docs: capture protocol and implementation gaps

packages/protocol/simplesync.proto

@@ -0,0 +1,28 @@
+syntax = "proto3";
+
+package mdhub.protocol.v1;
+
+option go_package = "github.com/tim/md-hub-secure/packages/protocol/gen/go/mdhub/protocol/v1;protocolv1";
+
+message SyncRequest {
+  string client_id = 1;
+  string root_hash = 2;
+  map<string, string> files = 3;
+}
+
+message SyncResponse {
+  string server_root_hash = 1;
+  repeated string missing_from_client = 2;
+  repeated string missing_from_server = 3;
+  repeated string conflicts = 4;
+}
+
+message ContentRequest {
+  string hash = 1;
+}
+
+message ContentResponse {
+  string hash = 1;
+  bytes content = 2;
+}
+