loopform(hints): detect up to 2 assigned vars in loop body (no break/continue) and emit LoopCarrier hint; add smoke for two-vars case

tools/test/smoke/mir/hints_loop_carrier_two_vars_smoke.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+root=$(cd "$(dirname "$0")"/../../../.. && pwd)
+bin="$root/target/release/nyash"
+src="apps/tests/macro/loopform/two_vars.nyash"
+
+if [ ! -x "$bin" ]; then
+  echo "nyash binary not found at $bin; build first (cargo build --release)" >&2
+  exit 1
+fi
+
+export NYASH_MIR_TRACE_HINTS=1
+
+out=$({ "$bin" --backend vm "$src" 1>/dev/null; } 2>&1 || true)
+
+# Check the LoopCarrier hint contains both variable names (order-agnostic)
+echo "$out" | rg -q "\[mir\]\[hint\] LoopCarrier\((i,sum|sum,i)\)" || {
+  echo "[FAIL] missing LoopCarrier(i,sum) hint" >&2
+  printf '%s\n' "$out" | tail -n 80 >&2
+  exit 2
+}
+
+echo "[OK] MIR hints LoopCarrier(two vars) trace smoke passed"
+