Cannot disable autosync using CLI since 3.1.9

[eugenberend]

Checklist:

• I've searched in the docs and FAQ for my answer: https://bit.ly/argocd-faq.
• I've included steps to reproduce the bug.
• I've pasted the output of argocd version.

Describe the bug

Unlike before 3.1.9, argocd app set $APPNAME --sync-policy manual does not disable autosync.

To Reproduce

Create an app

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: hello-world
  namespace: argocd
spec:
  destination:
    namespace: argocd
    server: https://kubernetes.default.svc
  project: sandbox
  source:
    path: hello-world
    repoURL: ssh://git@<some-repo-url>.git
    targetRevision: HEAD
  syncPolicy:
    automated:
      prune: true

If you run argocd app set hello-world --sync-policy manual, inothing changes, the spec remains the same.

Expected behavior

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: hello-world
  namespace: argocd
spec:
  destination:
    namespace: argocd
    server: https://kubernetes.default.svc
  project: sandbox
  source:
    path: hello-world
    repoURL: ssh://git@<some-repo-url>.git
    targetRevision: HEAD
  syncPolicy:
    automated:
      enabled: false # <-- this
      prune: true

Version

➜  ~ argocd version
argocd: v3.1.9+8665140
  BuildDate: 2025-10-17T23:03:44Z
  GitCommit: 8665140f96f6b238a20e578dba7f9aef91ddac51
  GitTreeState: clean
  GoVersion: go1.25.3
  Compiler: gc
  Platform: darwin/arm64
argocd-server: v3.1.9+8665140
  BuildDate: 2025-10-17T21:35:08Z
  GitCommit: 8665140f96f6b238a20e578dba7f9aef91ddac51
  GitTreeState: clean
  GoVersion: go1.24.6
  Compiler: gc
  Platform: linux/amd64
  Kustomize Version: v5.7.0 2025-06-28T07:00:07Z
  Helm Version: v3.18.4+gd80839c
  Kubectl Version: v0.33.1
  Jsonnet Version: v0.21.0