I think this is correct? But not 100% sure.

No, I don't think so. The change to get_block_scan_start appears to have introduced a bug or exposed buggy behavior elsewhere.

Hmmm But why should it return 7? The only reason it returned 7 before was when it searched for the heaviest affirmation map it showed the lower 7...now it doesn't exist so it searches for the reward cycle minus inv_reward_cycles which in this case means 9 - 1 which is 8. I am not convinced that the test_peer setup is correct now with affirmation maps being gone, but I logically cannot reason out why this would be anything but 8..

This causes net::tests::inv::nakamoto::test_nakamoto_inv_sync_across_epoch_ to infinitely loop as its calls to inv_getpoxinv_begin always returns reward cycle 7 as the start, but it seems to need reward cycle 2. Not yet figured out why. I assume it is a problem with how the test itself is written but struggling to fix

In that test, can you show me what the output of these info! lines are?

        info!(
            "Epoch 2.x state machine: Peer 1: {inv_1_count}, Peer 2: {inv_2_count} (total {num_epoch2_blocks})"
        );
        info!(
            "Nakamoto state machine: Peer 1: {highest_rc_1}, Peer 2: {highest_rc_2} (total {total_rcs})"
        );

Ah nm I see it in the test logs

Can you confirm that InvSync::sync_inventories_epoch2x() is even being called? The fact that inv_1_count and inv_2_count are both zero means that neither peer has done a round of an epoch2x inventory syncs. It's not indicated by the test logs I'm afraid, since it would require debug-logs to figure out.

Yes I confirmed that it is called. See many repeats of the following:

DEBG [1755104776.014222] [stackslib/src/net/inv/epoch2x.rs:2275] [net::tests::inv::nakamoto::test_nakamoto_inv_sync_across_epoch_change] local::60615: Inventory state has 1 block stats tracked on connections {4}
DEBG [1755104776.015142] [stackslib/src/net/inv/epoch2x.rs:2275] [net::tests::inv::nakamoto::test_nakamoto_inv_sync_across_epoch_change] local::60617::pub=127.0.0.1:60617: Inventory state has 1 block stats tracked on connections {3}