well the thing is flat out a citizen cannot, by definition, claim Qualified immunity, because the doctrine from it's inception has been restricted to government actors (i.e. the police)- thus it follows that citizens will never be able to have such an easy defense. The term "Detainment" actually takes root out of federal case law- See e.g. Terry v. Ohio, 392 U.S. 1 (1968). (which is binding precedent in MO, as it is in all states.) Notably, Terry and its progeny doesn't authorize a law enforcement officer to transport a person away from the place at which an officer finds an individual. Therefore, in essence the transport will generally tend to mark the difference between detention and arrest in that context. However, notably, the court has never extended Terry doctrine to the context of citizen's arrest or the like. Therefore, in essence if a citizen were to detain under the circumstances described in Terry, the judiciary is likely to see it as an "arrest".Arrest may or may not be defined in any state's statutes. In MO, arrest is defined. Restraint in MO via the use of handcuffs, by a cop, is a arrest. There is no detainment in MO, under the law, which means that the cop safety canard does not exist in MO, under the law. Then there is what the courts will decide (interpret) based on their precedent.
I have found no evidence to indicate if a citizen "detained" has pursued a legal remedy for being "falsely arrested: where the cop did/could not inform the defendant by what authority he acts.
QI extends to cops making mistakes thus the use of the term immunity...Heien strengthened QI...abolish QI!!!
QI is not needed if the cop is acting within the confines of any particular state statute or municipal code...nor would (should?) a citizen be prosecuted.