this is super minor, and i've seen this in human code plenty of times, but this is the norm of this app verging on being formal code style.

so you have a file reading tool, you need to declare what kinds of file extensions it supports. that's very normal. claude code takes the interesting strategy of defining what extensions it doesn't read. that's also defensible, there are a zillion text extensions. i've seen strategies that just read an initial range of bytes and see if some proportion of them are ascii or unicode.

where does this get declared? why of course in as many places as there are rules. hasBinaryExtension() comes from constants/files.ts, isPDFExtension() comes from utils/pdfUtils.ts (which checks if the file extension is a member of the set {'pdf'}), and IMAGE_EXTENSIONS is declared in the FileReadTool.ts file.

of course, elsewhere we also have IMAGE_EXTENSION_REGEX from utils/imagePaste (sometimes used directly, other times with its wrapper isImageFilePath), TEXT_FILE_EXTENSIONS in utils/claudemd.ts. and we also have many inlined mime type lists and sets. and all of these somehow manage to implement the check differently. so rather than having, for example, a getFileType() function, we have both exactly the same and kinda the same logic redone in place every time it is done, which is hundreds of times. but that's none of my business, that's just how code works now and i need to get with the times.