How should I interpret an end repeat barline without a corresponding start repeat barline?
I was expecting to see a few bars delimited by corresponding start and end repeat barlines, but in this piece I encounter the end repeat barline after bar 8 but there is no preceding start repeat barline.
the barline after bar 8 is a combined end / start repeat.
The piece is a Frank Bridge Miniature piano trio - a genre whose written music I am not familiar with, although I expect repeat barlines mean the same in any genre.
the final barline of the piece is not a repeat barline and there is no “Da Capo” instructions at the end.
Once one reaches a repeat sign, one returns to somewhere. In the absence of a reverse repeat sign, there's only one place to return to - the beginning. That's all there is to it. It's pointless to have to put that reverse repeat sign in at the beginning. The only time it's needed is if there's an anacrucis, in which case, the reverse repeat will come after that anacrucis, just where it's needed.
Sometimes you will see an initial repeat barline at the start of a piece, but it's more commonly omitted because it is unnecessary. When there is no initial repeat barline, a final repeat barline means go back to the start.
Both of the examples below mean the same thing, (but arguably the first one is nicer to look at):