Trust is a word, and each individual may trust that each other individual agrees with their individual interpretation of the word trust. Is that trustworthy?

"Constitutions, statutes, rules, axioms, and all verbal formulas are subject to various and conflicting interpretations, all growing out of the inherent and indestructible Individuality of different minds. A compact between parties who do not understand it alike is null and void, because they have not consented to the same thing, even if they have signed it! What is to be done with this fact? We can do nothing with it but accept it as an irrefutable truth, and provide means of dispensing with whatever conflicts with it."
True Civilization.
Warren, Josiah
(1863) Boston, Mass.

"Is trust anything other than predictability?"

That appears to be an agreeable definition of trust: predictable human behavior. I would add that trust is - to me - predictable human behavior applied to risk assessment.

"Does it necessarily have to be a positive emotion experience to be functional?"

To me, no. I trust that a government based upon aggressive use of deception, threat of violence, and routine demonstrations of aggressive violence is - without emotion clouding judgment - the same as organized crime based upon the same methods (means) to reach the same goals: subsidized slavery.

Trust in government based upon voluntary defense, on the other hand, is a prediction concerning the assessment of risk when investing in government. If things go bad, I trust that I can pull the plug by ending my voluntary contributions.