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_scribe_marker.py

@@ -119,13 +119,13 @@ def test_an_unusable_marker_is_refused_rather_than_sent(tmp_path, body):
 
 
 def test_the_reason_survives_the_command_substitution_that_fetches_it(tmp_path):
-    """Regression on a bug this nearly shipped with.
+    """The reason cannot be a global the function sets.
 
-    The reason used to be a global the function set, which every caller reads
-    through `$( )` — a subshell, so the assignment died with it and the caller
-    saw an UNSET variable. The hooks all run `set -u`, where reading one aborts
-    the script: a directory with a misaddressed marker would have cost the
-    session its entire SessionStart context, to fetch a warning about a file.
+    Every caller reads the function through `$( )` — a subshell, so a global
+    assignment dies with it and the caller sees an UNSET variable. The hooks all
+    run `set -u`, where reading one aborts the script: a directory with a
+    misaddressed marker would cost the session its entire SessionStart context,
+    to fetch a warning about a file.
 
     So the reason comes back through stdout with the id, and this asserts on
     the shape the caller actually uses: read in a subshell, split, and used