[JENKINS-57618] Implement automated tests for Branch API 2.5.1

JENKINS-57588">JENKINS-57588 fixed branch storm issue introduced in 2.5.0. We need automated tests for this change.

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Originally reported by bitwiseman, imported from: Implement automated tests for Branch API 2.5.1

• assignee: fbelzunc
  
• status: Open
  
• priority: Major
  
• component(s): branch-api-plugin
  
• resolution: Unresolved
  
• votes: 0
  
• watchers: 1
  
• imported: 20251211-141027
  

JENKINS-57588 fixed branch storm issue  introduced in 2.5.0.  We need automated tests for this change. 

Review the branch-api-plugin history around Branch API 2.5.1 and the linked JENKINS-57588 fix first. Identify the existing test entry points for multibranch scanning and define coverage for the first-scan branch-storm regression. Done means automated tests reliably verify that the fixed behavior does not rebuild all multibranch jobs after upgrade.

Written by the indexing model from the issue text.