asset precompile, not noticing when images change

[Jonathan Rochkind]

So I remember that special logic by @ndbroadbent for asset compilation,
that tried to only recompile assets when they really needed it, I think?

I forget if that ended up being Capistrano-specific, or built into
rails, or what?

In whatever version of that code I'm using, it does not seem to notice
when a referenced image has been changed, thus requiring a recompile.

For instance, I have an .scss file with:

background:image-url("something.png")

So this gets compiled to one big CSS file, that includes, among other
things:

background: url(/assets/something-9348934839434.png)

Now, on disk, something.png gets changed to a different file.

So, the CSS needs to be recompiled too, so it will include the right
url() to the proper current fingerprinted filename.

However, the CSS is not recompiled.

So there's a bug or faulty design somewhere... but I've actually lost
track of where the heck this logic lives now, and where to look to
investigate it further, or report an issue.

Any tips?