The error message:

This all worked before the re-org. No Typescript code change. Plenty of changes in package.json, tsconfig.json, etc. Any theories? Pointers on where to start looking?

It's happening during

pulumi preview

as can be inferred from the "Error serializing..." message, so it's not that the lambda itself is broken (though it may well be...).

I've worked around it for now by removing the call to fs.readFileSync() from inside the lambda, and instead passing the contents of the read file as a string via an env var. I'd still like to know what's changed, as it may be causing other subtle bugs.