@micr0 connecting protesters with suitable legal representation and advice: great idea ✅
doing it through an app: bad idea ❌
I have been involved in activist legal support in the past.
As has been pointed out, not bringing your phone to a protest is preferable. Cops can seize your phone, and just the fact you may have that app could make you a target of further investigation or hostility.
In the UK, "bust cards" have been handed out at protests for many years: they have the name and contacts of several law firms that specialize in protest and activism related law. These firms have been vetted and are trusted by activists, they have a relationship with social movements spanning decades. How will you ensure that the lawyers that sign up to this app are indeed trustworthy and have the necessary experience for these cases? Example: https://greenandblackcross.org/guides/bustcard/
Back in 2020, lots of lawyers were offering support to BLM protesters in the UK, but they didn't have the same experience or training that legal observers trained by activist collectives have.
Also, why do we need an app to do something that a piece of paper handed out anonymously or a phone number scribbled on your arm with a pen can do without giving away all the personal information that carrying a phone will? How do you know that these things aren't already happening in places like LA? I bet there are legal support activist collectives in most major US cities that have this background and experience. Perhaps donate your time or money to them instead of trying to develop another useless app.