diff --git a/backend/alembic/env.py b/backend/alembic/env.py
index 5610b382..a3b662d4 100644
--- a/backend/alembic/env.py
+++ b/backend/alembic/env.py
@@ -29,7 +29,6 @@ from app.models.session_branch import SessionBranch  # noqa: F401
 from app.models.fork_point import ForkPoint  # noqa: F401
 from app.models.session_handoff import SessionHandoff  # noqa: F401
 from app.models.session_resolution_output import SessionResolutionOutput  # noqa: F401
-import os
 
 from app.core.config import settings
 
@@ -38,21 +37,16 @@ def _alembic_sync_url() -> str:
     """Return a psycopg2-compatible sync URL for Alembic.
 
     Priority order:
-    1. Railway native PG env vars (PGHOST/PGPASSWORD/PGUSER/PGDATABASE) — these
-       are auto-linked per-environment by the Railway PostgreSQL service, so they
-       always carry the correct superuser credentials for the current environment
-       (production, PR preview, etc.), including fresh DBs with no custom roles yet.
+    1. DATABASE_URL_SYNC — in Railway this is set as a reference variable
+       (${{pgvector.DATABASE_URL}}) that resolves to the correct postgres
+       superuser credentials for the current environment (production, PR preview,
+       etc.). This always works even on fresh databases before any custom roles
+       have been created, because it uses the postgres superuser.
     2. ADMIN_DATABASE_URL (resolutionflow_admin, BYPASSRLS) converted to a sync
-       driver — used for local dev and stable environments where the role exists.
-    3. DATABASE_URL_SYNC — last resort / legacy fallback.
+       driver — fallback for local dev where DATABASE_URL_SYNC may not be set.
     """
-    pg_host = os.getenv("PGHOST")
-    pg_user = os.getenv("PGUSER")
-    pg_password = os.getenv("PGPASSWORD")
-    pg_db = os.getenv("PGDATABASE")
-    pg_port = os.getenv("PGPORT", "5432")
-    if all([pg_host, pg_user, pg_password, pg_db]):
-        return f"postgresql://{pg_user}:{pg_password}@{pg_host}:{pg_port}/{pg_db}"
+    if settings.DATABASE_URL_SYNC:
+        return settings.DATABASE_URL_SYNC
 
     admin_url = settings.ADMIN_DATABASE_URL
     if admin_url and "+asyncpg" in admin_url: