The MarkdownV2 fenced-code protection regex
r'(```(?:[^\n]*\n)?[\s\S]*?```)' made the newline after the opening
fence optional, so it also matched *inline* triple-backtick spans on a
single line (e.g. "the syntax is ```x``` inline"). _protect_fenced
then treated the inline span as a pre block, escaping backticks into an
unbalanced entity; Telegram rejected the whole message with 'can't find
end of pre entity' and Hermes fell back to plain text, dropping all rich
formatting.
Anchor the pattern to line starts (0-3 spaces indent) so only standalone
fences match, and rewrite _protect_fenced to use explicit capture groups
(opening line / body / closing fence) instead of naive [:-3] slicing,
which also fixes a doubled closing fence when the close line had trailing
whitespace.
Fixes#85381
5f7b1e2d65