I've been noticing lately (using r38647) something I think is a change: when a fleet (player or AI) fights at a planet in a system and retreats, it retreats to another system even if there are other friendly planets in the system. In the player's case the fleet can be ordered back, but there's that built-in delay so it takes 2 turns to return to the system it's retreating "from". (** It appears this is incorrect - the map displays "2 turns", but at least in my current late-game, it actually takes just 1.)

I thought (but my memory may be faulty) that SiS used to handle retreats like MOO2: if a fleet gets its butt kicked in a system & retreats, but other friendly planets remain in the same system, it doesn't actually leave the system. This makes sense to me, both gameplay-wise and in terms of rationale - the attackers clearly are not attacking every planet at once, we know that's not happening because the game doesn't allow that.

I see this in the r38550 patch notes, which probably explains things:
"Retreating ships may no longer "retreat" towards the system they're leaving."

But: I would suggest this behaviour is cracked, and encourages exploitative behaviour (by the AI or the player). Previously (if my memory is correct), or in MOO2, the player may essentially ignore an attack on a minor planet to preserve their fleet for a fight at a major planet with planetary defenses and orbitals - doing so by immediately retreating from the attacker-forced battle at some minor outpost. Often good strategy, sacrificing some doomed little rock.

Now, however, a retreat means the fleet can't be back in the system next turn, which means a very simple exploit is to always attack the weakest link in a system. A weak defender that might have survived at their fortress world no longer has a way to confine their defense to that one world, and instead must have their fleet be wiped out in a disadvantageous situation, or preserve it and have no ships present for the next turn's battle at the fortress.

As a lousy player who often finds himself attacked by superior-but-not-hugely-superior forces, this change is costing me a lot of systems. On the other hand, it's also making taking on Raider worlds much easier: I enter their system, the Raiders attack my fleet away from their world, retreat to some other system, and I wipe out the world's defenses without the raider ships interfering. I shouldn't be able to do that.

I don't know what this fix was attempting to correct, but to me it looks like a bad exchange. One should always be able to retreat in-system if one has a base left - only in retreating from the last base defense battle should one get chased out of the system entirely.

At the level of the core game rules, a player is not obligated to commit their ships to a defensive battle unless they have 0 or 1 controlled planets in the system. Thus, technically, if you're attacked in a system where you have 2 worlds (one well defended one, and one outpost), you can decline to commit your fleet when the outpost is attacked, and save those ships for the defense of the key world. The AI has this right as well.

That said, what's permitted in the core game rules, and what's easily discovered in the UIs are often very different things.

As a player, to make use of the "decline to commit" rule, what you need to do is left-click on the ships you want to hold back from combat in the "attacked at" pane. They'll grey out, won't join the combat, and will stay in system to defend your other worlds.

Given that this "decline to participate" mechanic exists, I think the rules are ok as they are. However, the fact that players can't easily discover the mechanic is a game design problem that Arioch and I should perhaps talk through.

Oh my gosh. Thank you so much.

Yes, it's totally 100% fine as it is, in terms of mechanics. I had no idea. And I never thought to try clicking on ships to change commitments, which wasn't smart of me.

While thinking of interface improvements, umm... do please consider some hover-text or other way to show hotkeys too, please! (Is there one for "end turn" in combat?") But that's just icing. The game is already some delicious cake, thanks.

Some kind of "Ignore" or "Decline" button would probably be beneficial.