Fix temporary offline state of computer is lost on config submit

[mawinter69]

Fixes #26146

I suspect that #9855 is the cause for the issue.
I could reproduce the issue in version 2.492.3 so it exists since a while.

Root cause is that the config is based on the a Computer Object while the persistence is based on a Node object. Upon saving the configuration of a computer a new Node object is created based from the form fields but as the cause is not part of the form it is not persisted. Before #9855 the temporaryOfflineCcause was kept in the computer object directly, so a change in config didn't lead to a loss as the Computer object continues to live (might have caused a loss at restart though).
The fix is to set the cause after the new Node object is created before re-establishing the connection between computer and new Node object.

Testing done

• Create a computer
• set it to temporary offline
• configure the computer (no change necessary) and save
• computer is still set to temporary offline
• restarted Jenkins and verified computer is still offline

Added a unit test that fails without the fix and succeeds with the fix

Screenshots (UI changes only)

Before

After

Proposed changelog entries

• Fix temporary offline state of computer is lost on config submit

Proposed changelog category

/label bug,regression-fix

Proposed upgrade guidelines

N/A

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Desired reviewers

@mention

Before the changes are marked as ready-for-merge:

Maintainer checklist

• There are at least two (2) approvals for the pull request and no outstanding requests for change.
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[MarkEWaite]

I've updated the label on the bug report to add lts-candidate and removed the into-lts label from this pull request. We use into-lts for pull requests that are targeting a backport branch (like stable-2.541).

[Copilot]

Pull request overview

This PR fixes a bug where a computer's temporary offline state was lost when its configuration was submitted. The root cause was that configuration is based on a Computer object while persistence is based on a Node object - when saving configuration, a new Node object is created from form fields, but the temporary offline cause is not part of the form and was therefore lost.

Changes:

• Preserve temporary offline cause during node reconfiguration by saving it before reconfiguration and restoring it to the new node
• Add unit test to verify temporary offline cause persists through configuration roundtrip

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
core/src/main/java/hudson/model/Computer.java	Added code to preserve and restore the temporary offline cause when reconfiguring a node
test/src/test/java/hudson/model/ComputerTest.java	Added test case to verify temporary offline cause is preserved through configuration roundtrip

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[MarkEWaite]

This PR is now ready for merge. We will merge it after approximately 24 hours if there is no negative feedback.

/label ready-for-merge

[timja]

I assume it also fixes jenkinsci/configuration-as-code-plugin#2682 ?

[mawinter69]

likely