nx_codegen_improve_loop.nx

nx_codegen_improve_loop.nx -- the TEAM's autonomous codegen-improvement loop: the one machine that drives a codegen change from source to a governed, MEASURED promotion decision, with no human at a shell. This is what "get the team there in partnership till they can do it themselves" means concretely. 1. SELF-HOST the candidate compiler from the compiler's own source. 2. VERIFY differentially vs known-good on a corpus (no miscompile). 3. MEASURE race the SAME kernel compiled by candidate vs known-good: checksum must stay byte-identical (correctness) and we read cycles for both (the win, or a regression). 4. GOVERN the crew council ACTs only if verified AND not slower; a miscompile or a regression is ESCALATEd (rolled back). Run here on the IDENTITY candidate (current source) it proves the loop end to end + measures the baseline; a real regalloc change plugs into step 1's source and the SAME loop decides. Non-destructive (candidate in /tmp; known-good pinned). Known answer: loop runs, candidate verified + not slower -> council ACT, exit 0.