diff --git a/packages/physics-rs/build-gdext.sh b/packages/physics-rs/build-gdext.sh
index f4f8ea85..51f92b24 100755
--- a/packages/physics-rs/build-gdext.sh
+++ b/packages/physics-rs/build-gdext.sh
@@ -1,4 +1,31 @@
 #!/usr/bin/env bash
 set -euo pipefail
+
 TARGET=${1:-x86_64-unknown-linux-gnu}
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+ADDON_DIR="$SCRIPT_DIR/../../engine/addons/magic_civ_physics"
+
 cargo build --release --features gdext --target "$TARGET"
+
+mkdir -p "$ADDON_DIR"
+
+case "$TARGET" in
+  x86_64-unknown-linux-gnu)
+    cp "$SCRIPT_DIR/target/$TARGET/release/libmagic_civ_physics.so" \
+       "$ADDON_DIR/libmagic_civ_physics.x86_64.so"
+    echo "Copied → engine/addons/magic_civ_physics/libmagic_civ_physics.x86_64.so"
+    ;;
+  x86_64-pc-windows-gnu|x86_64-pc-windows-msvc)
+    cp "$SCRIPT_DIR/target/$TARGET/release/magic_civ_physics.dll" \
+       "$ADDON_DIR/magic_civ_physics.x86_64.dll"
+    echo "Copied → engine/addons/magic_civ_physics/magic_civ_physics.x86_64.dll"
+    ;;
+  aarch64-apple-darwin|x86_64-apple-darwin)
+    cp "$SCRIPT_DIR/target/$TARGET/release/libmagic_civ_physics.dylib" \
+       "$ADDON_DIR/libmagic_civ_physics.dylib"
+    echo "Copied → engine/addons/magic_civ_physics/libmagic_civ_physics.dylib"
+    ;;
+  *)
+    echo "Unknown target $TARGET — skipping copy. Place .so/.dll manually in engine/addons/magic_civ_physics/"
+    ;;
+esac