feat: Set SqlAlchemy to fetch sequence_id from DB, not generate it itself (#1726)

letta/orm/message.py

@@ -1,7 +1,7 @@
 from typing import List, Optional
 
 from openai.types.chat.chat_completion_message_tool_call import ChatCompletionMessageToolCall as OpenAIToolCall
-from sqlalchemy import BigInteger, ForeignKey, Index, Sequence, event, text
+from sqlalchemy import BigInteger, FetchedValue, ForeignKey, Index, Sequence, event, text
 from sqlalchemy.orm import Mapped, Session, mapped_column, relationship
 
 from letta.orm.custom_columns import MessageContentColumn, ToolCallColumn, ToolReturnColumn
@@ -46,7 +46,13 @@ class Message(SqlalchemyBase, OrganizationMixin, AgentMixin):
     )
 
     # Monotonically increasing sequence for efficient/correct listing
-    sequence_id = mapped_column(BigInteger, Sequence("message_seq_id"), unique=True, nullable=False)
+    sequence_id: Mapped[int] = mapped_column(
+        BigInteger,
+        Sequence("message_seq_id"),
+        server_default=FetchedValue(),
+        unique=True,
+        nullable=False,
+    )
 
     # Relationships
     agent: Mapped["Agent"] = relationship("Agent", back_populates="messages", lazy="selectin")