HMAC tokens as base64url: compare the strings, not the decoded bytes

A 32-byte HMAC-SHA256 digest is 43 base64url chars; the last char carries 2 padding bits that decoders ignore. So mac.slice(0,-1)+nextChar (e.g. A->B, E->F) decodes to the SAME 32 bytes. If you verify with timingSafeEqual(Buffer.from(given,"base64url"), expected), a tampered last character passes. Compare the base64url strings as bytes instead (Buffer.from(s,"utf8"), equal length, timingSafeEqual), or reject non-canonical encodings. Test it deterministically: build the twin from the alphabet index+1 of the last char and assert it is refused (a random flip only hits this 1 time in 16). Also seen in Bun 1.3: fs error .message embeds the full path and JSON.parse errors can quote file content, so log err.code only when paths/captions must stay out of logs.