docs(6209): lesson links, design roles, version readout and endpoint, timestamp filters, settings defaults, opened ledger, surfaces

Eight more test files state their properties without issue, milestone and
rule numbers or dated regressions. The version tests describe what folding
the channel into the version breaks instead of the date it did; the surface
registry and settings-defaults tests state that floors move rather than
quoting the decision that made them move.

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

tests/test_version_endpoint.py

@@ -1,11 +1,9 @@
 """`/api/version` reports three values, and never folds them together.
 
-WHAT THIS IS ABOUT (rule 149). Until 2026-08-31 the endpoint returned
-`{"version": "main"}` — CI set `BUILD_VERSION` to the CHANNEL, so a running
-instance answered the question "which build are you?" with the name of a
-branch. The cost was concrete rather than theoretical: during #3244's live
-acceptance a deploy was behaving as though it held older code, and the one
-endpoint whose job is to settle that could not.
+WHAT THIS IS ABOUT. A CI that sets `BUILD_VERSION` to the CHANNEL makes a
+running instance answer "which build are you?" with the name of a branch — and
+when a deploy behaves as though it holds older code, the one endpoint whose job
+is to settle that cannot.
 
 The three values answer different questions and so cannot be one value:
 
@@ -78,7 +76,7 @@ def test_the_channel_is_never_inside_the_name():
     })
     assert NAME_RE.match(out["version"]), (
         f"the version name is {out['version']!r} — not YYYY.MM.DD.HHMM. A "
-        f"channel or branch name here is the 2026-08-31 bug returning."
+        f"channel or branch name here is the channel folded into the version."
     )
     assert "stable" not in out["version"]
 
@@ -120,7 +118,7 @@ def test_a_malformed_ordering_key_is_dropped_not_passed_through():
 
 def test_the_channel_is_reported_verbatim():
     """Never validated against an enum — a build claiming something
-    unexpected is better shown than dropped (rule 149)."""
+    unexpected is better shown than dropped."""
     out = _version_payload({"APP_VERSION": "dev", "APP_CHANNEL": "canary"})
     assert out["channel"] == "canary"
 
@@ -138,7 +136,7 @@ def test_ci_does_not_stamp_the_channel_as_the_version():
     for wrong in ('BUILD_VERSION="main"', 'BUILD_VERSION="dev"'):
         assert wrong not in text, (
             f"CI sets {wrong} — that is the channel in the version field, "
-            f"which is the 2026-08-31 regression."
+            f"folding the three values into one."
         )
 
 
@@ -168,7 +166,7 @@ def test_ci_passes_all_three_plus_the_commit():
 
 @pytest.mark.parametrize("commit_epoch,expected", [
     # Midnight, where a naive formatter drops the leading zeros and yields
-    # "2026.01.05.0" — rule 149 names this case specifically.
+    # "2026.01.05.0" — the case the padding exists for.
     (datetime(2026, 1, 5, 0, 0, tzinfo=timezone.utc), "2026.01.05.0000"),
     (datetime(2026, 1, 5, 0, 7, tzinfo=timezone.utc), "2026.01.05.0007"),
     (datetime(2026, 12, 31, 23, 59, tzinfo=timezone.utc), "2026.12.31.2359"),