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_milestone_summary_brief.py

@@ -134,7 +134,7 @@ async def _enter(*stubs):
 async def test_enter_project_stays_small_however_large_the_project():
     """The ceiling is the point: a long-lived project's handshake must not
     grow with its history. 200 milestones with 5k-character plans, 60 project
-    rules and 40 Systems would be well over 1M characters in the old shape."""
+    rules and 40 Systems would be well over 1M characters carried whole."""
     project = fake_project(id=5, design_system_id=9, goal=GOAL,
                            description="Background. " * 300)
     rules = {