This may be a known limitation, or even designed in, but we've stumbled across an interesting case of class naming as an issue:

// We might be using a string to run logic around loops/interpolation
$some_class = "\\Namespace\\ClassName";
$container->add($some_class);

Elsewhere

$container->get(ClassName::class)

This later access will not find the existing entry due to the leading slashes.

I wonder if there's a case for stripping leading slashes during name resolution - I can't see a situation where somebody would want "$key" and "\\$key" to resolve differently, and it avoids this being a hard-to-spot bug in a larger container setup.

Happy to PR for the feature if acceptable.