test: add resumable isolated test harness

scripts/test-integration

@@ -1,6 +1,13 @@
 #!/bin/sh
 set -eu
 
-echo "integration harness is not implemented yet; use scripts/test-unit for the current Phase 0/1 scope" >&2
-exit 2
+repo_root=$(CDPATH= cd -- "$(dirname -- "$0")/.." && pwd)
+toolchain_image=$(docker compose -f "$repo_root/deploy/compose.yaml" images -q toolchain 2>/dev/null || true)
+if [ -z "$toolchain_image" ]; then
+  toolchain_image=$(docker image inspect rvbox-dev-toolchain --format '{{.Id}}' 2>/dev/null || true)
+fi
 
+cd "$repo_root"
+exec docker compose -f deploy/compose.yaml run --rm \
+  -e "RVBOX_TOOLCHAIN_IMAGE=$toolchain_image" \
+  toolchain go run ./test/harness integration "$@"