nx_self_host_candidate_verify.nx

nx_self_host_candidate_verify.nx -- the TEAM's capability to drive codegen integration itself: BUILD a candidate compiler from source, then VERIFY it. This is the machine the team turns to change codegen (e.g. widen nx_x86_regalloc) safely, with no human at a shell: 1. SELF-HOST: the pinned known-good compiler compiles the compiler's OWN source (runtime/nx_compile_x86.nx + imports) -> a CANDIDATE compiler ELF. This is the bootstrap step; if a codegen-source change is bad, it shows up here. 2. DIFFERENTIAL VERIFY: run a corpus of self-verifying programs through the known-good AND the freshly-built candidate, and assert IDENTICAL behaviour. A miscompiling candidate DIVERGES and is caught -- the known-good stays pinned (Warden); only an all-green candidate is eligible for promotion. Built non-destructively: the candidate lands in /tmp; nothing protected is touched. With the source UNCHANGED, the candidate must behave identically to known-good -- proving the build+verify pipeline end to end so the team can then plug a real regalloc change into the SAME machine. Known answer: exit 0.