Diagnostic does not fire on marker trait that requires static

Code

#[diagnostic::on_unimplemented(
    message = "Arguments to embassy tasks must be 'static",
    label = "Not 'static",
    note = "See https://embassy.dev/... for more details on sharing",
)]
trait SecretStatic {
}

// // Option A
impl<T: 'static> SecretStatic for T {
    
}
// //

// Option B
// impl SecretStatic for i8
// {
// }

// impl SecretStatic for u16
// {
// }

// impl SecretStatic for u32
// {
// }
//

fn expanded_func<T, U, V>(t: T, u: U, v: V)
where
    T: SecretStatic,
    U: SecretStatic,
    V: SecretStatic,
{
    todo!()
}

struct Example {
    x: u32,
}

fn main() {
    expanded_func(1i8, 2u16, 3u32);
    let x = Example { x: 123 };
    expanded_func::<&Example, u16, u32>(&x, 2u16, 3u32);
}

Current output

error[E0597]: `x` does not live long enough
  --> src/main.rs:45:41
   |
44 |     let x = Example { x: 123 };
   |         - binding `x` declared here
45 |     expanded_func::<&Example, u16, u32>(&x, 2u16, 3u32);
   |     ------------------------------------^^-------------
   |     |                                   |
   |     |                                   borrowed value does not live long enough
   |     argument requires that `x` is borrowed for `'static`
46 | }
   | - `x` dropped here while still borrowed

For more information about this error, try `rustc --explain E0597`.

Desired output

error[E0277]: Arguments to embassy tasks must be 'static
  --> src/main.rs:45:21
   |
45 |     expanded_func::<&Example, u16, u32>(&x, 2u16, 3u32);
   |                     ^^^^^^^^ Not 'static
   |
   = help: the trait `SecretStatic` is not implemented for `&Example`
   = note: See https://embassy.dev/... for more details on sharing
   = help: the following other types implement trait `SecretStatic`:
             i8
             u16
             u32
note: required by a bound in `expanded_func`
  --> src/main.rs:31:8
   |
29 | fn expanded_func<T, U, V>(t: T, u: U, v: V)
   |    ------------- required by a bound in this function
30 | where
31 |     T: SecretStatic,
   |        ^^^^^^^^^^^^ required by this bound in `expanded_func`

Rationale and extra context

We want to use a marker trait in macro expanded code for the embassy executor so that all arguments to tasks are 'static. This is a limitation of the executor, and is a common stumbling block for users.

We wanted to use diagnostics for this to reduce the amount of work required in a proc macro to get good spans and errors, but noticed that diagnostics did not fire at all. They DO fire when we manually add impls for the type instead of using a blanket impl (this is not practical to support for arbitrary user types

Other cases

No response

Rust Version

Tested with 1.81.0 stable and 1.82.0-beta.6, same output

Anything else?

No response

Start by reproducing the issue with the provided marker-trait example on the reported Rust versions, then trace how on_unimplemented diagnostics are handled for blanket implementations requiring 'static. Done means the reproduction emits the requested E0277 message, label, note, and trait-bound context instead of E0597.