chore(migration): Add the warning comments.

Signed-off-by: -LAN- <laipz8200@outlook.com>

api/migrations/versions/2025_06_19_1633-0ab65e1cc7fa_remove_sequence_number_from_workflow_.py

@@ -29,12 +29,21 @@ def upgrade():
 def downgrade():
     # ### commands auto generated by Alembic - please adjust! ###
 
+    # WARNING: This downgrade CANNOT recover the original sequence_number values!
+    # The original sequence numbers are permanently lost after the upgrade.
+    # This downgrade will regenerate sequence numbers based on created_at order,
+    # which may result in different values than the original sequence numbers.
+    #
+    # If you need to preserve original sequence numbers, use the alternative
+    # migration approach that creates a backup table before removal.
+
     # Step 1: Add sequence_number column as nullable first
     with op.batch_alter_table('workflow_runs', schema=None) as batch_op:
         batch_op.add_column(sa.Column('sequence_number', sa.INTEGER(), autoincrement=False, nullable=True))
 
     # Step 2: Populate sequence_number values based on created_at order within each app
-    # This recreates the original sequence numbering logic
+    # NOTE: This recreates sequence numbering logic but values will be different
+    # from the original sequence numbers that were removed in the upgrade
     connection = op.get_bind()
     connection.execute(sa.text("""
         UPDATE workflow_runs