Evaluated the Open Knowledge Format (GoogleCloudPlatform/knowledge-catalog okf
v0.2, scaccogatto/okf-skills) as a replacement for our decision-record system and
rejected it: its conformance rules are deliberately permissive exactly where ours
are strict (broken links, unknown types and missing fields must all be tolerated;
`deprecated` points at no successor), and its stable identity is the file path,
which the breadcrumb rule tells agents not to trust.
Adopted two of its optional families instead, additively:
- `stale-after: YYYY-MM-DD` on the metadata line — marks a record asserting an
outside-world fact as due for re-confirmation. Absolute date, no TTL.
- `**Sources:**` in the metadata block — the evidence a record rests on, as
distinct from `Signals:` (recall keywords).
Neither is required; absence is never an error. A malformed `stale-after` is
blocking (it would silently never fire), but a past-due record is only a
non-blocking `::notice::` — going stale is the passage of time, not a defect in
whatever commit is under test. The catalog's new "Review due" section renders the
date only and never a clock-derived verdict, so it cannot drift `--check` red on a
calendar boundary with no commit touching the corpus.
No backfill: no existing record adopts either field here.
fixes#603