fix Fabric authority import compatibility

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a053ff-1d6f-7fe2-ac1c-a6eb40a42a0c

migrations/versions/b5e6f7a8c9d0_fabric_snapshot_set_revision.py

@@ -0,0 +1,35 @@
+"""accept deterministic Fabric snapshot-set revisions
+
+Revision ID: b5e6f7a8c9d0
+Revises: a4d5e6f7b8c9
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = "b5e6f7a8c9d0"
+down_revision = "a4d5e6f7b8c9"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.alter_column(
+        "fabric_graph_imports",
+        "source_commit",
+        existing_type=sa.String(length=80),
+        type_=sa.String(length=255),
+        existing_nullable=True,
+    )
+
+
+def downgrade() -> None:
+    op.alter_column(
+        "fabric_graph_imports",
+        "source_commit",
+        existing_type=sa.String(length=255),
+        type_=sa.String(length=80),
+        existing_nullable=True,
+        postgresql_using="left(source_commit, 80)",
+    )