Lifetime bound not satisfied on trait impl whose signature is same as trait definition

I'm trying to make a trait for objects supporting std::thread::scope-like functionality. The trait definition itself compiles, but the implementation reports an error if I'm using Self::Scope. (playground link)

trait HasScoped {
    type Scope<'scope, 'env: 'scope>: Scope<'scope, 'env>;

    fn scope<'env, F>(&self, f: F)
    where
        F: for<'scope> FnOnce(&'scope Self::Scope<'scope, 'env>);
}

struct Thread {}

impl HasScoped for Thread {
    type Scope<'scope, 'env: 'scope> = std::thread::Scope<'scope, 'env>;

    fn scope<'env, F>(&self, f: F)
    where
        // lifetime bound not satisfied:
        F: for<'scope> FnOnce(&'scope Self::Scope<'scope, 'env>),
        // But this compiles:
        // F: for<'scope> FnOnce(&'scope std::thread::Scope<'scope, 'env>),
    {
        std::thread::scope(f);
    }
}

trait Scope<'scope, 'env: 'scope> {
    fn spawn<T: FnOnce() + Send + 'scope>(&'scope self, obj: T);
}

impl<'scope, 'env: 'scope> Scope<'scope, 'env> for std::thread::Scope<'scope, 'env> {
    fn spawn<T: FnOnce() + Send + 'scope>(&'scope self, obj: T) {
        self.spawn(obj);
    }
}

I expected to see this happen: Compiles without errors. The HasScoped::scope impl signature is an exact copied of its definition in the trait.

Instead, this happened:

error[E0478]: lifetime bound not satisfied
  --> src/lib.rs:17:12
   |
17 |         F: for<'scope> FnOnce(&'scope Self::Scope<'scope, 'env>),
   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: lifetime parameter instantiated with the lifetime `'env` as defined here
  --> src/lib.rs:14:14
   |
14 |     fn scope<'env, F>(&self, f: F)
   |              ^^^^

error[E0478]: lifetime bound not satisfied
  --> src/lib.rs:17:24
   |
17 |         F: for<'scope> FnOnce(&'scope Self::Scope<'scope, 'env>),
   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: lifetime parameter instantiated with the lifetime `'env` as defined here
  --> src/lib.rs:14:14
   |
14 |     fn scope<'env, F>(&self, f: F)
   |              ^^^^

For more information about this error, try `rustc --explain E0478`.

If I write std::thread::Scope directly instead of Self::Scope in the impl block, then it compiles. But as defined, Self::Scope<..> should be the same type as std::thread::Scope<..> thus should result in the same behavior.

Meta

Reproduced on stable rustc (1.93.1) and nightly (1.95.0-nightly 2026-02-23 b3869b94cd1ed4bfa2eb) on playground.

Start with the linked Rust Playground reproducer and compare the trait definition and impl using Self::Scope with the version using std:🧵:Scope. Investigate the E0478 diagnostics on stable 1.93.1 and nightly 1.95.0, then confirm whether the impl accepts the same signature and lifetime bounds without errors.