Hi Andrew, hi Aaron,
Yep (also for future archive searchers) I can confirm that the right margin overrun results from the Lily default that glissando aren't breakable, as Aaron identifies.
It should be enough to include just ...
\override Score.Glissando.breakable = ##t
... to prevent this one particular instance of right margin overrun.
There are, of course, other conditions that can also cause right margin overrun. Jean Bréfort pointed to barline-crossing durations earlier in this thread, which can also cause right margin overrun. If you *want* barline-crossing durations (complexism or music before 1600) then you need to remove Lily's Forbid_line_break_engraver from every voice context in which barline-crossing durations occur. Something like ...
\context {
\Voice
\remove Forbid_line_break_engraver
}
... does the trick for all voices in your score.
Andrew, if you're engraving a lot of complexist music, I suggest removing the Forbid_line_break_engraver as a matter of course.
Trevor.