That doesn't cover tracking pull requests, discussing them, closing them, making suggestions on them...
Those exist (badly and not integrated) as part of additional tools such as email, or as tasks done manually, or as part of forge software.
I don't think there's much point in splitting this hair further. I stand by the original statement that I'd love to see federated pull requests between forges, with all the capabilities people expect of a modern forge.
What is a forge? What is a modern forge? What is a pull request?
There is code or repository, there is a diff or patch. Everything else your labeling as pull request is unknown, not part of original design, debatable.
I think people (especially those who joined the internet after the .com bubble) underestimate the level of decentralization and federation coming with the old-school (pre web-centric mainframe-like client mentality) protocols such as email and Usenet and maybe even IRC.
Give me “email” PR process anytime. Can review on a flight. Offline. Distraction free. On my federated email server and have it work with your federated email server.
And the clients were pretty decent, at running locally. And it still works great for established projects like Linux Kernel etc.
It’s just pain to set up for a new project, compared to pushing to some forge. But not impossible. Return the intentionality of email. With powerful clients doing threading, sorting, syncing etc, locally.