Replying to myself. Changing:
if ((string) $tv['value'] !== '' && $tv['value'] { 0 } != '@') {
to
if ((string) $tv['value'] !== '' && !preg_match('%^@INHERIT%', $tv['value'])) {
seems to do the trick. I’ve only done very quick testing at this point, but ... Just remembers that a lot of people hate regex, and it’s not as fast, so this seems to work too:
if ((string) $tv['value'] !== '' && (strpos($tv['value'], '@INHERIT') === false)) {
Thoughts on that? Anybody see any reasons this would be problematic?
Second update: While I was in there I thought it’d be nice if @INHERIT allowed something like:
@INHERIT
Some extra code to add to the inheritance
I have it mostly working (with the @FILE bindings too), but I’ll test that more before I share it, since it’s late and I don’t want to look like an idiot

It does seem to work though, except that the anything extra after the @INHERIT won’t be passed on to descendants. So just the @INHERIT block actually inherits, not any extra stuff.
I’d love some feedback though. Like I said, it’s late and maybe I’m missing an obvious problem.