* refactor: on-demand getSharedSecret()

src/helpers/ContactInfo.h

@@ -12,8 +12,18 @@ struct ContactInfo {
   mutable bool shared_secret_valid; // flag to indicate if shared_secret has been calculated
   uint8_t out_path[MAX_PATH_SIZE];
   uint32_t last_advert_timestamp;   // by THEIR clock
-  mutable uint8_t shared_secret[PUB_KEY_SIZE];
   uint32_t lastmod;  // by OUR clock
   int32_t gps_lat, gps_lon;    // 6 dec places
   uint32_t sync_since;
+
+  const uint8_t* getSharedSecret(const mesh::LocalIdentity& self_id) const {
+    if (!shared_secret_valid) {
+      self_id.calcSharedSecret(shared_secret, id.pub_key);
+      shared_secret_valid = true;
+    }
+    return shared_secret;
+  }
+
+private:
+  mutable uint8_t shared_secret[PUB_KEY_SIZE];
 };