Technicalities of deficit with no scale change?

Hello, I'd like to start off by saying that I am thrilled with the results I've been getting on the nutrition and body change fronts. Couldn't be happier there.

This question is out of pure curiosity as to what is physically happening to my body on an ongoing basis as I continue to eat on a slight calorie deficit, while maintaining my scale weight. To be clear I have never had a lot of/any scale weight to lose (2.5 kg absolute max, although I couldn't care less if that ever happens).

- 5'8" (173cm) at 132 lbs (60kg), just fine for me.
- Used to be skinny fat, but almost exactly 2 months ago, I completely overhauled my nutrition and fitness habits. Was ~23% BF, now probably around 21.5% based on comparing with example images.
- Work out for an intense 1 to 1.5 hours, 6 days a week (P90X, so mixture of strength and cardio)
- Have been weighing and eating mostly whole, nutritious foods, loads of veggies:
- at least 100g of protein a day,
- at least 35g of fibre a day
- about 2.5L of water a day.
- I have my daily calorie goals aimed at about a 250 calorie deficit, which *theoretically* is 0.5lb/week steady weight loss. That is, my Fitbit-calibrated TDEE is typically 2100 calories on a work day (1700 sitting still on my keester for 8 or 9 hours, 400 calorie one-hour morning workout), and I gross around 1750-1850 calorie intake a day.

Let's just say that I am trying my best to do things "textbook" based on what people have had success with,and most importantly, in the healthiest way possible. And it's working great for my personal goals of being fitter, stronger, more energetic, healthier. I am noticeably losing fat from my mid-section, and have gained a bit of upper body muscle (purely beginner gains, I don't expect mass gains to continue by any means while eating on a deficit).

Questions:
As my scale weight literally has not budged week to week over the last 10 weeks (not counting daily slight +/- 0.5 fluctuations), always hovering 60.0kg, what exactly does it mean to my body to be eating at a calorie deficit at this point?

Am I losing a bunch of fat, then replacing that lost fat in a continuous fashion with the exact same weight of muscle, gram for gram (but only as much as possible given the energy my body requires from consuming body mass due to the deficit)?

What if I continue to eat at a deficit along with my current nutrition/fitness regimen over a longer period of time? Doesn't *something* need to eventually be broken down to continually feed that calorie deficit, or has my metabolism fine tuned itself for the slightly smaller amount of fuel I am giving it each day to maintain its current physical state? At some arbitrary point down the road will my scale weight actually begin to drop steadily every week (for better or for worse)?

I guess a 250 calorie deficit also isn't a huge margin of error to play with if my food weighing vs exercise calorie estimates are just slightly inaccurate and I come out even Steven with my TDEE over the weeks and months. It seems unlikely to be that error prone if it is generally on the correct side, although granted, it is really just a ballpark estimation when it comes to calories burnt doing strength training (317? 350? 403?... ). I just count 350-400 for the hour and half depending on my perceived effort and minutes spent. Is this too high an estimate closing my deficit gap?

I know my body is not some unique conundrum that manages to defy all logic, so my inquisitive, logical mind would like to understand what is happening to my body as the days, weeks, and months go by. The goal here is not to change anything (unless I've described a horrible terrible lifestyle decision above ), but just to understand how this is possible.

Thoughts or theories?

Some of you might be tempted to say who cares if I'm getting the results desired, but I'd like to think I've gotten this far by caring enough to seek out resources and thinking things through thoroughly (alliteration!). I prefer to understand instead of blindly following.