build_system: stream build output directly into rootfs

Pipe buildx tar output directly into the mounted rootfs instead of
loading into Docker image store and then exporting. Skips the slow
"exporting layers" step and the intermediate container.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: greatgitsby

build_system.sh

@@ -48,16 +48,6 @@ fi
 export DOCKER_BUILDKIT=1
 docker buildx build -f Dockerfile.agnos --check $DIR
 
-# Start build and create container
-echo "Building agnos-builder docker image"
-BUILD="docker buildx build --load"
-if [ ! -z "$NS" ]; then
-  BUILD="nsc build --load"
-fi
-$BUILD -f Dockerfile.agnos -t agnos-builder $DIR --build-arg UBUNTU_BASE_IMAGE=$UBUNTU_FILE --platform=linux/arm64
-echo "Creating agnos-builder container"
-CONTAINER_ID=$(docker container create --entrypoint /bin/bash agnos-builder:latest)
-
 # Check agnos-meta-builder Dockerfile
 docker buildx build --load -f Dockerfile.builder --check $DIR \
   --build-arg UNAME=$(id -nu) \
@@ -75,7 +65,7 @@ MOUNT_CONTAINER_ID=$(docker run -d --privileged -v $DIR:$DIR agnos-meta-builder)
 
 # Cleanup containers on possible exit
 trap "echo \"Cleaning up containers:\"; \
-docker container rm -f $CONTAINER_ID $MOUNT_CONTAINER_ID" EXIT
+docker container rm -f $MOUNT_CONTAINER_ID" EXIT
 
 # Define functions for docker execution
 exec_as_user() {
@@ -99,12 +89,21 @@ exec_as_root mount $ROOTFS_IMAGE $ROOTFS_DIR
 # Also unmount filesystem (overwrite previous trap)
 trap "exec_as_root umount -l $ROOTFS_DIR &> /dev/null || true; \
 echo \"Cleaning up containers:\"; \
-docker container rm -f $CONTAINER_ID $MOUNT_CONTAINER_ID" EXIT
+docker container rm -f $MOUNT_CONTAINER_ID" EXIT
 
-# Extract image
-echo "Extracting docker image"
-docker container export -o $BUILD_DIR/filesystem.tar $CONTAINER_ID
-exec_as_root tar -xf $BUILD_DIR/filesystem.tar -C $ROOTFS_DIR > /dev/null
+# Build and export filesystem directly as tar, pipe into mounted rootfs
+# This skips --load (slow "exporting layers" into Docker image store) and docker container export
+echo "Building and extracting agnos-builder docker image"
+BUILD="docker buildx build"
+if [ ! -z "$NS" ]; then
+  BUILD="nsc build"
+fi
+$BUILD -f Dockerfile.agnos \
+  --output "type=tar,dest=-" \
+  --provenance=false \
+  --build-arg UBUNTU_BASE_IMAGE=$UBUNTU_FILE \
+  --platform=linux/arm64 \
+  "$DIR" | docker exec -i $MOUNT_CONTAINER_ID tar -xf - -C $ROOTFS_DIR
 
 # Avoid detecting as container
 echo "Removing .dockerenv file"