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_services_supersession.py

@@ -1,7 +1,7 @@
 """The supersession claim — who may make it, and what it refuses.
 
-Step 2 of #278. Ranking behaviour is step 3; this covers only recording and
-reading the relation.
+Ranking behaviour is in test_supersession_ranking.py; this covers only
+recording and reading the relation.
 
 The cycle tests are the ones worth reading. Under FLAT demotion a ring of
 records that supersede each other claims every member is obsolete, so all of
@@ -53,7 +53,7 @@ async def test_superseding_a_note_you_can_only_READ_is_refused_not_dropped():
 
     Demoting someone else's record out of their retrieval is damage that is
     invisible from the outside — the caller would believe it worked, and the
-    owner would have no symptom to trace. Rule #47.
+    owner would have no symptom to trace.
     """
     # writable for the superseder (id 1), not for the target (id 2)
     writable = AsyncMock(side_effect=lambda uid, nid: nid == 1)