Char-count guards on value/id can still let multibyte or escape-heavy
inputs blow past MAX_ENCODED_CURSOR_LENGTH once UTF-8 + escape expansion
+ base64url runs. A 512-character name of 'é' (2 bytes UTF-8) or '<'
(serializes to the 6-byte '<' escape) passes the char check, mints
a ~1500-byte cursor, then 400s when handed back on the next request.
Compute the final encoded form and reject it before returning if it
exceeds the wire cap. Adds regression tests for both inflation paths.
2015bbb54a