feat(fof-layer2): wire types — WrapSlot, FoFCommentGating, CommentPermission::FriendsOfFriends

Adds the on-wire shapes for FoF Mode 2 comment-gating per
docs/fof-spec/layer-2-mode2-fof-comments.md:

- WrapSlot: per-V_x slot with 2B prefilter_tag + 48B read_ciphertext
  + 48B sign_ciphertext (sealed CEK + sealed priv_x_seed). 98 bytes
  total per slot. Receiver trial-decrypts via prefilter match.

- FoFCommentGating: author-published gating block embedded in
  Post.fof_gating. Carries slot_binder_nonce (32B random; replaces
  spec's circular "post_id in HKDF info"), pub_post_set (1:1 with
  wrap_slots, includes dummy pubkeys), wrap_slots, and revocation_list
  (initially empty; revocation diffs accumulate on the BlobHeader copy).

- RevocationEntry: author-signed entry triggering retroactive comment
  delete + pub_post_set removal on every file-holder that receives it.

- CommentPermission gains FriendsOfFriends variant. Existing match arm
  in connection.rs handle-incoming-diff path is extended with a
  "drop pending CDN four-check verification" stub (full verify in a
  later slice).

- InlineComment extended with three optional fields:
    pub_x_index: index into parent post's pub_post_set
    group_sig: 64B ed25519 sig under priv_x
    encrypted_payload: ChaCha20-Poly1305 ciphertext under CEK_comments
  All #[serde(default)] for back-compat. Old comments deserialize
  cleanly with None.

- Post gains optional fof_gating field for the author-signed snapshot
  at publish time. PostId = BLAKE3(Post) covers it, so any tampering
  is detectable. Mutations (revocation, access-grant) arrive later as
  diffs against the local BlobHeader copy.

All 21 existing Post construction sites + 4 existing InlineComment
sites updated via perl -0pe sweeps to pass None for the new fields.
Full test suite: 134/134 pass (4 new slot crypto + 130 existing).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/core/src/storage.rs

@@ -893,6 +893,7 @@ impl Storage {
                 content: row.get(1)?,
                 attachments,
                 timestamp_ms: row.get::<_, i64>(3)? as u64,
+            fof_gating: None,
             }))
         } else {
             Ok(None)
@@ -919,6 +920,7 @@ impl Storage {
                     content: row.get(1)?,
                     attachments,
                     timestamp_ms: row.get::<_, i64>(3)? as u64,
+                fof_gating: None,
                 },
                 visibility,
             )))
@@ -1012,6 +1014,7 @@ impl Storage {
                     content,
                     attachments,
                     timestamp_ms: timestamp_ms as u64,
+                fof_gating: None,
                 },
                 visibility,
             ));
@@ -1050,6 +1053,7 @@ impl Storage {
                     content,
                     attachments,
                     timestamp_ms: timestamp_ms as u64,
+                fof_gating: None,
                 },
                 visibility,
             ));
@@ -1212,6 +1216,7 @@ impl Storage {
                     content,
                     attachments,
                     timestamp_ms: timestamp_ms as u64,
+                fof_gating: None,
                 },
                 visibility,
             ));
@@ -1247,6 +1252,7 @@ impl Storage {
                     content,
                     attachments,
                     timestamp_ms: timestamp_ms as u64,
+                fof_gating: None,
                 },
                 visibility,
             ));
@@ -2926,6 +2932,7 @@ impl Storage {
                     content: row.get(2)?,
                     attachments,
                     timestamp_ms: row.get::<_, i64>(4)? as u64,
+                fof_gating: None,
                 },
                 visibility,
             ));
@@ -5302,6 +5309,9 @@ impl Storage {
                 signature: sig,
                 deleted_at: None,
                 ref_post_id,
+            pub_x_index: None,
+            group_sig: None,
+            encrypted_payload: None,
             });
         }
         Ok(result)
@@ -5341,6 +5351,9 @@ impl Storage {
                 signature: sig,
                 deleted_at: del.map(|v| v as u64),
                 ref_post_id,
+            pub_x_index: None,
+            group_sig: None,
+            encrypted_payload: None,
             });
         }
         Ok(result)
@@ -6100,6 +6113,7 @@ mod tests {
                 content: format!("post at {}", ts),
                 attachments: vec![],
                 timestamp_ms: ts,
+            fof_gating: None,
             };
             let id = blake3::hash(&serde_json::to_vec(&post).unwrap());
             s.store_post(id.as_bytes(), &post).unwrap();
@@ -6797,6 +6811,9 @@ mod tests {
             signature: vec![0u8; 64],
             deleted_at: None,
             ref_post_id: None,
+        pub_x_index: None,
+        group_sig: None,
+        encrypted_payload: None,
         }).unwrap();
 
         s.store_comment(&InlineComment {
@@ -6807,6 +6824,9 @@ mod tests {
             signature: vec![1u8; 64],
             deleted_at: None,
             ref_post_id: None,
+        pub_x_index: None,
+        group_sig: None,
+        encrypted_payload: None,
         }).unwrap();
 
         let comments = s.get_comments(&post_id).unwrap();
@@ -6832,6 +6852,9 @@ mod tests {
             signature: vec![9u8; 64],
             deleted_at: None,
             ref_post_id: Some(ref_post),
+        pub_x_index: None,
+        group_sig: None,
+        encrypted_payload: None,
         }).unwrap();
 
         let live = s.get_comments(&post_id).unwrap();