After I wrote I had to run some errands. The local NPR station had many local reports about last night's riots. In an interview with the police chief, he said that the feds were coordinating with the local police until a few weeks ago when these unidentified federal people came in and then the feds went completely silent. He said this has never happened before.
From some reporters who were there last night and had reported on protests before, normal procedure in these sorts of situations is that when people are gathering like this law enforcement first issues a warning to the protesters telling them to disperse or the police will use force to break up the protest. Following an incident like this there will be a press conference where the police involved will explain what happened. These police gave no warnings and have had no public statements at all.
As far as what happened last night (according to an eye witness reporter), a group of mothers with some fathers formed a human wall in front of the doors of the court house before midnight. The federal people were all inside the courthouse. There was a lot of chanting and such, but fairly peaceful. About 12:30 the feds burst out of the court house firing tear gas, pepper balls, and rubber bullets indiscriminately with no warning. That's when the riot kicked off.
Rioting is not an appropriate response, but the people who are acting as law enforcement (we know there are some US marshals in the group, but we don't know for sure what the law enforcement credentials of all these people are), have not followed normal procedures in this situation.
Oregon Law requires law enforcement to notify protesters to disperse
ORS 131.675 - Dispersal of unlawful or riotous assemblages - 2020 Oregon Revised Statutes
It states law enforcement must give notice to disperse before using force to disperse a gathering.
Now whether this applies to federal law enforcement or not, this falls back on a SCOTUS opinion from 1890 called the Neagle decision. It's been cited many times since in cases where states try to bring federal employees to task for violating state laws. The most current decision was by the 9th Circuit Court of Appeals in Idaho v Horiuchi who was the FBI sniper who shot Randy Weaver's wife at Ruby Ridge. They ruled that the FBI agent was acting unreasonably and Horiuchi could be prosecuted under Idaho law.
My SO has pointed out in making a determination of whether the feds crossed the line is an objectively reasonable test and she believes the feds fail it. If the State of Oregon can win on the objective reasonableness argument in court, then qualified immunity goes away for the feds. The current AG of Oregon is one of the most experienced state AGs in the country. She's been a judge on the Oregon state court of Appeals and a federal prosecutor.