fix(auth): fail closed when the adminAuth roles join errors (stable) (#975)

Closes #968 on stable. Backport of #974.

The roles-join fallback in adminAuth fabricated role_name='super_admin' on ANY database error, so a transient fault silently granted super_admin for its duration. Gate it on isMissingRolesSchema(), moved to utils/dbErrors.js and shared with apiTokenAuth, with the predicate tightened to trust SQLSTATE 42P01/42703 on Postgres and exact driver phrasing on SQLite.

backend/src/utils/dbErrors.js

@@ -12,4 +12,37 @@ function isUniqueViolation(err) {
   return /unique/i.test(msg) || /sqlite_constraint/i.test(msg);
 }
 
-module.exports = { isUniqueViolation };
+/**
+ * Does this error mean the `roles` table/column genuinely isn't there yet
+ * (mid-upgrade), as opposed to the database being briefly unhappy?
+ *
+ * The distinction matters because both auth paths fall back to granting
+ * super_admin when the roles join fails: a catch-all would turn any transient
+ * failure — connection reset, deadlock, statement timeout, pool exhaustion —
+ * into a privilege escalation that hands a demoted viewer exactly the access
+ * GHSA-9697 closes. Callers must rethrow anything this returns false for.
+ */
+function isMissingRolesSchema(err) {
+  if (!err) return false;
+  const message = String(err.message || '');
+
+  // Postgres is authoritative via SQLSTATE: 42P01 undefined_table, 42703
+  // undefined_column. Both are schema conditions, never transient.
+  if (err.code === '42P01' || err.code === '42703') return true;
+
+  // SQLite carries no SQLSTATE, so the driver's wording is all there is — but
+  // it must be matched EXACTLY, naming the object the roles join needs. A
+  // generic /does not exist/ test would be unsound here: knex prefixes the
+  // failing SQL to err.message, and that SQL always names `roles` on this
+  // join, so any "... does not exist" fault on the connection (e.g. pgbouncer
+  // losing a named prepared statement, SQLSTATE 26000) would read as a missing
+  // roles schema and fabricate super_admin.
+  //
+  // Two states are legitimate, per the migration order:
+  //   pre-054           → roles table absent
+  //   post-054, pre-057 → roles exists, admin_users.role_id not added yet
+  return /no such table: roles\b/i.test(message)
+    || /no such column: (roles\.|admin_users\.role_id\b)/i.test(message);
+}
+
+module.exports = { isUniqueViolation, isMissingRolesSchema };