Rust 1.98 miscompiles a boxed async trait object into a null vtable slot

Sources: rust-lang issue 161441, r/rust discussion
Summary: A miscompilation marked P-critical is tracked against Rust 1.98.0 in rust-lang issue 161441. Code built with that toolchain can emit a zero-filled vtable entry for a boxed async trait object, so a call through that entry dispatches to a null pointer.
Why it matters: Safe Rust built with 1.98.0 can dispatch through a zero-filled vtable entry and segfault at runtime, so teams on that toolchain hit crashes their type system was supposed to rule out.
Follow-up: Track the point release that carries the fix and which 1.98 builds are affected.