docs: record ontology self-amendment boundary

Author: LalaSkye

docs/governance/BUILD_RECEIPTS.md

@@ -33,6 +33,7 @@ This ledger records structural commits and the claim boundary attached to each s
 | `941a1521` | Governance class taxonomy | `docs/governance/GOVERNANCE_CLASSES.md` | Permitted governance trigger classes formally defined. |
 | `20223ea9` | Governance index taxonomy route | `docs/governance/README.md` | Governance class taxonomy exposed from the governance routing surface. |
 | `78e6a948` | Governance ontology amendment rule | `docs/governance/CHANGE_CONTROL.md` | Governance class ontology amendments must use the existing Mechanism change class. |
+| `98f07f80` | Ontology self-amendment boundary | `docs/governance/GOVERNANCE_CLASSES.md` | Governance class ontology cannot define a class for its own amendment. |
 
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@@ -58,6 +59,8 @@ Governance trigger classes are now formally defined and pinned.
 
 Governance class ontology amendments must use the existing Mechanism change class.
 
+Governance class ontology cannot define a class for its own amendment.
+
 ## Current unheld claim
 
 CI green proof is not yet evidenced through the connector.