It's likely the Kobold knows things like (i) where it entered the city, (ii) where it came from, and (iii) how many other Kobolds are with it.
There is a reasonable chance of know it might know those things, I agree. But it is just as likely it might not:
(i) remember where it entered the city from. People get lost and turned around in cities easily when they are not from them or moving quickly (like a kobold strike force).
(ii) depending on the location, region, etc. the names it knows things by might not be at all how the PCs would know them.
(iii) as part of an attack force, it should reasonably be able to tell you "many", but why would it know just how many there are? perhaps numbers or even their concept are foreign to the kobold culture (a stretch and more homebrew admittedly).
However, again, all this depends on just how smart the kobold is, what rank it has within its... well, ranks, etc. So, while I agree it is entirely reasonable to hope you might get such intel from the kobold, there is no guarantee what you will actually get.
I know when I DM and players capture creatures (a very common practice as I am sure you can imagine!), I run the entire gambit for how much the PCs will learn. Sometimes nothing, sometimes everything (with detailed maps!), and most the time in between.
Are you talking about a character in a RPG, or a player playing a RPG where there character is trying to buy milk, or about an actual real-world trip to the shop to buy milk?
Ok... I am going with the thought you are asking this in earnest...
It is a direct analogy. I expect (it is a reasonable assumption) that if I drive to the store to buy milk, I will be able to buy milk there. I will get there successfully, I have the money, the milk will be there, and someone will be working their to take my money in exchange for the milk. However, when I arrive and have my money, there is NO milk at the store--it is all gone. So, while it was a reasonable expectation I would be able to buy milk, I was disappointed because there was no milk and I could not.
In your situation, you wanted to capture a kobold to get information (the reasonable assumption). You developed the plan, and carried out the plan (capturing the kobold == me getting to the store), but the kobold was unable to provide you with information (no milk).
It sucks, but it happens. I did not get to just say "Well, it is a store, there should be milk," and
poof there is milk! Just like you players don't get ti decide "Well, the kobold should be able to give us information", and
poof it must be so.
The real-world activity I've been talking about is not shopping; it's playing a RPG. When I sit down to play a RPG, just as when I sit down to play any other game, I expect to be able to affect what happens in the game. As I've already posted, I'm not just turning up to have the GM tell me their story.
I understand that, but IMO I don't think you can reasonably expect every action to you take to work in your favor, do you? You don't expect every plan to work, every attack to hit, etc. right?
You affected the game by removing that kobold from the assault. You just didn't get the result you hoped for. Just like I didn't get to buy the milk I had hoped for.
How does it take away "all agency"? The player can build a new PC and jump right back in.
Because the player then knows they still don't have the agency to control their character as they wish since the DM can kill the PC off without any hope of salvation--again, and again, and again.
Random chance is certainly a factor IRL, and if a DM said "Ok everyone, each day of the game I am rolling 10d20s for each PC. If
all the d20s roll 20, your PC suffers from some horribly calamity and is killed instantly," I would laugh and say, "Sure, go ahead."
However, if a DM said the same thing but is only rolling 1d20, I would say, "No, I don't think so. A 1 in 20 chance to just "die" a random death doesn't jive" and I would exercise my right to walk away. If just a DM had other players who were ok with this idea, I hope they enjoy it.
A recurring element in some discussions on these boards is not engaging with the distinction between (i) failed action resolution and (ii) the GM just saying "no" until the players say the magic words that will prompt the GM to say "yes".
Agreed, but you don't seem to understand---or at the very least just don't agree---that you did not (i) fail action resolution. You succeeded in capturing a kobold (the action) but the resolution just wasn't what you expected. That is not failure.
Now, my proposed scenario where you learned incorrect intel or when you acted on it, it was no longer valid, seemed (correct me if I am wrong!) to satisfy you that your action resolution was not a failure because you received some intel; even though this intel was useless to you.
So, acting on no intel gained vs. acting on misleading/ incorrect intel? Which is better? You feel better in the second case?
Finally, if the DM in question pulled the same thing many times over and over, then I can see your point a bit more. Which brings us back to the original situation and my thoughts this was just the final straw---not really the inciting incident.