Thing like #![feature(duration_constructors)] must be placed before any doc comment, but /// \``cargo` doc comment (apparently) must be placed before crate-level attributes (or anything else, really).
So this is a deadlock situation.
#!/usr/bin/env rust-script
/// ```cargo
/// [dependencies]
/// chrono = "0.4.38"
/// ```
#![feature(duration_constructors)]
#!/usr/bin/env rust-script
#![feature(duration_constructors)]
/// ```cargo
/// [dependencies]
/// chrono = "0.4.38"
/// ```
This means that such attributes type (crate-level) must be ignored/skipped by rust-script or something (I don't know the implementation).