Exceptions

Both exceptions implement the PSR-11 interfaces, so code that depends only on psr/container can catch them:

Exception	PSR-11 interface	Meaning
Solo\Container\Exceptions\NotFoundException	NotFoundExceptionInterface	the id passed to get() is unknown
Solo\Container\Exceptions\ContainerException	ContainerExceptionInterface	the id is known, but its entry cannot be built

Both extend \Exception, and neither extends the other. PSR-11's NotFoundExceptionInterface extends ContainerExceptionInterface, so catch the interface to handle both:

use Psr\Container\ContainerExceptionInterface;

try {
    $service = $container->get($id);
} catch (ContainerExceptionInterface $e) {
    // NotFoundException or ContainerException
}

An exception thrown by a factory reaches the caller of get() as it is, with one exception: a PSR-11 NotFoundExceptionInterface — the factory asked a container for an id it does not have — becomes a ContainerException, as below.

NotFoundException

Service 'mailer' not found in container.

Thrown by get() when the requested id has no factory and no binding and names no existing class — including an interface that is neither bound nor registered, and an id marked lazy() that resolves to nothing.

A missing dependency is not a missing entry: while an entry is built, a NotFoundException becomes a ContainerException that names the chain and keeps it as its previous exception, as PSR-11 requires.

ContainerException

Thrown when an entry is known but cannot be built:

Message	Cause
Service 'X' is Y, not an instance of X.	a factory or binding under a class or interface name that yields something else
Cannot resolve A -> B: Service 'C' not found in container.	a dependency the container does not know, needed while building A and then B
Class 'X' is not instantiable.	an abstract class, an enum, a class with a non-public constructor
Cannot resolve parameter '$x' in class 'Y'.	a parameter with no class type, no default and no #[Inject]
Circular dependency detected: A -> B -> A	a cycle in auto-wiring, bindings or factories
Cannot create a lazy proxy for 'X': …	a lazy id or #[Lazy] parameter that does not resolve to a class PHP can proxy
Cannot initialize the lazy proxy for 'X': it resolved to Y, not an instance of exactly C.	on first use, a lazy id or #[Lazy] parameter whose entry is not an instance of exactly the proxied class C
Service 'id' injected into '$x' in class 'Y' is Z, not T.	an #[Inject] value, or the proxy of a #[Lazy] parameter, that does not match the parameter type
Invalid #[Inject] on '$x' in class 'Y': …	an #[Inject] without an id, or repeated