Alright, this is a long shot, but I really would like to get my data off of my old, soft-bricked phone.
It's a Nexus 5 (running Android 6.0.1), which has never been unlocked or rooted. It gets stuck on the spinning circles that appear after the Google logo (the ones that normally become the Android wordmark). What I do have is USB debugging enabled, an authorized private key for that debugging, a Windows 7 system, access to a MacBook, and access to a variety of... hardware tools at my disposal. ADB commands work fine at whatever point in the boot process that it reaches (e.g. adb shell, logcat). Stock recovery also runs, for whatever good that is (apparently nothing; what's even the point of being able to "Mount /system"?).
I was simply scrolling through my miles-long Watch Later playlist in the official YouTube app when the system suddenly rebooted. When it finished rebooting, the (stock) launcher and Google Play Services would continuously crash unless in another app (only accessible via the middle/app history button). I brought it to my workstation intending to do diagnostics on it, but I must have hit the lock button or something on the way over, or it otherwise turned off on its own. Since then it has not made it past the aforementioned point in the boot sequence.
The logcat output I've retrieved is located here. I'm scared that it may be hardware, or at least a corrupt filesystem.
I've scoured the net and all resources I find talk about how to get data off when either having root, an unlocked bootloader, a system with a working UI and Activity Manager and Package Manager, or just a custom recovery. I have none of those things. Anything that does mention a situation similar to mine gives a single option: full data wipe caused by unlocking the bootloader.
While I accept that it was foolish of me for thinking stock would be "less risky" than custom, I remain optimistic that, if it actually is a software issue and not a hardware one, there may still be some way out there way of getting everything off of here. This is a device that's rocking a relatively outdated version of Android. I'm interested in any way I can get my data off here, even if it's more black hat than not.