build(display): universal binary — compile x86_64 + arm64 and lipo into fat binary

Compiles both arches separately then links with lipo -create.
Prevents silent failure when a binary built on Apple Silicon is deployed
to Intel venue Macs (MacBook Air 2018 fleet).

README.md

@@ -363,6 +363,9 @@ xcode-select --install
 # From the repo root:
 ./scripts/build-display-control.sh
 
+# The script compiles x86_64 and arm64 separately then links a universal binary.
+# Expected output at the end: x86_64 arm64
+
 # Test with a second display connected:
 ./resources/bin/display_control status
 ./resources/bin/display_control extend

scripts/build-display-control.sh

@@ -24,13 +24,26 @@ fi
 
 mkdir -p "$OUT_DIR"
 
-echo "Building display_control..."
-clang -framework Cocoa -framework Carbon \
-    -o "$OUT_BIN" "$SRC"
+TMP_X86="$OUT_DIR/display_control_x86_64"
+TMP_ARM="$OUT_DIR/display_control_arm64"
+
+echo "Building display_control (x86_64)..."
+clang -arch x86_64 -framework Cocoa -framework Carbon \
+    -o "$TMP_X86" "$SRC"
+
+echo "Building display_control (arm64)..."
+clang -arch arm64 -framework Cocoa -framework Carbon \
+    -o "$TMP_ARM" "$SRC"
+
+echo "Linking universal binary..."
+lipo -create -output "$OUT_BIN" "$TMP_X86" "$TMP_ARM"
+rm "$TMP_X86" "$TMP_ARM"
 
 chmod +x "$OUT_BIN"
 
-echo "Built: $OUT_BIN"
+echo ""
+echo "Built universal binary: $OUT_BIN"
+lipo -archs "$OUT_BIN"
 echo ""
 echo "Test it:"
 echo "  $OUT_BIN status"