`docker extension validate` failure

[doberkofler]

Describe the bug
After generating the sample extension, docker extension validate reports an error ERRO Use "--platform=linux/amd64,linux/arm64" when pushing your image to DockerHub that does not seem to be correct.

Add the steps to reproduce

1. docker extension init awesome-extension
2. change TAG?=1.0.0 in Makefile
3. make push-extension
4. docker extension validate doberkofler/awesome-extension

Describe the expected behavior
Given that docker buildx imagetools inspect doberkofler/awesome-extension:1.0.0 reports the two platforms, why does validate report an error?

Name:      docker.io/doberkofler/awesome-extension:1.0.0
MediaType: application/vnd.oci.image.index.v1+json
Digest:    sha256:9e946aac7b2638347991eb23a6bb87292a7acadc85b2461bd2ecf71f3ad303a3
           
Manifests: 
  Name:        docker.io/doberkofler/awesome-extension:1.0.0@sha256:d2699376344f37b5fe5dff18d838d9a08a2a062a9ce5cea09fedde7fa2c6f165
  MediaType:   application/vnd.oci.image.manifest.v1+json
  Platform:    linux/amd64
               
  Name:        docker.io/doberkofler/awesome-extension:1.0.0@sha256:7c1c04c35593183c429e2260386b5945028c84a608345c3322d5e8be29dc647d
  MediaType:   application/vnd.oci.image.manifest.v1+json
  Platform:    linux/arm64
               
  Name:        docker.io/doberkofler/awesome-extension:1.0.0@sha256:935de2c9a0a412851af5c03029e4faef71e15d6b5edf503a00230b19fb42d1b4
  MediaType:   application/vnd.oci.image.manifest.v1+json
  Platform:    unknown/unknown
  Annotations: 
    vnd.docker.reference.digest: sha256:d2699376344f37b5fe5dff18d838d9a08a2a062a9ce5cea09fedde7fa2c6f165
    vnd.docker.reference.type:   attestation-manifest
               
  Name:        docker.io/doberkofler/awesome-extension:1.0.0@sha256:0a9ac38c5ba4fd7c4f3c381ab52f36ed54b9a33c35f66f15a3bd57495f617440
  MediaType:   application/vnd.oci.image.manifest.v1+json
  Platform:    unknown/unknown
  Annotations: 
    vnd.docker.reference.digest: sha256:7c1c04c35593183c429e2260386b5945028c84a608345c3322d5e8be29dc647d
    vnd.docker.reference.type:   attestation-manifest

Output of docker extension version:

Client Version: v0.2.31
Server API Version: 0.4.2

Output of docker version:

Client:
 Version:           28.5.1
 API version:       1.51
 Go version:        go1.24.8
 Git commit:        e180ab8
 Built:             Wed Oct  8 12:16:17 2025
 OS/Arch:           darwin/amd64
 Context:           desktop-linux

Server: Docker Desktop 4.50.0 (209931)
 Engine:
  Version:          28.5.1
  API version:      1.51 (minimum version 1.24)
  Go version:       go1.24.8
  Git commit:       f8215cc
  Built:            Wed Oct  8 12:17:24 2025
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.7.27
  GitCommit:        05044ec0a9a75232cad458027ca83437aae3f4da
 runc:
  Version:          1.2.5
  GitCommit:        v1.2.5-0-g59923ef
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0