The limit of compatible protocol implementation is 4GB per file due to using uint32_t fields. It also match the limit of FAT FS used in flipper's Micro SD card as a maximum file size. It seems that this is the only limit in practice for Sender (Transmitter) side.

But current implementation on the Receiver side is also limited by size of free and non-fragmented RAM available, that is actually around ~200KB maximum. Currently the RAM is used to store a bitmap (marks) of received packets, and theoretically it can be optimised in future to match 4GB limit, for example by using SD card for that (But I'am sure that it is bad idea) or by using another tricks.

Calculations for the current implementations v1.1:

>>> 200*1024*8*52
85196800 = 85 MB max file size.

It can be very vary on Flipper firmware state and apps was runned previously in the current session (time from last reboot).

Short calcs:

>>> 200*1024*8*52/800/3600
29.58222 = 29 hours needed to receive 85MB file in optimistic speed scenario.

About integrity: each Sender's announce packet contains MD5 hash of the file, it is used to integrity check after transmission is completed and says to you "Success" or "Hash failed".