fix(alembic): collapse ingestion_run + job_metadata heads to a single tip

Two issues blocked test_no_phantom_migrations after the previous
restoration:

1. e728126476a8 (add kb_id to ingestion_run) chained off
   15fe9304bca7 (creates knowledge_base) which left the
   ingestion_run-creation migration 72df732be86b dangling as its own
   head. Re-chain e728126476a8 onto 72df732be86b so the ingestion_run
   chain is linear; the FK target dependency on knowledge_base is
   declared via depends_on instead of down_revision.

2. After step 1 the graph still had two independent tips —
   16a290ab1332 (ingestion_run.user_metadata) and da7f6b9b638a
   (job.job_metadata) — neither referencing the other. Add an empty
   merge migration 5238aab36810 unifying both so 'alembic upgrade
   head' resolves to a single revision.

`alembic heads` now reports ['5238aab36810'] and
test_migration_execution passes locally (8 passed, 2 sqlite-only
skips).

Author: keval718

src/backend/base/langflow/alembic/versions/5238aab36810_merge_ingestion_run_metadata_and_job_metadata_heads.py

@@ -0,0 +1,42 @@
+"""Merge ingestion_run.user_metadata and job.job_metadata heads.
+
+Revision ID: 5238aab36810
+Revises: 16a290ab1332, da7f6b9b638a
+Create Date: 2026-04-30 20:30:00.000000
+
+Phase: MERGE
+Safe to rollback: YES — merge migrations are pure graph nodes; they
+    don't run any DDL.
+
+After the kb_id-on-ingestion_run change (``e728126476a8``) was rebased
+onto ``72df732be86b`` so the ``ingestion_run`` chain is linear, the
+graph still had two independent tips:
+
+* ``16a290ab1332`` — adds ``user_metadata`` JSON to ``ingestion_run``.
+* ``da7f6b9b638a`` — adds ``job_metadata`` JSON to ``job``.
+
+Neither references the other, so ``alembic upgrade head`` would
+``CommandError: Multiple head revisions are present``. This empty
+migration unifies them so future migrations can chain off a single
+head without picking sides between the KB ingestion-run and the
+job-metadata work.
+"""
+
+from collections.abc import Sequence
+
+# revision identifiers, used by Alembic.
+revision: str = "5238aab36810"  # pragma: allowlist secret
+down_revision: tuple[str, ...] | str | None = (
+    "16a290ab1332",  # pragma: allowlist secret
+    "da7f6b9b638a",  # pragma: allowlist secret
+)
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    """No-op merge — combines two parallel migration heads."""
+
+
+def downgrade() -> None:
+    """No-op merge — combines two parallel migration heads."""

src/backend/base/langflow/alembic/versions/e728126476a8_add_kb_id_to_ingestion_run.py

@@ -22,9 +22,14 @@
 
 # revision identifiers, used by Alembic.
 revision: str = "e728126476a8"  # pragma: allowlist secret
-down_revision: str | None = "15fe9304bca7"  # pragma: allowlist secret
+# Chain through ``72df732be86b`` (creates ingestion_run) so this
+# migration has only one parent path. The FK target ``knowledge_base``
+# table is a separate dependency declared via ``depends_on`` so the
+# graph stays valid no matter which order the unrelated KB-table
+# branch runs.
+down_revision: str | None = "72df732be86b"  # pragma: allowlist secret
 branch_labels: str | Sequence[str] | None = None
-depends_on: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = "15fe9304bca7"  # pragma: allowlist secret
 
 TABLE_NAME = "ingestion_run"
 COLUMN_NAME = "kb_id"