Unable to get app-scoped bookmark for file - OS X sandbox

To my everlasting shame, it was my fault.

Somehow in moving the project to a different machine for testing and debugging, code-signing for the Development build got turned off.

Apparently this causes things to (almost) silently fail, with no error code and only a cryptic message in the console, and no other indication that anything else isn't working properly.

Leaving this up here in case someone else mistakenly does the same thing.