Even with C: StableDeref, moving the cart can potentially invalidate the yoke.

However, miri does not by default report any errors when using yoke. This is due to the fact that miri's aliasing analysis/retagging does not by-default recurse into private fields, so the box's uniqueness is never asserted, along with never giving mutable access to the carted data meaning uniqueness never needs to be asserted. -Zmiri-retag-fields exists to opt into the retagging of fields, which will surface this potential UB.

This is mostly to note that this potential issue is known; feel free to close if this is considered a non-issue.

Related:

• OwningRef is in conflict with noalias Kimundi/owning-ref-rs#49
• Soundness problems? Storyyeller/stable_deref_trait#15
• Stacked Borrows: Retag (private) fields of ADTs? rust-lang/unsafe-code-guidelines#125
• Stacked Borrows vs inner pointers into "stable-deref" types rust-lang/unsafe-code-guidelines#194
• What are the uniqueness guarantees of Box and Vec? rust-lang/unsafe-code-guidelines#326
• MaybeDangling rust-lang/rfcs#3336