The parser is the Package Control Markdown library with pymdown-extensions,
declared in dependencies.json, instead of a vendored markdown2 -- what the
channel review asked for. The channel serves Markdown 3.2.2 to the Python
3.8 host and 3.10.3 to the 3.13/3.14 host, so the code runs on both and CI
installs the pair each host receives. A list preprocessor of our own keeps
two-column nesting, cuddled lists and fences inside items rendering as
before; the repository's own Markdown is unchanged apart from three
corrections, and the 100 KiB benchmark is 5% faster. ADR 0012 has the
numbers.

Package Control messages are down to the install note, with a test that
keeps any future one short and linked to the changelog. Open in Browser
writes a standalone page and hands it to the default browser.