Honestly, that is the whole problem with 100% Hard Scifi. Space Warfare would be beyond exceptionally hard. I won't say impossible. But I seriously doubt it'd be between "battle lines" of fleets. Most likely it would be a case of long-ranged sniping of relatively static installations. Asteroid bases. Colonies. Pubs.
Hell it is one area Mass Effect got hell as right too. If both sides are fighting "responsibly" then neither side would fire a single shot until it had a guaranteed hit lined up. (As Kinetic projectiles would just keep going.) Missiles would be next to useless as time goes on any computing makes it basically impossible for point defence to miss or fail.
Realistic Hard-Scifi Space Battles are. Well to put it bluntly, far from being "fun" it'd probably be 99 parts boredom 1 part action.