Prevent infinite recursion in hierarchy ownership updates

[ishitadatta]

Summary

This PR hardens ownership migration against cyclic event/leaderboard-group graphs that can otherwise recurse indefinitely.

What changed

• Added visited-node guards in SailingHierarchyOwnershipUpdater for:
  • events
  • leaderboard groups
  • leaderboards
• Added regression test testCyclicLeagueHierarchyOwnershipChangeStartingAtEventTerminates that builds a cyclic topology (shared leaderboard group across two events with an overall leaderboard) and verifies ownership update completes within a timeout.

Impact

This prevents non-terminating ownership updates and potential stack overflows in production when hierarchy links are cyclic, which is a high-severity reliability issue.

Validation

• Added regression coverage in LeagueEventHierarchyOwnershipChangeTest.
• Local test execution in this environment is blocked because no Java runtime is installed.

[cla-assistant]

All committers have signed the CLA.

[axeluhl]

Good catch, and nice work on the failing test case! :-)

Tracked at https://bugzilla.sapsailing.com/bugzilla/show_bug.cgi?id=6216

For the fix I suggest a few minor modifications. See https://github.com/SAP/sailing-analytics/tree/bug6216. A build is running at https://github.com/SAP/sailing-analytics/actions/runs/22759031743.

[axeluhl]

@ishitadatta can you please sign the CLA so we can include your proposed changes?

[axeluhl]

That test failure of OpenRegattaTest.simpleTest() seems to have been a stray Github Actions infrastructure issue. Locally, the test passes. I've triggered a re-run...

[axeluhl]

Merged branch bug6216 into main with 303cca9.

[axeluhl]

Thanks again, Ishita, for this contribution :-)