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_rule_kind.py

@@ -1,6 +1,6 @@
-"""Real-Postgres tests for `rules.kind` and its CHECK (0098, #3849 step 1).
+"""Real-Postgres tests for `rules.kind` and its CHECK (migration 0098).
 
-Rule 36 exists because a value and its constraint drift apart: the code
+A value and its constraint drift apart: the code
 starts writing a new kind while the database still refuses it, and nothing
 catches it until a write fails in front of someone. A mock cannot show that —
 it has no CHECK — so the constraint gets a real-DB test, exactly as 0091's
@@ -94,8 +94,7 @@ async def test_an_unknown_kind_is_refused(topic_id):
     """The half that proves the constraint is there at all.
 
     Without this, every other assertion in this file would pass against a
-    table whose CHECK had been dropped — the exact failure rule 36 is written
-    against.
+    table whose CHECK had been dropped — the exact drift this guards.
     """
     _uid, topic = topic_id
     with pytest.raises(IntegrityError):
@@ -119,8 +118,8 @@ async def test_a_rule_can_become_a_preference_after_the_fact(topic_id):
     """The read-back is the whole test.
 
     A version asserting only that the update call succeeded would pass against
-    code that accepted `kind` and dropped it — which is how the same bug
-    survived on `task_kind` long enough to be found by hand (#3129).
+    code that accepted `kind` and dropped it — a bug that otherwise surfaces
+    only when someone finds it by hand.
 
     This is also the migration path the always-on triage needs: the rules that
     turn out to be preferences change one column and keep their id, history