refactor: backup soft-deleted conversations instead of deleting them

- Create backup table conversations_4f02b6704509_bak for soft-deleted records
- Only create backup table if soft-deleted records exist
- Support recovery during downgrade migration
- Drop backup table after successful restoration

api/migrations/versions/2025_09_02_2012-4f02b6704509_remove_unused_is_deleted_field_from_.py

@@ -19,7 +19,21 @@ depends_on = None
 
 def upgrade():
     # ### commands auto generated by Alembic - please adjust! ###
-    # Delete any conversations where is_deleted is true before dropping the column
+    # Create backup table for soft-deleted conversations
+    backup_table_name = 'conversations_4f02b6704509_bak'
+    
+    # Check if there are any soft-deleted conversations
+    result = op.get_bind().execute(sa.text("SELECT COUNT(*) FROM conversations WHERE is_deleted = true"))
+    count = result.scalar()
+    
+    if count > 0:
+        # Create backup table with all columns from conversations
+        op.execute(sa.text(f"""
+            CREATE TABLE {backup_table_name} AS
+            SELECT * FROM conversations WHERE is_deleted = true
+        """))
+    
+    # Delete soft-deleted conversations from main table
     op.execute("DELETE FROM conversations WHERE is_deleted = true")
     
     with op.batch_alter_table('conversations', schema=None) as batch_op:
@@ -32,5 +46,26 @@ def downgrade():
     # ### commands auto generated by Alembic - please adjust! ###
     with op.batch_alter_table('conversations', schema=None) as batch_op:
         batch_op.add_column(sa.Column('is_deleted', sa.BOOLEAN(), server_default=sa.text('false'), autoincrement=False, nullable=False))
+    
+    # Restore soft-deleted conversations from backup table if it exists
+    backup_table_name = 'conversations_4f02b6704509_bak'
+    
+    # Check if backup table exists
+    result = op.get_bind().execute(sa.text(f"""
+        SELECT EXISTS (
+            SELECT FROM information_schema.tables 
+            WHERE table_name = '{backup_table_name}'
+        )
+    """))
+    
+    if result.scalar():
+        # Restore the soft-deleted conversations
+        op.execute(sa.text(f"""
+            INSERT INTO conversations 
+            SELECT * FROM {backup_table_name}
+        """))
+        
+        # Drop the backup table after restoration
+        op.execute(sa.text(f"DROP TABLE {backup_table_name}"))
 
     # ### end Alembic commands ###