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_lesson_insight_round_trip.py

@@ -1,4 +1,4 @@
-"""Reading a lesson's insight back and re-composing it returns the same body (#4272).
+"""Reading a lesson's insight back and re-composing it returns the same body.
 
 THE PROPERTY. `update_lesson` is field-wise: an edit that touches only
 `system_ids`, or only `what`, passes `insight=None`, and the service then
@@ -24,11 +24,9 @@ insight", the full trigger was prepended again, and the stored lesson gained
 (n-1) paragraphs per update — silently, compounding, and in the half of the
 document that does the retrieving.
 
-Measured on the one real row this damaged (lesson #4207, a three-paragraph
-trigger): the body grew by exactly 607 characters per edit — the length of
-paragraphs 2 and 3 with their separators — taking it from 1291 characters to
-7361 over ten edits, at which point the trigger appears eleven times and the
-insight is 17% of the record.
+On a three-paragraph trigger the body grows by the length of paragraphs 2 and
+3 with their separators on every edit — after ten edits the trigger appears
+eleven times and the insight is a sixth of the record.
 
 WHY A MARKER COULD NOT HAVE FIXED IT. There is no end-of-trigger marker in
 the body and adding one would not repair a row already written without it.
@@ -99,7 +97,7 @@ def _stored(trigger: str, insight: str, sources: list[int]):
     MagicMock auto-creates truthy and coerces to `1`. A no-sources shape then
     recomposes with `**Learned from:** #1` and the round trip fails for a
     reason that has nothing to do with the trigger. `fake_lesson` pins that
-    field to None — note #2109's point, which is why the fixture exists.
+    field to None, which is why the fixture exists.
     """
     title, body = lessons_svc.lesson_document(WHAT, trigger, insight, sources)
     data = lessons_svc.compose_data(WHAT, trigger, sources)
@@ -137,7 +135,7 @@ def test_an_edit_that_changes_nothing_changes_nothing(_name, trigger, insight, s
     # Reported as a size delta rather than left to a diff of two multi-kilobyte
     # strings: the failure this catches is duplication, and the number of
     # characters gained says which paragraph came back far faster than an
-    # equality dump does (rule 167 — a guard has to name what broke).
+    # equality dump does (a guard has to name what broke).
     assert (title, body) == (note.title, note.body), (
         f"a no-op edit rewrote the lesson: title {len(title) - len(note.title):+d} "
         f"chars, body {len(body) - len(note.body):+d} chars"