docs(6209): preference door, systems and notes tools, lesson surfacing, rule versions, backup round trip, JSON reader, charter search, provenance, location filter

Ten more test files: issue, milestone, rule, decision and snippet numbers
come out of docstrings, comments and messages; the preference door states
what a preference is instead of quoting the framing; the JSON reader says
why jq is not assumed instead of what every hook used to do; the backup
round trip's column warning no longer claims the import side is unguarded.

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

tests/test_snippet_provenance.py

@@ -1,10 +1,10 @@
-"""Body provenance — the cache-with-provenance half of the pointer model (#2688).
+"""Body provenance — the cache-with-provenance half of the pointer model.
 
-Decision #2686: the recorded location is the source of truth for a snippet's
+The recorded location is the source of truth for a snippet's
 code and the stored body is a CACHE of it. `data.provenance` records what that
 cache is a cache OF — the commit the body was read at, and when — so staleness
-becomes judgeable instead of guessed, and so the forge fetch (milestone 288
-step 5) has something to refresh.
+becomes judgeable instead of guessed, and so the forge fetch has something to
+refresh.
 
 The rules under test, because each has a way to rot silently:
 
@@ -18,8 +18,8 @@ The rules under test, because each has a way to rot silently:
     cached body matches the source there.
 
 Unit tests cover the compose/carry logic; the integration section runs the
-same rules through the real service paths on real Postgres (the #2663 lesson —
-a DB-touching path with only mocked coverage is a path with no coverage).
+same rules through the real service paths on real Postgres (a DB-touching path
+with only mocked coverage is a path with no coverage).
 """
 import pytest
 import pytest_asyncio
@@ -49,7 +49,7 @@ def test_compose_provenance_stamps_sha_and_time():
 
 
 def test_compose_provenance_without_a_sha_is_none_not_an_empty_record():
-    # Absent provenance must stay ABSENT (the pre-#2688 semantics), never an
+    # Absent provenance must stay ABSENT, never an
     # empty dict that readers would have to distinguish from a real one.
     assert compose_provenance(commit_sha="") is None
     assert compose_provenance(commit_sha="   ") is None