Make a source handler handle the result of another source handler?

The coffeescript plugin handles files ending with .coffee and turns them into files ending with .coffee.js, so I thought I could write a source handler that handles .coffee.js files, hoping it would then handle those output files, but it doesn’t work.

What’s the currently prescribed way, if any, to handle the result files of one source handler with a second source handler?

@slava @glasser Is the phases proposal separate from the batch handler proposal, each feature will work separately?