Cargo unpacks files with too restrictive mode (breaking multi-user shared cargo registry)

I share cargo home directory between multiple user accounts and want to use cargo install from both uids. For this I want all Rust-related things to be group-writable.

But despite of umask is 0002 (new files are group-writable by default) and all directories have mode g+rwxs, some files unpacked by Cargo get usual boring mode 644, preventing clearing directories from other user later.

For example, now I see

drwxrwsr-x 6 rust rust 496 Dec 22 20:12 .multirust/toolchains/nightly/cargo/registry/src/github.com-1ecc6299db9ec823/clippy-0.0.104
-rw-r--r-- 1 rust rust 24K Dec 17 03:28 .multirust/toolchains/nightly/cargo/registry/src/github.com-1ecc6299db9ec823/clippy-0.0.104/CHANGELOG.md

Why files inside the clippy-0.0.104 directory get restrictive permissions when everything else is group-writable? Should Cargo avoid walling non-security-related files against other users when umask is explicitly configured not to do so?

Start with the cargo install path that unpacks registry archives and inspect how extracted file modes interact with the process umask. Reproduce the shared-registry case with umask 0002; done means non-security-sensitive unpacked files retain group-writable permissions and the behavior is covered by a regression test.