code-to10 v6 A14 batch2: test E402/F401 cleanup plus touched-file residual E,F cleanup

(cherry picked from commit 1db02545f74c96b3b92be4fc32954659cec1f814)

Reconcile-conflict: A14b E402 imports referencing cloud.handler_core (does not exist here; core methods live in server.py) — kept HEAD imports with incoming's noqa: E402 markers, dropped the unused core_mod import (verified unused elsewhere in both files).

cloud/tests/test_v2cov_gaps_b1.py

@@ -27,8 +27,8 @@ from unittest import mock
 REPO_ROOT = Path(__file__).resolve().parents[2]
 sys.path.insert(0, str(REPO_ROOT))
 
-from cloud.server import init_db
-from cloud.worker import Worker, _code_signature
+from cloud.server import init_db  # noqa: E402
+from cloud.worker import Worker, _code_signature  # noqa: E402
 
 FAKE_ENV = {"XCM_API_KEY": "test-placeholder"}
 
@@ -155,7 +155,6 @@ class StepAndCheckpointTestCase(_Base):
 
     def test_checkpoint_mirror_loop_exception_swallowed(self):
         w = _worker(self.db_path)
-        calls = []
         w._mirror_checkpoint_once = lambda task: (_ for _ in ()).throw(
             RuntimeError("mirror down"))
         class _Stop: