- Fix unsafe JSON construction in a number of locations in the codebase ([#81158](https://github.com/kubernetes/kubernetes/pull/81158), [@zouyee](https://github.com/zouyee))

### Ephemeral Containers Graduate to Stable

  * Plugins

      * Introduces the ability to extend kubectl by adding third-party plugins. Developer preview, please refer to the documentation for instructions about how to use it. ([#37499](https://github.com/kubernetes/kubernetes/pull/37499), [@fabianofranz](https://github.com/fabianofranz))

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* Marked scheduler's scheduling_duration_seconds Summary metric as deprecated ([#86586](https://github.com/kubernetes/kubernetes/pull/86586), [@xiaoanyunfei](https://github.com/xiaoanyunfei))
* Add instructions about how to bring up e2e test cluster ([#85836](https://github.com/kubernetes/kubernetes/pull/85836), [@YangLu1031](https://github.com/YangLu1031))

- Kubeadm: fix a bug when using external CA mode and trying to upgrade to 1.29 using "kubeadm upgrade apply". Show a warning that kubeadm cannot sign the new "super-admin.conf" as the host does not have a CA and show some instructions on how to manually migrate to the separate "admin.conf" and "super-admin.conf" kubeconfig files. ([#124682](https://github.com/kubernetes/kubernetes/pull/124682), [@neolit123](https://github.com/neolit123)) [SIG Cluster Lifecycle]

- The `client.authentication.k8s.io/v1alpha1` ExecCredential has been removed. If you are using a client-go credential plugin that relies on the v1alpha1 API please contact the distributor of your plugin for instructions on how to migrate to the v1 API. ([#108616](https://github.com/kubernetes/kubernetes/pull/108616), [@margocrawf](https://github.com/margocrawf))

### Documentation

- Updated the instructions for deploying the sample app. ([#82785](https://github.com/kubernetes/kubernetes/pull/82785), [@ashish-billore](https://github.com/ashish-billore)) [SIG API Machinery]

### Failing Test

- The helping message of commands which have sub-commands is now clearer and more instructive. It will show the full command instead of `kubectl <command> --help ...`
  

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