D064 - A literal NUL byte in a source file made it invisible to grep, which hid a duplicate constant

crates/selfish-pkg/src/write.rs contained a raw 0x00 inside a byte-string literal - b"RIF<NUL>" rather than b"RIF\0". It compiles and the test passed, so nothing complained.

But git and grep classify a file containing NUL as binary and skip it silently. Every search run across this repository was quietly missing that file, which is how the duplicated IMAGE_KEY_INDEX survived: the search that would have found it could not see the file it was in. examples/decrypt.rs had the same byte.

Worth a decision entry because the lesson is not "avoid NUL bytes" - it is that a tool reporting nothing is not the same as a tool reporting no matches, and grep says nothing when it skips a binary file. Both are now the escape.