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_frontend_request_deadlines.py

@@ -1,4 +1,4 @@
-"""Every request the web UI makes has a deadline (rule 156).
+"""Every request the web UI makes has a deadline.
 
 A source-inspection guard in the unit lane — there is no frontend test runner,
 and this is a property of the source rather than of a rendered result, so
@@ -7,7 +7,7 @@ reading the source is the honest way to check it.
 WHY. `fetch`'s default is to wait as long as the browser will. That is not a
 long timeout, it is the absence of one, and there is no state a surface can
 render for "pending forever" that is not a lie — the spinner that never
-resolves is indistinguishable from work still in progress. Rule 156 names
+resolves is indistinguishable from work still in progress. The practice names
 `fetch` specifically:
 
     When a library's default is "wait indefinitely" — `fetch`, most HTTP
@@ -67,17 +67,15 @@ def test_every_fetch_passes_a_signal():
         if "signal:" not in call
     ]
     assert not naked, (
-        "these fetch calls carry no AbortSignal, so they wait forever "
-        "(rule 156):\n  " + "\n  ".join(naked)
+        "these fetch calls carry no AbortSignal, so they wait forever:\n  " + "\n  ".join(naked)
     )
 
 
 def test_the_client_applies_its_deadline_by_default():
     """The specific regression that would silently undo this.
 
-    An earlier pass (#3329) made `timeoutMs` OPT-IN and used it at exactly one
-    call site, which left ~330 others waiting forever while the mechanism
-    looked present. Reverting to that shape would not fail the guard above —
+    An OPT-IN `timeoutMs` used at one call site leaves every other call
+    waiting forever while the mechanism looks present. That shape would not fail the guard above —
     every call would still reach `fetch` through `request()` — so the default
     is pinned here separately.
 
@@ -93,7 +91,7 @@ def test_the_client_applies_its_deadline_by_default():
 
 
 def test_a_timeout_arrives_as_the_error_shape_callers_already_handle():
-    """Rule 156's second half: expiry surfaces as a NAMED failure.
+    """The deadline's second half: expiry surfaces as a NAMED failure.
 
     A raw `DOMException: TimeoutError` reaches `apiErrorMessage(e, fallback)`
     as an object with no `body`, so every catch site in the app would print its