Allow progressive insight, and apply two to the bus record

A record can assert a fact that goes stale while the decision it supports
stays right. Superseding for that buries a sound record under a second one
and makes every reader work out which is live. So a correction of fact is
now made in place, marked and dated, with the old wording quoted — bounded
by three conditions and checked by records.py, which fires on an unmarked,
undated or back-dated note. Judgements still supersede.

Applied to 0115: no conformance suite exists to recapture, and the full
genesis bed cannot run until the links exist. Designs 25 and 28 follow.

00-META/process/02-graduation.md

@@ -33,7 +33,10 @@
 A design changes only through a decision.
 
 1. Write the decision record. If it reverses an earlier one, the earlier record's `status:`
-   becomes `superseded-by: 02-DECISIONS/NNNN-....md` — **its text is never edited**.
+   becomes `superseded-by: 02-DECISIONS/NNNN-....md` — **its reasoning is never rewritten**. If the
+   earlier record is sound and only a *fact* in it went stale, that is a **progressive insight**,
+   corrected in place and marked in the record rather than superseded
+   ([`02-DECISIONS/README.md`](../../02-DECISIONS/README.md)).
 2. Edit the to-be design document and set `updated:` to today.
 3. If the amendment came from an issue, set that issue's `amended-design:` to the document
    path.
@@ -54,4 +57,5 @@ Implementation state is a third axis, independent of both design and decision.
 
 - Do not move a to-be document into `00-as-is/`. Write the as-is document; both stand.
 - Do not edit an as-is document to describe an intention. That is what the to-be layer is for.
-- Do not change a decision record's meaning. Supersede it.
+- Do not change a decision record's meaning. Supersede it. Correcting a fact it got wrong, while
+  the decision stands, is a progressive insight — marked and dated in the record, never silent.