_atomic_rewrite_gate.nx

_atomic_rewrite_gate.nx -- WMS-R3 gate. PROVES the generic atomic_rewrite primitive (nx_atomic_rewrite.nx) is crash-safe, with a WORKING NEGATIVE CONTROL (the old in-place rewrite) that demonstrably tears under the SAME crash point -- so the gate can actually detect failure (no false green). All four sub-tests run on real /tmp victim files (NO mocks): (1) commit_ok -- atomic_rewrite(v1) then atomic_rewrite(v2): reader sees exactly v2, NOT v1 (clean whole-file replace works). (2) crash_safe -- establish v1 on disk; a FORKED CHILD calls ar_crashwrite (stage temp + fsync, NO rename) then exits; a FRESH reader of the live path still sees EXACTLY v1, intact (the headline crash-before-commit claim). Then a real atomic_rewrite(v2) -> reader now sees v2 (after_commit). (3) neg_torn -- NEGATIVE CONTROL: a FORKED CHILD runs the OLD unguarded ar_unsafe_inplace, which TRUNCATES the live file then writes only HALF the new bytes, then exits (crash mid-write). A fresh reader sees a TORN file: neither the intact previous content NOR the full new content. If this does NOT tear, the gate is INVALID -> RED. (4) tamper_bites -- atomic_rewrite to an UNWRITABLE path (bad dir) MUST return negative AND leave the real victim unchanged (the primitive reports failure, never half-commits). pass = commit_ok AND crash_safe AND after_commit AND neg_torn AND tamper_bites Evidence -> knowledge/status/atomic_rewrite.log (ATOMICRWGATE row). SOVEREIGN: nx_atomic_rewrite (-> nx_syscalls) only. license_tier: ORIGINAL