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_attempt_hook.py

@@ -51,7 +51,6 @@ try:
         PG_MARKER_DDL,
         classify_dispatch,
         consume_platform_marker,
-        ensure_marker_table,
         mark_platform_rerun,
     )
     from cloud.attempt_ledger import (
@@ -72,7 +71,6 @@ except ImportError:
         PG_MARKER_DDL,
         classify_dispatch,
         consume_platform_marker,
-        ensure_marker_table,
         mark_platform_rerun,
     )
     from cloud.attempt_ledger import (