okf: add optional erasure conformance profile (SPEC 9.1)

okf/SPEC.md

@@ -361,6 +361,26 @@ This permissive consumption model is intentional: OKF is meant to
 remain useful as bundles grow, get refactored, and are partially
 generated by agents.
 
+### 9.1 Erasure profile (optional)
+
+Deleting a concept file removes its content, but a plain deletion can still
+*disclose* that the concept once existed: dangling links from other concepts
+continue to name it, `index.md` and `log.md` may still reference it, and in a
+git-distributed bundle the content remains recoverable from history. Bundles
+that must not leak erased knowledge MAY declare conformance with the **erasure
+profile**, which requires that, when a concept is erased:
+
+1. Inbound links to it from other concepts in the same revision are removed or
+   redacted, so no dangling reference names the erased concept.
+2. Its concept ID no longer appears in any `index.md` or `log.md`.
+3. Where the distribution history itself must not disclose the concept, the
+   erasure is realized by rewriting history (for example, a fresh export)
+   rather than an additive deletion commit.
+
+The erasure profile is opt-in. Consumers MUST NOT assume a bundle follows it
+unless the bundle states so, and MUST NOT treat a non-conforming bundle as
+malformed — ordinary bundles remain valid under the rules above.
+
 ---
 
 ## 10. Relationship to other formats