The collections pass

List, HashMap and String rounded out together, a HashSet added, and memmove beside memcpy; chosen by the user on 2026-10-21.

A method that needs more of the element than the container does is a trait’s, as Sort already was (18.70), since a method cannot bound its type’s parameter: Search<T> (contains, index_of) for a List of Eq elements, Extend<T> (extend, insert_slice, fill) for Copy ones, and Eq and Hash on the List itself. A missing bound says which trait and which bound.
Absence is a pointer, as HashMap::get’s already was (§9.1): first()/last() return ^T, null on an empty list, so xs.last() or return reads as a lookup does.
Looking up a String key by str is a trait implemented for HashMap<String, V> alone — StrKeys<V>: get_str, get_mut_str, contains_str, remove_str — and StrSet for HashSet<String>. Chosen over a Borrow trait, which would be a promise nothing checks that two types hash alike, and over overloading, which 18.5 rules out (T-0043).
HashSet<T: Hash + Eq> is a HashMap<T, bool> underneath: the same table, one byte a slot for values that say nothing.
A runtime str reaches C through a String: let owned = String::from(name) then owned.as_cstr(). No CString type; the String already keeps a zero after its bytes. Passing String::from(name).as_cstr() straight to a call is fine, since the String lives to the end of the statement; binding that cstr with let is not (T-0006).
memmove(dst, src, bytes) joins the placement primitives (§14.3): an overlapping copy, unsafe as memcpy is. List shifts elements with it when T::is_trivially_copyable and one at a time otherwise (T-0042).
hash_combine relies on plain + wrapping, which 18.63 promises; it is not rewritten with wrapping_add, which would imply plain + might not wrap (T-0044).

Two follow-ups, the same day (r68), from what writing this exposed, fixed at the user’s word (“fix the issues you found”):

An operator reads through a reference to a number, bool, char, str or enum (§5.2), as an argument already did: x > 2 on a &i32. A retain predicate takes a &T and compares it on nearly every line, so without this the new API was awkward to use (T-0079).
Keeping a view of a temporary is an error, DZ0407 (§6.5): let c = String::from(name).as_cstr() compiled and read freed memory. The view is followed back through receivers, fields, indexes and slices only, never into a call’s arguments, and a value that needs a drop is no view, so Path("a") / "b" is not one (T-0078).

Spec: §5.2, §5.3, §6.5, §14.2, §14.3, §14.4.