And the reason it works in anyhow is ... They have those conversions: https://docs.rs/anyhow/latest/anyhow/struct.Error.html#impl-From%3CError%3E-for-Box%3Cdyn%

And the reason it works in anyhow is ... They have those conversions: https://docs.rs/anyhow/latest/anyhow/struct.Error.html#impl-From%3CError%3E-for-Box%3Cdyn%20StdError%20+%20%27static%3E https://docs.rs/anyhow/latest/anyhow/struct.Error.html#impl-...