Optional replyId on send (API + MCP) — protocol-level threaded replies (#31)

src/mesh/codec.ts

@@ -126,6 +126,7 @@ export async function buildTextToRadio(
   to: number,
   text: string,
   channelIndex: number,
+  replyId?: number,
 ): Promise<{ bytes: Uint8Array; id: number }> {
   const P = await loadProto();
   const id = randomPacketId();
@@ -140,6 +141,8 @@ export async function buildTextToRadio(
         portnum: P.Portnums.PortNum.TEXT_MESSAGE_APP,
         payload: new TextEncoder().encode(text),
         wantResponse: true,
+        // camelCase on purpose — the JS protobufs package silently drops snake_case reply_id; 0 = not a reply (proto3 default, omitted from wire)
+        replyId: replyId ?? 0,
       },
     },
   });