Are we to simply guess and just hope we've interpreted the scene with the same intent as the Director?
Yes. Exactly.
That's part of the process, part of what makes a director and a composer feel like "kindred souls" who share a similar outlook and can have a productive creative relationship. When they feel like you get it without being explicitly instructed what to do. Best-case scenario is when they can describe how they want the score to relate to the whole arc of the story, slowly revealing more and more of the central theme while nodding to the various characters and plot lines, and refer to other music in terms of the emotions they evoke. Worst-case scenario is when they don't have the abstract verbal skills to describe what they need much beyond, "I'll know it when I hear it."
I rarely have hours-long conversations about how to approach a scene, and usually there's not even all that much back-and-forth over the course of days and multiple revisions etc. That's when it starts to feel like pulling teeth, like maybe this composer just doesn't get it, like maybe we got the wrong guy.
An example of a one-minute conversation that worked: A sentimental scene, tender emotions, might even be a final goodbye before one character dies or goes away forever, can't tell because I haven't seen the whole film yet. No idea what's going on, it's just an audition cue. Temp score is in place and sounds lovey-dovey, but my first impression that I blurted out to the director was, "This temp makes it seem like these two are in love, but that feels wrong. Like it needs tender emotion but more like they're brother and sister saying goodbye for the last time or something, not like they're going to get married or whatever." Director's response: "Exactly. See what you can come up with." Done. Took less than a minute to talk that one out.
An example of a conversation that lasted a week and didn't work: Thriller / tension film, people double-crossing each other, lying, sneaking around, the whole works. But subdued and tense, not epic war-drum beat-downs, and with a high-tech sheen because they're hacking computers, swiping fake ID badges to gain entry to restricted facilities, etc. So I take a swing at it - nope, it's "too energetic and percussive and pointy somehow". Okay, take another swing. Nope, this one "still feels too active or bright or something". Okay, damn... third swing. Now the director's running out of words to describe how much he doesn't like what I'm laying down, it's just "Still not the right vibe, man, I dunno...".
In desperation, sitting with the director in the edit suite, I say, "Sounds like what you mean is something like this:" and I start singing and mouth-beat-boxing along to picture, basically imitating James Newton-Howard's amazing score to "Michael Clayton" - those tension cues as he's driving upstate. I say, "You know, kind of a Michael Clayton vibe?" And the director goes, "Exactly! That's what we had in the temp!".
But I had never heard that temp. Due to them previously hiring a composer who I was supposed to be replacing, the only temp I had ever heard was that composer's failed attempt - and nobody ever remembered to play me their original temp, the one that the network had loved, the one that helped the pilot get a series order! All I had heard was the "wrong" music from the guy they wanted to fire, and I was operating under the assumption that this was as close to "right" as they had ever gotten, when in fact it was even further away from "right" than their original temp had been! When the post supervisor found out that the editor and show runner never went all the way back to the original temp (that everyone had loved) she was beside herself - to her this was a total failure of production logistics! Aka: how not to do it. And nobody thought to mention "Michael Clayton" to me, or had the communication skills to describe the desired result as "muted, subdued, and subtle, but still tense and propelling the scene forward." - which is how I described what I was about to start singing in the edit suite, that made the director say, "Yeah, that's what it needs. What would that sound like?" and so I started beat-boxing the Michael Clayton cues.
When I finally got to "So... like a Michael Clayton vibe?" I was like, "That's all you needed to say. Just say the words Michael Clayton and I know exactly what you mean." (Not that I could actually pull it off, but at least I'd have known what they meant.) In the end, it was such a struggle to get to that point that I was like, "Man, it shouldn't take us four tries to get it right, maybe I'm not your guy." And as it turned out I was not their guy - maybe not entirely because I had the wrong music, but also partially because they had a hard time knowing / deciding / explaining what they wanted, and we didn't have enough in common that I was able to read their minds well enough.
So, being able to read the minds of the directors / producers / writers / actors and "get the vibe" even if you don't know the entire arc of the story and where a given scene fits into that arc, is going to be a part of the skill set. You won't always, or even often, be operating off your own partially-informed guesses - but it will happen eventually. Maybe it will be in season five of a series, as it's winding down, show runners are being swapped in and out, and people are looking exhausted and operating on auto-pilot - and maybe it will be on a scene that nobody's really paying all that much attention to because they have bigger fires to extinguish. But when you get it right with little to no direction, and the show runner says, "Wow, you killed it on that scene. Really made it work better and helped it feel as important as it should have been. Sorry we kind of glossed over that one in the spotting session, good job though." - that's when good guessing becomes a valuable skill.