Originally published on hexisteme notes.
A user complaint sent me into a caption pipeline: "the subtitles cut to two words in places where the sentence doesn't make sense." The fix I shipped for that complaint introduced a second bug, one word narrower and easy to miss, because the code that measured whether a line of text would fit reproduced an assumption about the text that the code drawing the line didn't share. Every test passed the whole time. I only found it by watching the rendered video.
The bug the complaint pointed at
The captioning system splits a transcript into short chunks that pop onto screen a few words at a time. The chunking function was doing fixed-size slicing — take the next N words, regardless of what came before or after. That's blind to sentence boundaries, so two unrelated sentences could land in the same chunk: loss. Today reads as one visual unit even though it's the tail of one sentence and the head of the next.
The fix was a rule set, not a single tweak:
