[zayeem06]

open_new_blocks stores the opening fence length in a uint8_t and clamps it to 255, so a fence of 256 or more backticks is closed by any line of 255 backticks, where the spec and commonmark.js keep the block open. That breaks the commonmark round trip: a code block containing a 300 backtick line followed by <script> is rendered with a 301 backtick fence, and parsing that output back ends the code block at the 300 backtick line and turns the script into a live HTML block. Widen fence_length to int and drop the clamp; the union is still 16 bytes so sizeof(cmark_node) stays at 104, and an api_test case covers the 256/255 case.