Why would the PCs be unable to anticipate NPC attacks? They live in the same universe, with the same physical and magical laws. There may be some in-game cultural constraints on NPC action, the PCs may know about that too. Eg in a Viking game it may be routine tactics to burn down the farmstead the other guys are sleeping in; in a Western it may be honourable to duel in the street at high noon whereas shot-in-the-back is murder.
Your description of players 'losing agency' reminds me of certain turtle players I've seen. But IME turtle play was far more common in 3e than any other edition; partly because it was the only edition where high level play mandated that the GM not use the RAW if the game were to be playable.
The question is really whether or not the DM can determine what the NPCs can and can't do and when, where, and how they will do it or not. Typically there are many unanswered questions about this kind of thing (speaking from experience and noting that I have a pretty detailed setting that has seen a LOT of play over 30 years). It isn't hard for the DM to come up with plausible situations where the PCs can be attacked, but do the PLAYERS really have the level of detailed information they would need to anticipate them? Generally not.
Of course it depends somewhat on the nature of the enemy. You may well be reasonably able to guess that the orc tribe will launch raids against your village and you can probably determine what orc tactics are. Orcs are fairly predictable opponents. The thieves guild OTOH? Unlikely to be very predictable at all. You better not jot out back to the loo, eat a meal you didn't cook yourself, etc etc etc. In the real world one can at least understand this sort of enemy and determine exactly what his resources probably are and decide when and where you're likely to be more or less safe. In a game, where the person organizing this opposition knows everything about you and has carte blanc to decide the details of exactly who's an informer, what sort of tools the bad guys have, etc the players will not really be able to do this.
Thus in effect the DM is probably going to say to himself something like "Hmmm, yeah, I won't mess with them in their castle because ...." and come up with some plan that HE considers plausible, but which the PCs really can't even find out about or anticipate because the plot doesn't exist until the DM invents it (IE "Oh, yeah, I know, the bartender actually owes the thieves guild 500gp, so he's going to look the other way while their guy slips poison into the character's ale"). That's the sort of thing that might logically happen, but there's practically zero chance even the most thorough DM has mapped out the entire web of relationships between NPCs and whatnot ahead of time such that the players could have their characters figure it all out.
CaW works pretty well when it is basically one-sided or the enemy is not exceptionally proactive or is reasonably limited in their means to respond. You can anticipate the orc tribe, set an ambush, foil their raid. Once you get into the level of more capable and flexible opponents it turns into more of a "what's fair" situation where the DM has almost unlimited options but will only choose to exercise some that create an interesting story. In fact at a strategic level it really becomes indistinguishable from 'CaS'.
Basically IME there's just no clear boundary between the two and rarely a hard distinction. I could certainly create settings where one or the other mode is prevalent. For instance you won't run into many downright dishonorable fights in our Alleterre campaign because its all about medieval knights and damsels, etc. There can be a few designated "dishonorable people/creatures/whatever" that you know not to count on to play by the conventions, but largely fights are fair. Clearly you could also create a Machiavellian court intrigue and backstabbing game where poisoned cups and backstabs are the rule of the day. Neither type IMHO is that close to what D&D normally is (and I note that I wouldn't use D&D as a system for either of the above settings).