Summary

Following the decision taken in RFC 103, a node that is catching up (that is, performing BlockSync or StateSync) should not accept incoming transactions until it switches to consensus mode.

See #734.

Proposal

While the node is performing state sync or block sync:

• Disable the RPC endpoints broadcast_txs_* by returning an error.
• The mempool reactor should reject incoming transactions and should not send any transaction that may have in the mempool.

There was a proposal for implementing node phases, but we won't do that here.