[JENKINS-49341] Pipeline retry clause : expose the retry number

When inside the `retry{}` clause, it may be useful to know which attempt number this is (e.g. to `archiveArtifacts` the debug logs under a uniquely named archive). Expose the retry number as a groovy and/or environment variable.

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Originally reported by jimklimov, imported from: Pipeline retry clause : expose the retry number

• status: In Progress
  
• priority: Minor
  
• component(s): workflow-basic-steps-plugin
  
• resolution: Unresolved
  
• votes: 9
  
• watchers: 11
  
• imported: 20251215-220547
  

Raw content of original issue

When inside the `retry{}` clause, it may be useful to know which attempt number this is (e.g. to `archiveArtifacts` the debug logs under a uniquely named archive). Expose the retry number as a groovy and/or environment variable.