Fix ownership of HepMC3::GenEvent

[Dr15Jones]

PR description:

The HepMC3Product has never taken ownership of the HepMC3::GenEvent. Callers no longer use release() and the interface has been changed to take a reference to make non-ownership clearer.

PR validation:

Checking memory after the fix shows memory stays constant.

resolves cms-sw/framework-team#1704

[cmsbuild]

cms-bot internal usage

[Dr15Jones]

Please test

[Dr15Jones]

The memory use before and after this fix for a trivial job

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-49522/47011

• There are other open Pull requests which might conflict with changes you have proposed:
  • File SimDataFormats/GeneratorProducts/interface/HepMC3Product.h modified in PR(s): Adding HepMC3 products to EDMProduct #38033

[Dr15Jones]

Please test

[cmsbuild]

A new Pull Request was created by @Dr15Jones for master.

It involves the following packages:

• GeneratorInterface/Core (generators)
• GeneratorInterface/RivetInterface (generators)
• IOMC/EventVertexGenerators (simulation)
• SimDataFormats/GeneratorProducts (generators)

@civanch, @kpedro88, @lviliani, @mdhildreth, @mkirsano, @sensrcn, @theofil can you please review it and eventually sign? Thanks.
@alberto-sanchez, @apsallid, @bsunanda, @denizsun, @fabiocos, @grzanka, @martinamalberti, @missirol, @mkirsano, @mmusich, @rovere, @salimcerci, @youyingli this is something you requested to watch as well.
@ftenchini, @mandrenguyen, @sextonkennedy you are the release manager for this.

cms-bot commands are listed here

[cmsbuild]

+1

Size: This PR adds an extra 36KB to repository
Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-969753/49734/summary.html
COMMIT: fc0b62c
CMSSW: CMSSW_16_0_X_2025-11-28-1100/el8_amd64_gcc13
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week1/cms-sw/cmssw/49522/49734/install.sh to create a dev area with all the needed externals and cmssw changes.

The following merge commits were also included on top of IB + this PR after doing git cms-merge-topic:

• @smuzaffar [FASTSIM] [LLVM21] Apply clang-tidy changes #49495
• @nurfikri89 [JMENano] Fix buggy configuration for Run2 UL JMENanoV15 #49518

You can see more details here:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-969753/49734/git-recent-commits.json
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-969753/49734/git-merge-result

DAS Queries: The DAS query tests failed, see the summary page for details.

Comparison Summary

Summary:

• You potentially added 1 lines to the logs
• ROOTFileChecks: Some differences in event products or their sizes found
• Reco comparison results: 0 differences found in the comparisons
• Reco comparison had 4 failed jobs
• DQMHistoTests: Total files compared: 53
• DQMHistoTests: Total histograms compared: 4269233
• DQMHistoTests: Total failures: 72
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 4269141
• DQMHistoTests: Total skipped: 20
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 52 files compared)
• Checked 227 log files, 198 edm output root files, 53 DQM output files
• TriggerResults: no differences found

[civanch]

+1

[civanch]

@mkirsano, @sensrcn, @theofil , can you, please, review and sign this PR?

[mkirsano]

I am testing this

[mkirsano]

Tests of Pythia8Interface look OK

[mkirsano]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next master IBs (tests are also fine). This pull request will now be reviewed by the release team before it's merged. @mandrenguyen, @ftenchini, @sextonkennedy (and backports should be raised in the release meeting by the corresponding L2)

[mandrenguyen]

+1