diff --git a/backend/app/models/event_chain.py b/backend/app/models/event_chain.py
index 4d0741f..7c5f077 100644
--- a/backend/app/models/event_chain.py
+++ b/backend/app/models/event_chain.py
@@ -5,7 +5,8 @@ class EventChain(Base):
     __tablename__ = "event_chains"
 
     event_id = Column(String, primary_key=True) # UUID string
-    session_id = Column(String(36), ForeignKey("sessions.session_id_str"), nullable=False, index=True)
+    session_id = Column(Integer, ForeignKey("sessions.id"), nullable=False, index=True)
+    session_id_str = Column(String(36), nullable=False)
     sequence_number = Column(Integer, nullable=False)
     timestamp_wall = Column(DateTime, nullable=False)
     timestamp_monotonic = Column(Float, nullable=True)
diff --git a/backend/app/models/session.py b/backend/app/models/session.py
index 8d55540..81b2551 100644
--- a/backend/app/models/session.py
+++ b/backend/app/models/session.py
@@ -1,8 +1,10 @@
-from sqlalchemy import Column, Integer, String, DateTime, ForeignKey
+from sqlalchemy import Column, Integer, String, DateTime, ForeignKey, Boolean
 from sqlalchemy.orm import relationship
 from sqlalchemy.sql import func
 from app.database import Base
 
+from sqlalchemy.sql import expression
+
 class Session(Base):
     __tablename__ = "sessions"
 
@@ -20,3 +22,4 @@ class Session(Base):
     # Relationships
     user = relationship("User", back_populates="sessions")
     events = relationship("Event", back_populates="session", cascade="all, delete-orphan")
+    is_replay = Column(Boolean, default=False, nullable=False, server_default=expression.false())