D002 - Edition 2024, with a pinned build toolchain

Status: decided Date: 2026-08-19

The workspace uses edition 2024 with an MSRV floor in Cargo.toml, and the build toolchain is pinned separately in rust-toolchain.toml.

Why: edition 2024 warns on unsafe_op_in_unsafe_fn and requires unsafe extern blocks, which match the unsafe discipline the lints enforce. The toolchain a build uses and the oldest toolchain the code supports are different facts, and conflating them produces CI failures nobody can explain.

Rejected:

• An unpinned toolchain: host and CI compile with different compilers.
• One number for both: a toolchain bump silently raises the supported floor.