The first thing to note is that the opening para in RRG 3.2.10 (pg 26) should read (my bolding):
"If a player controls at least one ready unit in a battle at the beginning of his combat turn, and there are no enemy units at the planet, the battle ends and the player controlling the only unit(s) at the planet is the winner of the battle."
This has been confirmed with the design team, and keeps this rule in sync with the flowchart's 3.2.10 box, plus the LTP and its examples.
Note that when this battle-end check succeeds, the unit that would be about to attack does NOT exhaust. A unit exhausts as part of an attack, but that attack never actually initiates - the battle ends before it attacks. Also note that units do not automatically ready when a battle ends - that only happens if a combat round ends and the battle is to continue.
The design team have confirmed that when a battle ends, the sequence is:
1. Battle Ends
2. Winner/loser is determined
3. Winner triggers battle ability
This means that any "until the end of the battle" duration will be over before the battle ability triggers (and even before a player officially wins/loses the battle). It also means that interrupts/reactions (forced or otherwise) to each part of the sequence would be used before the next part of the sequence, e.g., you react to the battle ending before the battle ability can be triggered.
The best way to get a handle on how a battle ends is by slavishly following the RRG flowcharts. Some examples:
Example 1: My lone unit destroys the last enemy unit with its attack. The combat round end-check succeeds (there are no ready units). I refresh my unit. A new combat round starts. At the start of my next combat turn, the battle ends.
Example 2: I have 7 units. 6 are exhausted. My 7th unit destroys the last enemy unit with its attack. The combat round end-check succeeds (there are no ready units). I refresh all my units. I have the chance to retreat some of them to HQ (these would revert to an exhausted state). A new combat round starts. At the start of my next combat turn, the battle ends.
Example 3: I have 7 units. My third unit destroys the last enemy unit with its attack. At the start of my next combat turn (my 4th unit is about to attack), the battle ends.
Example 4: My warlord and a unit (who arrived exhausted during the commitment) are at a planet with no opposing units. At the start of my warlord's combat turn, the battle ends.
There is an action window before and after every combat turn. If you have no units at a planet but you want the battle to continue, you'll need to execute an action in the action window that opens/closes just before your opponent's combat turn in which the battle-end check will succeed (at the latest) - either to allow you to place a unit at that planet, or remove all your opponent's units from that planet, thus making the battle-end check fail at the start of his combat turn.
(Note: If a combat turn starts and there are no units on either side, the battle immediately ends in a stalemate.)
If you're going to add a unit though, you'll probably want to do that in an action window just prior to what would otherwise be your last combat turn, so that you'll get a chance to attack with it (as opposed to the action window just prior to your opponent's combat turn, in which he'd attack your unit first).
Lastly, a combat turn does not equate to a combat action.
- A combat turn is the option to attack or pass.
- A combat action is an action that can only be performed in an action window during the combat phase.