Increase userdata tag size from 8-bit to 16-bit

[MrDrElliot]

Hello!

I'd like to increase the userdata tag from uint8_t (255 tags) to uint16_t (65535 tags).
In Udata:

// Before

uint8_t tag;
int len;

// After

uint16_t tag;
uint16_t len;  // demoted from int to maintain struct layout

This keeps offsetof(Udata, data) == 16, satisfying the existing alignment assert. The tradeoff is len becomes uint16_t, capping userdata size at 65535 bytes, which should be acceptable for my userdata usage.

Are there any footguns with this approach? Specifically:

Are there places in the VM, serializer, or GC that assume tag is 8-bit or len is 32-bit? (beyond the obvious assertions and casts to 8 bit integers scattered about)

Is capping userdata size at 65535 bytes a concern?
Is there a preferred alternative for scaling beyond 255 userdata tags?

Thank you!

[MrDrElliot]

I have this currently implement and nothing has blown up yet, it obviously vastly increases memory usage. (Relatively)