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_session_context_ledger.py

@@ -1,4 +1,4 @@
-"""The SessionStart hook clears the rule ledger exactly when context dies (#3749).
+"""The SessionStart hook clears the rule ledger exactly when context dies.
 
 WHY THIS EXISTS
 
@@ -109,28 +109,16 @@ def test_the_rules_ledger_survives_exactly_when_the_context_does(tmp_path):
 
 
 def test_the_note_ledgers_are_cleared_too_now_that_a_repeat_is_shown(tmp_path):
-    """The decision this test used to pin, reversed — and why it could be.
+    """The note ledgers are cleared on a compaction too.
 
-    It read: the note arms were deliberately left out of #3749, whether a
-    surfaced NOTE should come back after a compaction is a different question,
-    and a glob over `<sid>.*` would decide it by accident. That was right when
-    it was written, and the reason was the note arms' behaviour rather than the
-    note arms' nature: a note repeat was WITHHELD, so clearing their ledger
-    meant re-injecting whole menu lines the session had already been given.
-    Against that, leaving them was the cheaper mistake.
-
-    #4101 removed the premise. A note repeat is now rendered again with a
-    `seen` marker instead of dropped from the search, so the ledger no longer
-    decides whether a record is reachable — only whether its line says the
+    A note repeat is rendered again with a `seen` marker rather than dropped
+    from the search, so the ledger does not decide whether a record is
+    reachable — only whether its line says the
     session has met it before. Across a compaction that marker becomes a false
     statement: it tells a freshly-summarised session it has already seen a
     record that is nowhere in its context. Keeping the ledger buys nothing and
-    asserts something untrue.
-
-    Kept as a named test rather than deleted, because the roster it guards
-    moved to tests/test_session_ledger_clear.py and what is worth keeping HERE
-    is the record that the answer changed, with the reason attached — a
-    deleted test takes the old decision's reasoning with it.
+    asserts something untrue. The full roster is guarded in
+    tests/test_session_ledger_clear.py.
     """
     env = _env(tmp_path)
     sid = "sess-scope"