Record SSH-signed keychain init ops

AGENTS.md

@@ -123,7 +123,10 @@ Roadmap items should be actionable and checkable:
   local KV write grants for non-local test callers. Signature validation and
   broader daemon-side module enforcement are still roadmap work.
 - The daemon persists local keychain init/admin-key ops and reduces them for
-  `keychain status`. SSH signature capture/verification is still roadmap work.
+  `keychain status`. `keychain init --signing-key <path>` signs recorded
+  keychain ops with `ssh-keygen -Y sign` under the
+  `geth.keychain.v1@geth.local` namespace and stores signatures locally.
+  Verification before accepting replicated keychain ops is still roadmap work.
 - Local CAS supports pin/unpin metadata, surfaced through `cas list`, and
   `cas cleanup` evicts unpinned blobs while retaining pinned blobs. The daemon
   can fetch CAS blobs from an imported signed peer card over Iroh when the peer