[dannote]

The lowering restructure discussed after rc.17. Behavior changes only where generated Rust gets more precise; Figler's generated crate is byte-identical except one collect::<Vec<_>>() that now names Vec<Occurrence>.

Ownership (RustQ.Meta.Ownership). A backward liveness pass annotates every variable occurrence with what is still in use after it, following Elixir's scoping: sequence and argument order, alternative branches (case, if, cond, with), closures and comprehension bodies as repeated regions (what they capture stays live; their own variables follow the body), rebinding ending a value, and values built from another keeping it live while they may borrow (by type). Lowering asks one question, "is this the last use?", replacing the per-statement analysis, the others lists threaded through Enum/Map/MapSet, and the in-place update list in ast.ex; parameter mut now comes from the lowered Rust. Fixes the sibling gap: {Map.put(scores, …), scores} clones.

Fused pipelines. An Enum call over another Enum stage (map, filter, reject, flat_map, with_index, take_while, drop_while, zip_with, slice, take, drop, reverse, chunk_every) continues its iterator instead of collecting: .map(f).find(p), .filter(p).count().

Std method types. mix rustq.std derives 179 return types from std's source for methods on str, String, char, Vec, slices, HashMap, HashSet, and Option whose results don't depend on the receiver's type parameters; Typing uses them, so name.len() is usize and predicates get |&len|.

Desugaring (RustQ.Meta.Desugar). Map.new, MapSet.new, Enum.into into an empty collection, group_by, uniq, and with_index generators are rewritten into other Rusty-Elixir before ownership and lowering, leaving __rustq_items__/__rustq_owned__ where lowering must decide by type or ownership. Lowering accepts multi-expression blocks as expressions, and Typing types comprehensions.

Split lower.ex (4,536 → 2,907 lines) along call-graph seams into Lower.Pattern, Lower.Comprehension, Lower.Paths, and Lower.Mutability, which call back through a few documented Lower functions.

Checked: mix ci (885 tests, every fixture cargo-checked); Figler mix ci and cargo clippy -D warnings on this branch.