docs(6209): snippets, rule embeddings, notes, ledger ageing and references, routes, reporting, handshake, lesson kind, request deadlines, contract-around-change, family models

Twelve more test files drop issue, milestone, rule, note, lesson and
snippet numbers and the dated or one-project figures that recorded how
each property was found; the docstrings state the property and why it
holds. The contract-around-the-change guard keeps the dict-key example as
the failure a signature-watcher misses.

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

tests/test_rule_ledger_ageing.py

@@ -1,13 +1,12 @@
-"""Entries in the rule exclusion ledger age out (#3751).
+"""Entries in the rule exclusion ledger age out.
 
 WHY THIS EXISTS
 
-#3749 clears the ledger when an EVENT destroys context — a compaction, a
-/clear. This covers the case with no event at all: a long session where a rule
-was named two hundred turns ago and has simply fallen out of attention. Same
-argument #3702 made about tiers (present in context and salient at the
-moment are different properties), applied to time instead. The tier itself is
-gone since milestone 394; the distinction it taught is what survives.
+The ledger is cleared when an EVENT destroys context — a compaction, a /clear.
+This covers the case with no event at all: a long session where a rule was
+named two hundred turns ago and has simply fallen out of attention. Present in
+context and salient at the moment are different properties, and time
+separates them as surely as a compaction does.
 
 WHAT IS PINNED, AND WHAT DELIBERATELY IS NOT
 
@@ -76,7 +75,7 @@ def _write_ledger(ledger: Path, entries: list[tuple[str, int | None]]) -> None:
 
 
 def test_an_old_entry_ages_out_and_a_recent_one_does_not(tmp_path):
-    """BOTH DIRECTIONS IN ONE ASSERTION (rule 167), because either half alone
+    """BOTH DIRECTIONS IN ONE ASSERTION, because either half alone
     passes against a broken implementation.
 
     A test that only checks the old id is gone passes against a helper that