I think I have played my first few games incorrectly. Do characters must commit to a quest each round? I think my first hasty read-through of the rules made me think they were committed until the quest was done...

character/heros commit to a quest and remained exhausted (un useable) until the end of the round, then they refresh at the begining of the next round

And then the next round I will have to commit/exhaust them again to make progress, right?

yes, basically unless you get a card like caught in a web which traps a character so they cant refresh without paying, everything switchs back to a 'new' stance each round, apart from enemies engaged of course, but thats a different matter

My confusion is not over the exhaust/ready mechanic but rather the "commit to a quest" mechanic." To make progress on a quest, one commits characters each round during the quest phase, correct? I originally thought "once committed, always committed to the quest," so I did not exhaust them every round, but rather just one round.

You have to recommit characters every round.

Just to be sure we're entirely on the same page it would go like this:

Round begins

You go through Phase 1

You go through Phase 2

Phase 3: You choose characters and commit them to a quest. You lay out one encounter card. You resolve the quest.

When Phase 3 ends, your characters are no longer committed to any quests.

When it says they remain committed to the quest, it means throughout Phase 3. This comes into play with characters like Aragorn, who can ready himself immediately after committing to a quest. Even though he's now ready, he's still committed to the quest throughout Phase 3.

Hope that helps

ah yes i see now, the above is correct, committing to questing or other actions such as defending, attacking, is an on going process, as this takes into account for killed allies/heros and also new cards played from your hand