Strategic map combat questions

[Noyyau]

I'm (finally) fighting a proper war with fleet engagements and planetary invasions and so on.
When two fleets meet in a star system, I get to choose between auto-resolving or manually commanding the battle or autoretreating. The option to fight it out can be either "Attack" or "Defend", which determines, as far as I've seen so far, the side of the screen you start on and who goes first. (Attacker on the left, defender on the right with planets and space stations as applicable, defender goes first).
What I do not fully understand is the logic that decides who "attacks" and who "defends".
Examples:
-when exploring an unknown star system and finding there hostiles (pirates or star harpies), the message is "Attacked at [STAR]" and the fighting option is "defend". I suppose this is to give the scouts a chance to escape, as by being "defender" they get to move first.
-when attacking a planet with no defending fleet in the system but with planetary defenses, the option is "Attack" and the fight is my (attacking) fleet vs the (defending) planet (and space stations if present). This is straightforward, no questions here.
-when an enemy fleet arrives at one of my planets though, is when things get weird: I have a planet with planetary defenses and a star base (the armed and armored space station). I also have moved my own fleet so that it arrives at the attacked system the same turn that the enemy does. The message I get is "[ENEMY] encounter at [SYSTEM]", with the icons colored yellow rather than red (same as when I end up in a system owned by someone else with whom I'm not at war, or when neutral ships arrive at one of my systems), and the combat option is "Attack", when I would have expected "Defend" (this being my star system). The combat, as the option name says, has my fleet as the "attacker" and the enemy as the "defender". My planet and star base are nowhere to be seen.
I was expecting to have a battle with all of my assets at the system: fleet, planet (planetary defenses) and star base all together. What am I missing or doing wrong?
Or are the star bases and planetary defenses there only as a last defense when no fleet is available? Feels a bit of a waste to spend all that metal (star base) and upkeep (plan. def.) on static defenses that, against mobile attackers, are fundamentally at a disadvantage.

On a side note, it's a nice touch that when civilian transports arrive at a system with hostile warships, the auto-resolve result is that the civilian transports surrender. Now that I know about it, sending even just a small light cruiser to capture long-distance enemy civilian tranports at their arrival is a nice way to get bonus alien populations (and free transports too!).
And with the Ashdar Haduir (Imperial) relic gate that's ridicoulously easy.

[AMX]

-when an enemy fleet arrives at one of my planets though, is when things get weird: I have a planet with planetary defenses and a star base (the armed and armored space station). I also have moved my own fleet so that it arrives at the attacked system the same turn that the enemy does. The message I get is "[ENEMY] encounter at [SYSTEM]", with the icons colored yellow rather than red (same as when I end up in a system owned by someone else with whom I'm not at war, or when neutral ships arrive at one of my systems), and the combat option is "Attack", when I would have expected "Defend" (this being my star system). The combat, as the option name says, has my fleet as the "attacker" and the enemy as the "defender". My planet and star base are nowhere to be seen.
I was expecting to have a battle with all of my assets at the system: fleet, planet (planetary defenses) and star base all together. What am I missing or doing wrong?
Or are the star bases and planetary defenses there only as a last defense when no fleet is available? Feels a bit of a waste to spend all that metal (star base) and upkeep (plan. def.) on static defenses that, against mobile attackers, are fundamentally at a disadvantage.

Combat is not triggered automatically - either you or the AI has to choose to attack.
If the AI doesn't like the balance of power it will just sit there blockading the system, and you have to attack if you want to get rid of the fleet.

(Pirates and monsters always attack, regardless of their chances.)

[Noyyau]

Interesting. The AI does seem timid at times, choosing to retreat or not attack at all more often that I would.
I wonder then if it would be possible for me to park a sizeable fleet in an enemy system, refrain from attacking (and assuming the AI doesn't have sufficient forces to want to attack me either), and just wait for a crowded planet to revolt from starvation anger, without having to bombard the place and invade the hard way (thus avoiding damage to infrastructure and dead colonists).
I'll try this in the next war.

[Arioch]

Interesting. The AI does seem timid at times, choosing to retreat or not attack at all more often that I would.
I wonder then if it would be possible for me to park a sizeable fleet in an enemy system, refrain from attacking (and assuming the AI doesn't have sufficient forces to want to attack me either), and just wait for a crowded planet to revolt from starvation anger, without having to bombard the place and invade the hard way (thus avoiding damage to infrastructure and dead colonists).
I'll try this in the next war.

Yes, it's possible, but if the planet successfully revolts they'll become independent; you won't automatically gain control.

[gaerzi]

-when exploring an unknown star system and finding there hostiles (pirates or star harpies), the message is "Attacked at [STAR]" and the fighting option is "defend". I suppose this is to give the scouts a chance to escape, as by being "defender" they get to move first.

Turn order is by faction, not by role, defenders don't necessarily move first.

[Noyyau]

Spoiler: show

Interesting. The AI does seem timid at times, choosing to retreat or not attack at all more often that I would.
I wonder then if it would be possible for me to park a sizeable fleet in an enemy system, refrain from attacking (and assuming the AI doesn't have sufficient forces to want to attack me either), and just wait for a crowded planet to revolt from starvation anger, without having to bombard the place and invade the hard way (thus avoiding damage to infrastructure and dead colonists).
I'll try this in the next war.

Yes, it's possible, but if the planet successfully revolts they'll become independent; you won't automatically gain control.

Right, they do become independent. Though if it's a former planet of mine with a population still mostly of my own race, that should make things easier to establish contact and then annex them peacefully, right?
Haven't had the time to test a blockade yet, though I have earlier peacefully annexed an independent colony.

Spoiler: show

-when exploring an unknown star system and finding there hostiles (pirates or star harpies), the message is "Attacked at [STAR]" and the fighting option is "defend". I suppose this is to give the scouts a chance to escape, as by being "defender" they get to move first.

Turn order is by faction, not by role, defenders don't necessarily move first.

Who gets the first combat turn then?

[Arioch]

Right, they do become independent. Though if it's a former planet of mine with a population still mostly of my own race, that should make things easier to establish contact and then annex them peacefully, right?

It depends on how the new morale/reputation works out... I think there's a random element, and if they're really angry about being starved, some of that may come out against you... but most likely you'll be able to annex them after having an agreement for a time.

-when exploring an unknown star system and finding there hostiles (pirates or star harpies), the message is "Attacked at [STAR]" and the fighting option is "defend". I suppose this is to give the scouts a chance to escape, as by being "defender" they get to move first.

Turn order is by faction, not by role, defenders don't necessarily move first.

No, the defender always moves first in tactical combat.

And yes, we did this to give scouts a chance to escape.

[sven]

Turn order is by faction, not by role, defenders don't necessarily move first.

No, the defender always moves first in tactical combat.

My guess is that gaerzi may have read the Lua source files for defining fleet initiative values. What's unintuitive about the low-level rules there is that "fleet initiative" is actually not used to determine which fleet moves first in a tactical battle (as any D&D player might expect). "fleet initiative", as it's used in the source code, is actually a concept that's used to determine whether or not it's possible to interrupt other player's fleet attack actions by starting one of your own. So, for example, if you and the Phidi are both above a Gremak planet, and the Phidi decide to attack that planet, is it possible to preempt the Phidi's attack by attacking the Gremak first yourself? Whether or not that option pops up is determined by "fleet initiative" -- but once the battle starts, the rule is always a simple "defender moves first".

("Fleet initiative" is as complex a thing as it is largely because I tried to setup the low-level fleet encounter rules in such a way that the game could eventually support multiplayer.)

[Noyyau]

Thanks for clearing that up.