proto: gateway, the four messages between brokerd and gatewayd

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/brokerd/src/broker.rs

@@ -87,7 +87,7 @@ impl Broker {
     }
 }
 
-/// The snake_case wire name of a message: all fourteen kinds, none with a leading underscore.
+/// The snake_case wire name of a message: all eighteen kinds, none with a leading underscore.
 pub fn kind(msg: &Message) -> &'static str {
     match msg {
         Message::ToolRequest(_) => "tool_request",
@@ -104,6 +104,10 @@ pub fn kind(msg: &Message) -> &'static str {
         Message::Ok(_) => "ok",
         Message::CheckGrants(_) => "check_grants",
         Message::GrantsReport(_) => "grants_report",
+        Message::ApprovalRequest(_) => "approval_request",
+        Message::ApprovalPosted(_) => "approval_posted",
+        Message::ApprovalReply(_) => "approval_reply",
+        Message::ApprovalOutcome(_) => "approval_outcome",
     }
 }