Phase 21.6 — Solidification Checklist

Acceptance (all must be green on this host)
- Parser(Stage‑B): loop JSON canary PASS (no empty body; cond = Compare <, lhs=Var i, rhs=Var n|Int const)
- MirBuilder(delegate): MIR(JSON) for minimal loop contains only control‑flow ops (const/phi/compare/branch/binop/jump/ret)
- VM: MIR(JSON) for minimal loop returns 10
- ny‑llvmc(crate) EXE: returns 10

Guardrails
- No default behavior changes; all aids behind env toggles.
- Logs quiet; tags/dev traces are opt‑in.
- No llvmlite in default chain; crate backend is main line.

Canaries to run
- bash tools/dev/stageb_loop_json_canary.sh
- bash tools/dev/phase216_chain_canary.sh

Rollback
- Parser fallback in parse_loop is conservative; remove after VM/gpos fix lands.
- Keep canaries; they protect against regressions.