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_services_snippets.py

@@ -82,8 +82,8 @@ def test_parse_does_not_promote_a_caller_tag_to_language():
 
 
 def test_caller_tag_survives_an_update_round_trip_without_a_language():
-    # Regression: the tag used to be read back as the language, then dropped
-    # from the extra-tag set on re-compose — so it silently disappeared.
+    # A tag read back as the language would be dropped from the extra-tag set
+    # on re-compose — and silently disappear.
     tags = s.compose_tags("", ["auth"])
     fields = s.parse_snippet_fields("n — u", s.compose_body(code="x = 1"), tags)
     extra = [t for t in tags if t not in (s.SNIPPET_TAG, fields["language"])]