linear_type.nx

linear_type.nx -- runtime tracking for linear/affine resources. Phase A of the full linear-type system (EFFICIENCY_ROADMAP §3.2). Today's NishiLang has no compile-time borrow checker, so we approximate the safety benefit at runtime: an owning handle struct that tracks "has this been used yet?" + panics on double-use. Callers that adopt this pattern get the benefit immediately; the compiler-side move/borrow checker can retrofit without breaking the API later. The canonical failure this prevents: double-free / use-after- free / duplicate-consume bugs -- the same class that tonight's "duplicate main in nxc.s" + "alloca clobbered by callee-saved reuse" bugs both lived in. Linear types at compile time would reject both without a test suite. Usage: let h: *Linear = linear_new(ptr as i64, LK_FILE_HANDLE) let taken: i64 = linear_take(h) // consume exactly once linear_take(h) // -> LINEAR_ERR_REUSE Also exposes a RefCount type for when true linearity is too strict and you want shared ownership with explicit counting. Invariants: LT1 `linear_take` on a fresh handle returns its payload + 0. LT2 Subsequent `linear_take` returns LINEAR_ERR_REUSE deterministically. LT3 `refcount_clone` always succeeds + bumps count. LT4 `refcount_drop` decrements; when count hits 0, calls the user-registered free hook exactly once.