You don't need to allocate here. In order to avoid leaking, you just need to declare the zval and then pass a reference, PHP will handle allocation

var zval C.zval

switch v := value.(type) {
	case nil:
		C.__zval_null__(&zval)
	case bool:
		C.__zval_bool__(&zval, C._Bool(v))
	case int:
		C.__zval_long__(&zval, C.zend_long(v))
        case ...

When running PHP in debug mode (built with --enable-debug like in the dev.Dockerfile) you should see something like this when there is a leak between requests:

Last leak repeated 2 times
=== Total 3 memory leaks detected ===
[Fri Aug  1 21:58:55 2025]  Script:  '-'

It's now updated. Thanks!

you should see something like this when there is a leak between requests

Should you see this in the Caddy console when running in worker mode for example?

You'll only see it when php shuts down. So you won't see it while the worker is running.