Add failing test for a sync race condition scenario

[jimmygchen]

Issue Addressed

This bug was discovered when the CI kurtosis sync tests got stuck in SyncTransition for a long time:
https://github.com/sigp/lighthouse/actions/runs/17632496975/job/50102884940

I've added a failing test that replicate the exact scenario, and made a fix for it.

NOTE: I haven't done any manual testing yet.

[dapplion]

Nice catch and good test! Some minor comments

[jimmygchen]

I had a look at the failing checkpoint sync tests (optionally triggered jobs), and I don't believe they are related to changes from this PR, i think what's happening is:

• The sepolia checkpoint server used is currently 4 days behind, so it takes longer to sync
• The devnet was under non finality tests, and it was just taking longer to sync.
• Github-hosted runner struggles to sync supernode on peerdas devnet due to capacity, to be resovled in Use unique enclave names for CI Kurtosis tests on self hosted runners #7804 once we have dedicated kurtosis runners.

[jimmygchen]

@dapplion thanks for the review! I've addressed most of your comments.

[pawanjay176]

FYI, running this on devnet 3 i'm getting a stuck chain with 40 peers.
Need to investigate further

[jimmygchen]

Thanks for raising this Pawan. Sorry i haven't managed to get to this today, will look into this tomorrow.

[jimmygchen]

FYI, running this on devnet 3 i'm getting a stuck chain with 40 peers. Need to investigate further

@pawanjay176 im going to remove the clean ups from this PR so we can merge this, because the flaky sync test is really quite annoying 😅

[mergify]

This pull request has merge conflicts. Could you please resolve them @jimmygchen? 🙏