Stable type identifiers: a missing piece for crABI and export

ParaDevOne:

there is any prior work on stable type identification that isn’t directly tied to ABI compatibility.

Then maybe I'm misunderstanding your goal:

ParaDevOne:

The use of stable type signatures is critical to having Rust-to-Rust dynamic linkage, as the absence of stable type information means that any dynamic linkage would require unsafe FFI in Rust

How do you reach that goal without tying such identifiers to the ABI? Your proposal as is doesn't reach the goal because it doesn't protect against UB from a mismatched ABI, so it must also be unsafe.