How large can a "recovery" like TWRP be? Perhaps someone can correct my understanding.


True or false: TWRP is copied into the "recovery" directory and can be executed after reboot.
True or false: Running TWRP does not require an unlocked bootloader. (If so, why not?)
True or false: The size of a program such as TWRP is limited only by the size of the partition it is being copied into, and could be quite large.
True or false: An entire OS could in theory be run as a "recovery" if it were so desired.
False. Many newer devices utilizing the A/B partition layout don't have a dedicated recovery partition. See landing page for Google Pixel for a full explanation.
True. Certain devices have exploits that allow recovery on locked bootloaders - this kind of recovery is often referred to as "Safestrap". Do note "exploits" - most devices don't have such discovered.
True - partition size is usually the same as boot. On my Xiaomi Mi Mix 2, both are 67108864 bytes, i.e. 64MB.
True - recovery can be considered a minimal OS by itself (with complete display, input, file management subsystems). If you want to start a regular OS by booting into recovery, just flash a regular boot image (one that usually goes into boot) to recovery.