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.

AGENTS.md

@@ -52,8 +52,12 @@ vocabulary — *controller* (not "control plane"), *foundation* (not "substrate"
   docs (`layer`, `status`, `code`, `updated`), issue reports (`status`, `located-in`,
   `fixed-by`, `amended-design`) and decision records (`status`, `date`, `deciders`).
   Never create a central status file; cross-cutting views are generated from frontmatter.
-- **`02-DECISIONS/` records are immutable.** Supersede with a new record; never edit meaning. Fixing a
-  broken link or path is allowed.
+- **`02-DECISIONS/` records hold their meaning.** Supersede with a new record rather than rewriting
+  what was decided, the options weighed, or a consequence another record relies on. Fixing a broken
+  link or path is allowed, and so is a **progressive insight** — a correction of *fact* that leaves
+  the decision standing, made in place, marked and dated in the record's own words
+  ([`02-DECISIONS/README.md`](02-DECISIONS/README.md)). A fact going stale is not the decision going
+  wrong, and superseding a sound record for one buries it.
 - **Design docs are prose and diagrams only** — no code. A manifest field may be named; a
   manifest may not be pasted.
 - **Two layers, never mixed.** [`03-DESIGN/00-as-is/`](03-DESIGN/00-as-is/) describes the mesh