The httpmock generator currently stringifies all query/header/path params via value.to_string() (see progenitor-impl/src/httpmock.rs). This implicitly requires Display and only supports single-value params.

For array query params (e.g., Vec), Display isn’t implemented and the generated mocks won’t compile.

It also doesn’t match the client’s actual query encoding (QueryParam uses serde and supports arrays by repeating the key). Should switch httpmock query matching to use the same serialization logic as the client.