Documenting this for other poor unfortunate souls, since I couldn't find anything when I first searched "hp stream 11 bootloop."
After a month of disuse, I picked up my HP Stream 11 (specifically model 11-d077nr.) On this machine I had installed Debian with grub-efi. Due to sitting so long without a charge, the CMOS had an invalid checksum and had to be cleared. Unfortunately, this resets the SecureBoot enable value to true. More unfortunately, instead of giving me an error on startup saying that it was trying to boot unsigned code, it just sat in a restart loop, showing only a black screen before restarting, indefinitely, not responding to the escape key for the menu. The boot loop occurred so fast I wasn't really sure if the firmware wasn't somehow corrupted and the machine munged beyond recognition. If a pre-EFI PC had displayed these symptoms, I would've assumed it had a hardware fault.
The solution was fairly straightforward; I just needed to boot it off of signed boot media. I had retained the recovery flash drive I had created from the OEM image when I first got it. I plugged it in, and lo and behold, I got an HP logo, and was able to hit escape to bring up the system menu and disable SecureBoot.
Not a particularly difficult troubleshooting session, but it would've saved me the mild anxiety of assuming it had been bricked if I could've found this in 2 seconds of Googling.
As a positive side-effect, looking at the maintenance manual for the HP Stream 11, I noticed that the wifi card that had been flaky for me was just one possible supported configuration of the hardware, and that it was not, as I had assumed, soldered on to mainboard. So I have an Intel dualband card coming in the mail to replace the single-band Realtek that mine shipped with.