test: add DOMAIN_NAME to Caddyfile

Containerfile

@@ -1,3 +1,7 @@
+# A hello-world example.
+
+ARG DOMAIN_NAME
+
 FROM stagex/pallet-rust:sx2025.06.1 AS pallet-rust
 FROM stagex/user-eif_build:sx2025.06.1 AS eif_build
 FROM stagex/user-gen_initramfs:sx2025.06.1 AS gen_initramfs
@@ -23,11 +27,21 @@ WORKDIR /build_cpio
 RUN cp /src/target/${TARGET}/release/nit init
 RUN cp /src/target/${TARGET}/release/hello hello
 ENV KBUILD_BUILD_TIMESTAMP=1
+
+ARG DOMAIN_NAME
+COPY <<EOF Caddyfile
+${DOMAIN_NAME} {
+	respond "HTTPS, World!"
+}
+EOF
+
 COPY <<-EOF initramfs.list
 	file /init     init    0755 0 0
 	dir  /run              0755 0 0
 	dir  /tmp              0755 0 0
 	dir  /etc              0755 0 0
+	dir  /etc/caddy        0755 0 0
+	file /etc/caddy/Caddyfile Caddyfile 0755 0 0
 	dir  /bin              0755 0 0
 	dir  /sbin             0755 0 0
 	dir  /proc             0755 0 0

Makefile

@@ -2,9 +2,11 @@
 default: out/nitro.eif
 
 out/nitro.eif: Cargo.lock Cargo.toml Containerfile $(shell git ls-files crates)
+	test ! -z $(DOMAIN_NAME)
 	docker build \
 		--progress=plain \
 		--output type=local,rewrite-timestamp=true,dest=out \
+		--build-arg DOMAIN_NAME=$(DOMAIN_NAME) \
 		-f Containerfile \
 		.