diff --git a/knowledge/AUTHORING.md b/knowledge/AUTHORING.md
index fdfc493..adff0ec 100644
--- a/knowledge/AUTHORING.md
+++ b/knowledge/AUTHORING.md
@@ -44,7 +44,13 @@ Before approving new or materially changed Standing Knowledge:
    exact-candidate Founder Decision contract; Authority effect never lowers the
    receipt standard.
 7. Run the mechanical checks and review the exact Git diff.
-8. In an Instance, confirm the exact change carries the Founder ruling required
+8. Confirm each invariant the change adds or amends is **enforced or
+   advisory**: it names the check that fails when it stops being true — a
+   doctor rule, a CI check, or a per-process Check — or the rule itself states
+   that it is guidance. A rule with no checker decays
+   ([enforcement](docs/enforcement.md#a-rule-with-no-checker-decays)); a
+   checker whose failures are routinely ignored is the same defect.
+9. In an Instance, confirm the exact change carries the Founder ruling required
    by `ORG.md` and `AUTHORITY.md`. In the Seed source, confirm the branch or
    pull request received the repository's required maintainer review.
 
diff --git a/knowledge/docs/enforcement.md b/knowledge/docs/enforcement.md
index 497f391..92a35fb 100644
--- a/knowledge/docs/enforcement.md
+++ b/knowledge/docs/enforcement.md
@@ -57,3 +57,50 @@ not the merge button or mutable pull-request metadata.
 
 The doctor's D6 check flags a missing CODEOWNERS file or a Standing Knowledge path that
 the file does not cover.
+
+## A rule with no checker decays
+
+CODEOWNERS is one instance of a general finding, and the general finding is
+the reason to bother with any of layer 3.
+
+An Instance ran the experiment by accident. A four-dimension audit of its own
+repository — duplication, staleness, contradiction, graph structure — sorted
+every rule the organization held by one question: *is there a script that
+checks it?*
+
+| Rule | Mechanically checked? | Outcome |
+|---|---|---|
+| Links must resolve | yes | zero dangling, across 749 files |
+| Snapshots must be under 30 days old | yes | held — hard-stopped a stale purchase order |
+| No concurrent overwrite | yes | held — no lost write |
+| One fact, one home | no | the same rule found living in six places |
+| A cadence actually runs | no | three processes had never run once |
+| A control gets checked | no | every control's `last-checked` field empty |
+| A ruling propagates | no | a withdrawn fix still live in two governed files |
+
+**Every rule with a checker held. Every rule without one decayed — several
+within a day of being written.** The doctrine was not wrong and the operators
+were not careless; the rules with checkers and the rules without were written
+by the same people in the same week.
+
+Three consequences worth designing for:
+
+1. **Writing more doctrine does not fix a decay problem.** The decayed rules
+   were already written down, clearly, in Standing Knowledge. Restating them
+   adds a copy, which is itself the failure mode in row 4.
+2. **A field nothing writes is worse than no field.** An always-empty
+   `last-checked` reads as *not yet stale* to every consumer, so adding the
+   field without adding the writer made the gap harder to see, not easier.
+3. **The checker has to key on the thing that is true, not on a proxy for
+   it.** A governance route that ends "…and one recorded ruling" needs the
+   check to be *ruling artifact present*, not *commit message mentions a
+   ruling* — the route was followed three steps out of four several times, and
+   only the fourth step was the one that made the change findable later.
+
+So the practical test when adding any rule — asked by
+[AUTHORING.md's Standing Knowledge review](../AUTHORING.md#standing-knowledge-review):
+**name the script that will fail if it stops being true.** If there is none,
+either write one, or write the rule knowing it is guidance rather than an
+invariant — and say which it is, in the rule itself. A checker whose failures
+are routinely ignored has stopped being a checker; a red check nobody reads
+decays exactly like a rule nobody checks.