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_chunking.py

@@ -171,7 +171,7 @@ def _assert_nothing_thin_and_nothing_lost(title: str, body: str) -> list[str]:
 
 
 def test_a_heading_over_one_long_paragraph_is_not_a_chunk_of_its_own():
-    """A work log whose entry is one long paragraph: the split used to flush
+    """A work log whose entry is one long paragraph: the split must not flush
     the heading as its own piece before cutting the paragraph."""
     entry = " ".join(["The deploy was verified against the live instance."] * 40)
     _assert_nothing_thin_and_nothing_lost(