diff --git a/tools/selfhost/README.md b/tools/selfhost/README.md
index 43809afa..21c0cdaa 100644
--- a/tools/selfhost/README.md
+++ b/tools/selfhost/README.md
@@ -8,14 +8,17 @@ Script
 - tools/selfhost/selfhost_build.sh
   - --in <file.hako>: input Hako source
   - --json <out.json>: write Program(JSON v0); default: /tmp/hako_stageb_$$.json
+  - --mir <out.json>: emit MIR(JSON) from source (runner path)
+  - --exe <out>: build native executable via ny-llvmc (llvmlite harness)
   - --run: run via Gate‑C/Core Direct (in‑proc). Exit code mirrors program return.
   - Env:
     - NYASH_BIN: path to hakorune/nyash binary (auto-detected)
     - NYASH_ROOT: repo root (auto-detected)
+    - HAKO_USE_BUILDBOX=1: use BuildBox for emit-only (no run/exe)
 
 Examples
 ```bash
-# Emit JSON only
+# Emit JSON only (Stage‑B)
 tools/selfhost/selfhost_build.sh --in apps/demo/main.hako --json /tmp/demo.json
 
 # Run and use exit code
@@ -23,7 +26,6 @@ tools/selfhost/selfhost_build.sh --in apps/demo/return7.hako --run; echo $?
 ```
 
 Notes
-- The script uses Stage‑B entry (lang/src/compiler/entry/compiler_stageb.hako).
+- Stage‑B emit uses either the Stage‑B entry or BuildBox（HAKO_USE_BUILDBOX=1 for emit-only）
 - Runner executes Core‑Direct in-proc under HAKO_CORE_DIRECT_INPROC=1.
 - For heavier cases (bundles/alias/require), keep Stage‑B canaries opt‑in in quick profile.
-
diff --git a/tools/selfhost/selfhost_build.sh b/tools/selfhost/selfhost_build.sh
index 7eb561db..1528a366 100644
--- a/tools/selfhost/selfhost_build.sh
+++ b/tools/selfhost/selfhost_build.sh
@@ -24,6 +24,7 @@ fi
 
 IN=""
 JSON_OUT=""
+MIR_OUT=""
 EXE_OUT=""
 DO_RUN=0
 
@@ -32,6 +33,7 @@ while [ $# -gt 0 ]; do
     --in) IN="$2"; shift 2;;
     --json) JSON_OUT="$2"; shift 2;;
     --run) DO_RUN=1; shift;;
+    --mir) MIR_OUT="$2"; shift 2;;
     --exe) EXE_OUT="$2"; shift 2;;
     *) echo "[selfhost] unknown arg: $1" >&2; exit 2;;
   esac
@@ -92,6 +94,12 @@ if [ -n "$JSON_OUT" ]; then
   echo "[selfhost] JSON v0 written: $tmp_json" >&2
 fi
 
+# Optional: emit MIR(JSON) from source (runner compiles .hako directly; Stage‑B JSON is for reference)
+if [ -n "$MIR_OUT" ]; then
+  echo "[selfhost] emitting MIR JSON → $MIR_OUT" >&2
+  "$BIN" --backend mir --emit-mir-json "$MIR_OUT" "$IN" >/dev/null
+fi
+
 # Optional: build native EXE via ny-llvmc harness (fallback path; parses original source)
 if [ -n "$EXE_OUT" ]; then
   # Requirements: ny-llvmc present and harness envs