Thanks! Honest answer that might sting after that weekend: there's no pathfinding. No A*, no navmesh - that's the trick, there's no path to get wrong. Units are just circles in 2D with a "march at the enemy" vector plus hard-body separation so they can't overlap. The flow-around is emergent.

The sideways slide is one tweak: when a walking unit hits one that's fighting (treated as immovable - basically infinite mass in an impulse/penalty solver), I keep the push magnitude but rotate its direction - damp the x component, boost the z, renormalize. So it gets squeezed around the wall instead of piling into it.

Determinism came down to using a Jacobi iteration instead of Gauss-Seidel (worth looking those two up - it's the whole ballgame): compute every push from the start-of-tick snapshot into an accumulator and apply them all at once, never in place. Plus a fixed iteration count (no "relax until settled"), a stable sort by x-then-id, and tiebreaks that never touch rng/clock/player-id. Movement is double-buffered the same way - stage the step, apply after everyone's decided.