nx_emit_guard.nx

nx_emit_guard.nx -- the ONE set of guards every emitter CLI in this lane uses (rule 15: written twice is once too many, and these encode a LAW rather than a convenience). ★WHY: an emitter that writes a SET of files can fail in three ways that all LOOK like success -- 1. an unchecked sys_mmap returns null, so every subsequent write goes nowhere; 2. the emitter produces a technically-valid but empty page (a few dozen bytes); 3. individual writes are checked, but nobody asks afterwards whether the SET actually exists. (3) is the one that bit this lane: refine's per-file writes were fail-loud, yet a run that produced zero files still printed a success envelope, because nothing verified the set. A tool that emits a set must PROVE the set before it claims success. Dependency-light on purpose (nx_syscalls only) so any emitter can compose it without dragging a page kit in. license_tier: ORIGINAL