If you want a messaging app to work well, it should send and receive messages when the phone has network connectivity and power. Power is a prerequisite for running in the foreground, but network connectivity is not. Some people may in fact want messaging apps to only work while in the foreground and network available, but I suspect that's less desired.
If you're trying to run standard irc and appear online as much as possible, that's not going to work in iOS without a bouncer to stay online for you and send push messages to send notifications and allow the app to run for a bit to download the messages.
It's probably not a bad idea on Android too, it's technically possible to run as a background service and stay connected, but there's a lot of uncertainty, because other services can crowd you out, and you're at the whim of Google and oems with power management these days.
And also, it's the 21st century and we don't need chat protocols to be client-side-liveness chatty to "stay on" when the entire cellular network is architected to find devices and route messages to them.
IRC isn't a well-designed protocol for this use case, and a "land-side" bouncer that bridges the chatty protocol to a lazier protocol ought to be more energy-efficient overall.
That's fine. you are "free" to hack your own version of Android that modifies the APIs to disregard power-management best practices.
... and maybe your own hardware to run them on. But I wouldn't expect any major player competing against other companies to do the work for you when the outcome is supporting some chat protocols that most people don't use.
(Otherwise, if you're expecting vendors to do it for you, you get to expect the lecture that comes with that expectation, in the form of APIs designed to minimize the ease of doing the wrong-for-the-average-utility-of-the-platform thing. Your cell radio could probably be adjusted to operate as a spark-gap transmitter also, but I don't expect them to provide an easy API for that either ;) ).
If you're trying to run standard irc and appear online as much as possible, that's not going to work in iOS without a bouncer to stay online for you and send push messages to send notifications and allow the app to run for a bit to download the messages.
It's probably not a bad idea on Android too, it's technically possible to run as a background service and stay connected, but there's a lot of uncertainty, because other services can crowd you out, and you're at the whim of Google and oems with power management these days.