fix(ci): tell stale branches to pull latest staging on vacuous type-check runs

scripts/type_check_gate.py

@@ -627,7 +627,9 @@ def cmd_check(head: Mapping[str, int], base_ref: str) -> None:
         print(
             f"FAIL: basedpyright produced no errors, but {BUDGET_PATH.name} allows "
             f"up to ~{expected}. The type checker almost certainly crashed or emitted "
-            f"nothing; refusing to certify a vacuous run."
+            f"nothing; refusing to certify a vacuous run. This usually means this "
+            f"branch is missing type checker fixes from its base branch: pull the "
+            f"latest {DEFAULT_BASE.removeprefix('origin/')} and merge or rebase onto it."
         )
         raise SystemExit(1)
     if not over_ceiling(head, budget):

tests/test_litellm/test_type_check_gate.py

@@ -200,6 +200,16 @@ def test_genuine_zero_and_empty_budget_are_not_vacuous():
     )
 
 
+def test_vacuous_run_failure_tells_the_user_to_pull_latest_staging(capsys):
+    import pytest
+
+    with pytest.raises(SystemExit):
+        gate.cmd_check({}, gate.DEFAULT_BASE)
+    out = capsys.readouterr().out
+    assert "refusing to certify a vacuous run" in out
+    assert "pull the latest litellm_internal_staging and merge or rebase onto it" in out
+
+
 def test_update_ratchets_a_limit_down_by_what_the_branch_fixed():
     # A rule that dropped from 40 (branch point) to 30 (current) fixed 10, so its
     # limit of 100 falls to 90 -- the granted headroom (60) is preserved, not the