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_contract_around_the_change.py

@@ -1,16 +1,14 @@
-"""You altered the shape of something — here is everything that reads it (#4215).
+"""You altered the shape of something — here is everything that reads it.
 
 WHY THIS EXISTS
 
-Milestone 419's most repeated miss, five of seven: acting on the thing in hand
-without reading the contract around it. Lesson #4207 says it in words —
-"widening a tuple is an interface change to every unpack site, and the
-compiler will not tell you" — and was written by its author HOURS before a
-structurally identical mistake, having been surfaced twice in the turns
-between. Text delivered at the moment of acting is too weak a carrier for a
-reflex that has to change what the act IS. This looks it up instead.
+The commonest miss is acting on the thing in hand without reading the contract
+around it: "widening a tuple is an interface change to every unpack site, and
+the compiler will not tell you". Knowing that in words does not stop it — text
+delivered at the moment of acting is too weak a carrier for a reflex that has
+to change what the act IS. This looks it up instead.
 
-Rule 33 one scope down: its checks are between layers ("every parameter the
+Layer parity one scope down: its checks are between layers ("every parameter the
 caller sends is read by the handler under the same name"), and the same
 question exists between a definition and its callers.
 
@@ -21,18 +19,17 @@ nothing alike in source:
     arg   its parameter names          arity and order
     key   quoted keys of dict literals the shape of what it RETURNS
 
-The third is here because of the miss that produced this step, and it is the
-one a signature-watcher would have missed: `get_writepath_config` gained one
-dict key, three arms read that dict inside a fail-open `except`, every one
-silently became a no-op, and ten tests went red at once with nothing pointing
-at the cause. No signature changed.
+The third is the one a signature-watcher misses: a function gains one dict
+key, three callers read that dict inside a fail-open `except`, every one
+silently becomes a no-op, and tests go red at once with nothing pointing at
+the cause. No signature changed.
 
 WHAT IS PINNED: which edits speak and which stay silent, and that both gates
 are load-bearing. NOT pinned: the wording, which is prose.
 
 A FIXTURE REPO, NEVER THIS ONE. Asserting against Scribe's own files would
 make the test a description of today's tree, failing the next time someone
-renames something (rule 115's reasoning, one floor down).
+renames something.
 """
 import subprocess
 from pathlib import Path