fix(rag): retain interrupted ingestion state and engine identity

src/langbot/pkg/persistence/alembic/versions/0025_rag_document_identity.py

@@ -0,0 +1,28 @@
+"""Persist engine document identity separately from the public Host file UUID."""
+
+from alembic import op
+import sqlalchemy as sa
+
+revision = '0025_rag_document_identity'
+down_revision = '0024_passkey_credentials'
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    inspector = sa.inspect(op.get_bind())
+    if 'knowledge_base_files' not in inspector.get_table_names():
+        return
+    columns = {column['name'] for column in inspector.get_columns('knowledge_base_files')}
+    if 'engine_document_id' not in columns:
+        # Legacy upstream IDs cannot be inferred from Host UUIDs or user config.
+        op.add_column('knowledge_base_files', sa.Column('engine_document_id', sa.Text(), nullable=True))
+
+
+def downgrade() -> None:
+    inspector = sa.inspect(op.get_bind())
+    if 'knowledge_base_files' not in inspector.get_table_names():
+        return
+    columns = {column['name'] for column in inspector.get_columns('knowledge_base_files')}
+    if 'engine_document_id' in columns:
+        op.drop_column('knowledge_base_files', 'engine_document_id')