Koru Standard Library: Foreign — host-owned identity registration The airlock, not a room. `std/foreign:struct(File) { path, handle }` registers a concept Koru does not own: the bytes live in the host (Zig, JavaScript), Koru mints only the name. Fields are bare names — presence claims, never types. Koru checks what it owns (does `File` have `path`); the host checks what it owns (is `path` a valid spelling there). Deep typing a field (`path: []const u8`) is refused loudly: that road ends in a Koru-side Zig grammar, version drift, and the subset-parser tarpit. What this buys is Koru-layer diagnostics for host concepts: a deref of an unregistered field fails here, in Koru's voice, instead of leaking to the backend compiler. What it never buys: derivation. A foreign entry grows no container, feeds no proto field, merges with nothing — the host owns the arrangement and Koru may not project from it. Deliberately ugly. Every `std/foreign` line is searchable host debt; a clean word would normalize the door. RULED 2026-09-04 (frag-type-system-design, module rung): inspection-only, forever — any verb beyond name, list fields, map facets reopens the ruling loudly.