchemy.sql import Select
 
 pytest.importorskip("sqlalchemy")  # Skip tests if SQLAlchemy is not installed
@@ -108,6 +112,27 @@ async def test_sqlalchemy_session_direct_ops(agent: Agent):
     assert len(retrieved_after_clear) == 0
 
 
+@pytest.mark.parametrize(
+    ("dialect", "expected_type"),
+    [
+        pytest.param(mysql.dialect(), "LONGTEXT", id="mysql"),
+        pytest.param(MariaDBDialect(), "LONGTEXT", id="mariadb"),
+        pytest.param(postgresql.dialect(), "TEXT", id="postgresql"),
+        pytest.param(sqlite.dialect(), "TEXT", id="sqlite"),
+    ],
+)
+async def test_message_data_column_type(dialect: Dialect, expected_type: str):
+    """MySQL needs large text storage; other dialects retain the existing TEXT column."""
+    session = SQLAlchemySession.from_url("message_column", url=DB_URL)
+    try:
+        column = session._messages.c.message_data
+        assert str(CreateColumn(column).compile(dialect=dialect)) == (
+            f"message_data {expected_type} NOT NULL"
+        )
+    finally:
+        await session.engine.dispose()
+
+
 async def test_sqlalchemy_session_defaults_to_escaped_non_ascii_storage():
     """Default storage keeps the historical escaped non-ASCII JSON representation."""
     session = SQLAlchemySession.from_url("default_ascii_storage", url=DB_URL, create_tables=True)