A melisma spanning a system break draws two extender segments, not one continuous line, and no hyphen

If the notes under one melisma syllable straddle a system break, the extender is drawn as two pieces: one running to the end of the first system, one resuming at the start of the next system to the melisma's actual last note. No hyphen is used, since a hyphen is reserved for a hyphenated word break, not a melisma — this distinguishes it from lyric-hyphen-system-break.

Renderer either draws nothing at the outgoing system's edge (melisma silently appears to end early) or incorrectly inserts a hyphen glyph there, conflating the melisma case with the hyphenated-word case.

Gould; Read.

This rule needs the notated content and the rendered result together — the score says what should happen, the page says whether it did.