Add [lints.clippy] unwrap_used = "deny", expect_used = "deny" plus a tracked pre-commit hook running `cargo clippy --lib -- -D warnings`. Library code may not hide a panic behind unwrap/expect; panic!/unreachable! stay un-linted as the explicit sanctioned form. Gate is the library target only — tests and examples are not gated. A fresh clone must run `git config core.hooksPath .githooks` to enable the hook.