Besu can't backward sync after a restart.

[jflo]

Some kind of race condition seems to be preventing a backward sync session from running with 0 peers. This happened on holesky, after a system restart.

{"@timestamp":"2024-12-28T20:08:03,302","level":"INFO","thread":"vert.x-worker-thread-0","class":"BackwardSyncContext","message":"Starting a new backward sync session","throwable":""}
2024-12-28T20:08:03.312955761Z vert.x-worker-thread-0 WARN found 2 argument placeholders, but provided 3 for pattern `Unable to retrieve block {} from any peer, with {} peers available. Could be a reorged block. Waiting for the next block from t
he consensus client to try again.`
{"@timestamp":"2024-12-28T20:08:03,313","level":"WARN","thread":"vert.x-worker-thread-0","class":"BackwardSyncAlgorithm","message":"Unable to retrieve block 0x41b13c8b0dc2c17c84d9e5c309d865bf91c50aa1bacd570851df46b8728affb9 from any peer, with 0
 peers available. Could be a reorged block. Waiting for the next block from the consensus client to try again.","throwable":""}
{"@timestamp":"2024-12-28T20:08:03,313","level":"INFO","thread":"vert.x-worker-thread-0","class":"BackwardSyncAlgorithm","message":"Current backward sync session is done","throwable":""}
{"@timestamp":"2024-12-28T20:25:50,995","level":"WARN","thread":"vert.x-worker-thread-0","class":"MergeCoordinator","message":"Internal error, backward sync completed but failed to import finalized block 0x1d7358ec1e6f38cad3fe71894de010c7110c03f
a2cbd287de1e2acb01586090e","throwable":""}

Restarting the consensus client (teku) did not help.
Restarting besu did fix it.

[siladu]

BWS requires at least 1 peer to download the block from so I think failure is expected behaviour: the BWS algorithm will keep starting a new session and retrying until there's an EL peer it can download from. We could tidy up the UX for this scenario though.

[macfarla]

suggestion - BWS should wait until peers are available, OR modify the log to say "restarting BWS because 0 peers"

[macfarla]

also should fix this - wrong number of args to log msg
2024-12-28T20:08:03.312955761Z vert.x-worker-thread-0 WARN found 2 argument placeholders, but provided 3 for pattern `Unable to retrieve block {} from any peer, with {} peers available. Could be a reorged block. Waiting for the next block from t