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_shared_write_access.py

@@ -1,9 +1,9 @@
 """Editing a shared record: an editor grant is enough, a viewer grant is not.
 
-The agent and web paths used to disagree — and worse, within the agent path
-`delete_snippet` honoured editor shares while `update_snippet` did not, so a
-colleague's snippet could be destroyed through an agent but not improved. Both
-now resolve the read scope and then require WRITE, which is what the sharing UI
+The agent and web paths must agree, and so must the doors within one path: a
+`delete_snippet` that honours editor shares beside an `update_snippet` that
+does not lets a colleague's snippet be destroyed through an agent but not
+improved. Every door resolves the read scope and then requires WRITE, which is what the sharing UI
 already promises: viewer / editor / admin are distinct grants.
 
 A record readable-but-not-writable raises PermissionError rather than reporting