examples/jamstack: implemented image_ref

Signed-off-by: Sam Alba <sam.alba@gmail.com>

examples/jamstack/ecr_image.cue

@@ -25,7 +25,10 @@ import (
 		target: pushTarget
 	}
 
-	push: #up: [
+	ref: {
+		string
+
+		#up: [
 			// Build the docker image
 			op.#DockerBuild & {
 				context: source
@@ -38,8 +41,10 @@ import (
 			op.#PushContainer & {
 				ref: pushTarget
 			},
+			op.#Export & {
+				source: "/dagger/image_ref"
+				format: "string"
+			},
 		]
-
-	// FIXME: ref does not include the sha256: https://github.com/dagger/dagger/issues/303
-	ref: pushTarget
+	}
 }