Rust frontend — borrowed slice type (&[T], generalized &str)

• Type: feature — Track A
• Status: backlog
• Owner: —
• Opened: 2026-07-03
• Umbrella: [[feature-rust-frontend]] — sub-ticket 8/12. Depends on [[feature-rust-frontend-skeleton]].

What it does

&str (ptr+len over string data) is trivial — reuses AnsiString's existing length-prefixed layout read-only. The general case is the actual gap: &[T] for arbitrary T needs a non-owning ptr+len view type. Every existing PXX length-prefixed layout (AnsiString, dynarray) is heap-owning/refcounted — a slice borrows into someone else's storage (a stack array, part of a Vec, etc.) and must never free/refcount it.

Scope

• New value-type shape: { data: Pointer; len: NativeInt }, no heap header, no refcount touch on copy/drop.
• Bounds-checked indexing by default (matches Rust); unsafe indexing (get_unchecked) skips the check — see [[feature-rust-frontend]]'s unsafe-block scope, already covered by PXX's existing raw-pointer support.
• Slicing syntax (arr[1..3]) produces a slice value pointing into the original storage, not a copy.

Acceptance

• A slice over a stack array, a Vec<T>, and a string literal all produce correct ptr+len values; indexing and iteration work; no spurious free/refcount on scope exit of the slice binding itself (only the underlying owner frees).
• Bounds check fires on out-of-range index outside unsafe.

Log

• 2026-07-09 — MINIMAL subset landed on master (Track R ports-back pass, commit bbd15a52), WITHOUT the shared tySlice machinery this ticket scopes: &a[lo..hi] over fixed arrays as an auto-registered __ptr+__len UClass (the Zig frontend's representation), s[i] read/write via raw i64 pointer math + AN_DEREF, s.len(). Locals only — no slice params/returns, no &str, no re-slicing. The full ticket (a real non-owning view type through the ABI) remains open and is exactly the AST/IR-work upscale case experimental/README.md describes.

• 2026-07-03 — split from [[feature-rust-frontend]] umbrella at ticket-craft time. No code written yet.