docs(6209): test prose in the present tense — "used to", "previously", "before this" restated as the failure shape

Twenty-eight test files described the code they guard by what it did
before a fix. Each is now the property and the failure it prevents, in the
present tense: the backfill snapshot, the per-dial calibration query, the
rule scope, the lesson trigger filter, the subshell global, the trash owner
scope, the version readout fallback, and others. A docstring line that
narrated the backup suite's own history is removed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_calibration_stamp.py

@@ -195,8 +195,8 @@ async def test_a_dial_is_read_per_dial_not_from_the_newest_two_rows():
 
     "The newest two rows" and "the newest row of each dial" differ the moment
     one dial moves more often than the other — which is the normal case, since
-    floors get walked and budgets rarely do. Before this was one query per dial,
-    a surface with three floor changes and one budget change reported the budget
+    floors get walked and budgets rarely do. Without a query per dial, a
+    surface with three floor changes and one budget change reports the budget
     as untouched: a WRONG calibration answer rather than a missing one, and
     wrong in the direction a reader would not think to check.
     """