docs(6209): seventeen more test files — lesson shape and round trip, rule scope/moments/kind/surfacing, drift, deadlock race, backup, inception, backfill, claims, supersession, ledgers, family shapes

Docstrings and comments state the property and its reason in the present
tense. The session-context ledger test no longer describes the decision it
"used to pin"; the supersession tests state demote-not-filter without the
quote; one-row measurements become the general shape with their figures.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_integration_preference_drift.py

@@ -1,4 +1,4 @@
-"""Real-Postgres tests for the drift surface (milestone 399 step 5, #3895).
+"""Real-Postgres tests for the drift surface.
 
 WHY THIS EXISTS
 
@@ -20,8 +20,8 @@ subquery picking the newest version per rule, an ownership clause spanning two
 paths, and a write that has to leave the history longer than it found it. A
 stand-in session returns whatever the test handed it, so it could confirm none
 of those. `test_the_restore_is_recorded_as_an_edit` is the one that matters
-most: it is the whole basis for allowing a one-click revert here when
-milestone 323 refused one for rules, and if it were ever to pass while the
+most: it is the whole basis for allowing a one-click revert here when rules
+have none, and if it were ever to pass while the
 restore silently overwrote history, the carve-out would be indefensible.
 """
 import pytest
@@ -228,8 +228,8 @@ async def test_restoring_puts_the_old_wording_back(world):
 async def test_the_restore_is_recorded_as_an_edit(world):
     """THE ONE THAT MATTERS MOST — it is why this carve-out is defensible.
 
-    Milestone 323 refused a one-click restore for rules because "a silent
-    revert would erase the only record of why the rewrite happened". The
+    Rules have no one-click restore because a silent revert would erase the
+    only record of why the rewrite happened. The
     preference carve-out survives that objection only while nothing is
     erased: the restore goes through `update_rule`, so it takes its own
     snapshot and the history GAINS an entry.
@@ -262,7 +262,7 @@ async def test_the_restore_is_recorded_as_an_edit(world):
 
 
 async def test_a_rule_refuses_the_one_click_restore(world):
-    """Milestone 323 stands for rules, and the kind check is in the service
+    """Rules still have no restore, and the kind check is in the service
     rather than only in the route — so a caller reaching this directly cannot
     forget it."""
     await rulebooks_svc.update_rule(