diff --git a/crates/nyash-llvm-compiler/Cargo.toml b/crates/nyash-llvm-compiler/Cargo.toml
index 20c152bf..4efe1197 100644
--- a/crates/nyash-llvm-compiler/Cargo.toml
+++ b/crates/nyash-llvm-compiler/Cargo.toml
@@ -9,3 +9,6 @@ anyhow = "1.0"
 clap = { version = "4.5", features = ["derive"] }
 serde_json = "1.0"
 
+[[bin]]
+name = "ny-llvmc"
+path = "src/main.rs"
diff --git a/src/runner/modes/mir.rs b/src/runner/modes/mir.rs
index b60b36ec..0cf4b2f0 100644
--- a/src/runner/modes/mir.rs
+++ b/src/runner/modes/mir.rs
@@ -64,5 +64,16 @@ impl NyashRunner {
             println!("🚀 MIR Output for {}:", filename);
             println!("{}", printer.print_module(&compile_result.module));
         }
+
+        // Emit MIR JSON if requested and exit
+        if let Some(path) = self.config.emit_mir_json.as_ref() {
+            let p = std::path::Path::new(path);
+            if let Err(e) = crate::runner::mir_json_emit::emit_mir_json_for_harness(&compile_result.module, p) {
+                eprintln!("❌ MIR JSON emit error: {}", e);
+                std::process::exit(1);
+            }
+            println!("MIR JSON written: {}", p.display());
+            std::process::exit(0);
+        }
     }
 }
diff --git a/tools/build_llvm.sh b/tools/build_llvm.sh
index b84bad41..8ee80878 100644
--- a/tools/build_llvm.sh
+++ b/tools/build_llvm.sh
@@ -64,12 +64,16 @@ if [[ "${NYASH_LLVM_SKIP_EMIT:-0}" != "1" ]]; then
     crate)
       # Use crates/nyash-llvm-compiler (ny-llvmc): requires pre-generated MIR JSON path in NYASH_LLVM_MIR_JSON
       if [[ -z "${NYASH_LLVM_MIR_JSON:-}" ]]; then
-        echo "[warn] NYASH_LLVM_COMPILER=crate but NYASH_LLVM_MIR_JSON is not set; falling back to harness" >&2
-        COMPILER_MODE="harness"
-      else
-        echo "    using ny-llvmc (crate) with JSON: $NYASH_LLVM_MIR_JSON" >&2
-        cargo build --release -p nyash-llvm-compiler >/dev/null
-        # Optional schema validation if tool is available
+        # Auto‑emit MIR JSON via nyash CLI flag
+        mkdir -p tmp
+        NYASH_LLVM_MIR_JSON="tmp/nyash_crate_mir.json"
+        echo "    emitting MIR JSON: $NYASH_LLVM_MIR_JSON" >&2
+        ./target/release/nyash --emit-mir-json "$NYASH_LLVM_MIR_JSON" --backend mir "$INPUT" >/dev/null
+      fi
+      echo "    using ny-llvmc (crate) with JSON: $NYASH_LLVM_MIR_JSON" >&2
+      cargo build --release -p nyash-llvm-compiler >/dev/null
+      # Optional schema validation when explicitly requested
+      if [[ "${NYASH_LLVM_VALIDATE_JSON:-0}" == "1" ]]; then
         if [[ -f tools/validate_mir_json.py ]]; then
           if ! python3 -m jsonschema --version >/dev/null 2>&1; then
             echo "[warn] jsonschema not available; skipping schema validation" >&2
@@ -79,8 +83,8 @@ if [[ "${NYASH_LLVM_SKIP_EMIT:-0}" != "1" ]]; then
               echo "error: MIR JSON validation failed" >&2; exit 3; }
           fi
         fi
-        ./target/release/ny-llvmc --in "$NYASH_LLVM_MIR_JSON" --out "$OBJ"
       fi
+      ./target/release/ny-llvmc --in "$NYASH_LLVM_MIR_JSON" --out "$OBJ"
       ;;
   esac
   if [[ "$COMPILER_MODE" == "harness" ]]; then
@@ -101,6 +105,11 @@ if [[ ! -f "$OBJ" ]]; then
   exit 3
 fi
 
+if [[ "${NYASH_LLVM_ONLY_OBJ:-0}" == "1" ]]; then
+  echo "[3/4] Skipping link: object generated at $OBJ (NYASH_LLVM_ONLY_OBJ=1)"
+  exit 0
+fi
+
 echo "[3/4] Building NyRT static runtime ..."
 if [[ "${NYASH_LLVM_SKIP_NYRT_BUILD:-0}" == "1" ]]; then
   echo "    Skipping NyRT build (NYASH_LLVM_SKIP_NYRT_BUILD=1)"