I created pre-rel-v0.13.0-rc6 to make easier testing the changes.

Included test covers case of RpcMessage with Item of unit type (()) - it was the unsupported case I needed to handle.
Every other type of response should work too, but I did not manage to test them.
Among them are:

• enum

  yagna/core/model/src/activity.rs

  Line 51 in cb75608

  type Item = CreateResponseCompat;

• Option (special enum?)

  yagna/core/model/src/driver.rs

  Line 123 in e42ede5

  type Item = Option<GasDetails>;

• vec u8

  yagna/core/model/src/activity.rs

  Line 206 in cb75608

  type Item = Vec<u8>;

• String

  yagna/core/model/src/activity.rs

  Line 225 in cb75608

  type Item = String;

• vec struct

  yagna/core/model/src/activity.rs

  Line 244 in cb75608

  type Item = Vec<ExeScriptCommandResult>;

• tuple

  yagna/core/model/src/appkey.rs

  Line 120 in cb75608

  type Item = (Vec<AppKey>, u32);

• number

  yagna/core/model/src/appkey.rs

  Line 138 in cb75608

  type Item = u64;

• struct (but empty - I wonder if it will be {} or null)

  yagna/core/model/src/driver.rs

  Line 269 in cb75608

  type Item = Ack;

• bool

  yagna/core/model/src/driver.rs

  Line 356 in cb75608

  type Item = bool;

• map

  yagna/core/model/src/payment.rs

  Line 412 in cb75608

  type Item = HashMap<String, DriverDetails>;

It was implemented outside of scope of any task, and tests cover cases we are interested in.
Maybe we could merge it if SDK team app will start to work, and for additional tests we could create a task?

SDK confirmed it solves the problem they faced.