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_ledger_references_not_silence.py

@@ -121,11 +121,11 @@ async def test_the_repeat_is_counted_not_reported_as_a_result():
 
 @pytest.mark.asyncio
 async def test_a_call_where_everything_was_already_seen_is_readable():
-    """The fact that could not be expressed before.
+    """A call where every hit was already seen is not a call nothing cleared.
 
-    Previously this call logged zero results with no suppression count, so it
-    was indistinguishable from a bar nothing cleared — and the operator tuning
-    that bar would have been reading the wrong number.
+    Logged as zero results with no suppression count, it would be
+    indistinguishable from a bar nothing cleared — and the operator tuning
+    that bar would be reading the wrong number.
     """
     rec = MagicMock()
     hits = [(0.80, fake_note(id=11, title="Pool sizing decision", user_id=1))]