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_tamper_ledger.py

@@ -20,8 +20,7 @@ try:
     from cloud.cost import CostStore, dual_column_view, price_usd_micros
     from cloud.ledger import (
         GENESIS_HASH, LedgerStore, append_pushback_round,
-        audit_timeline, export_chain, list_pushback_rounds,
-        module_failure_counts, verify_chain, verify_export)
+        list_pushback_rounds, verify_export)
     from cloud.server import create_server, init_db
 except ImportError:  # discover -s cloud/tests 时把项目根目录补进 sys.path
     sys.path.insert(0, str(Path(__file__).resolve().parents[2]))
@@ -29,8 +28,8 @@ except ImportError:  # discover -s cloud/tests 时把项目根目录补进 sys.p
     from cloud.cost import CostStore, dual_column_view, price_usd_micros
     from cloud.ledger import (
         GENESIS_HASH, LedgerStore, append_pushback_round,
-        audit_timeline, export_chain, list_pushback_rounds,
-        module_failure_counts, verify_chain, verify_export)
+        list_pushback_rounds,
+        verify_export)
     from cloud.server import create_server, init_db
 
 
@@ -442,7 +441,7 @@ class TestTightenedCaliber(unittest.TestCase):
                 contract_refrozen=True)
 
     def test_meta_review_correction_changes_effective_count(self):
-        first = self._verdict("fail")
+        self._verdict("fail")
         self._verdict("fail")
         third = self._verdict("fail")
         self.assertEqual(