nx_libcheck.nx

nx_libcheck.nx -- DUPLICATE-LIBRARY DIVERGENCE DETECTOR. The instrument that would have caught BOTH defects that cost this session real time (seq1423 dual-copy, seq1437 silent revert). THE INSIGHT: when a library exists in two directories, THE COPIES ARE EACH OTHER'S CONTROL. Nothing else needs to be known about them. If they are byte-identical the tree is coherent; the moment they differ, EITHER someone edited one copy and forgot the other (seq207 dual-copy -- organs under runtime/ resolve one, organs under _hdl_build/ resolve the other, so half the ecosystem silently keeps old behaviour) OR one copy was reverted underneath you (seq48/132/140 -- a sibling ships an old lib into buildroot and the NEXT BUILD STILL SUCCEEDS, shipping the old behaviour with RC=0 and no diagnostic anywhere). Both are invisible at build time. Both are one hash comparison away from being obvious. FAIL-CLOSED AND DATA-DRIVEN: divergence is a FAILURE by default. Some same-named files are legitimately DIFFERENT ORGANS -- _hdl_build/nx_fs.nx is a coreutils multitool while the live nx_fs is nx_fsops -- so the exceptions live in a CONF (rule 11), never in this code. An unlisted divergence exits 3. A conf that cannot be read simply means zero exceptions, which fails LOUDER rather than quieter. Run it BEFORE a build that touches a shared lib. Cheap enough to run every time. EXIT: 0 all duplicates identical (or expected) - 2 usage - 3 UNEXPECTED divergence - 4 no duplicates found license_tier: ORIGINAL No hw writes (Rule 26).