Block Building Algorithm and Flow

1. Sub-block Construction Logic

   1. Each sub-block is built independently:

      • Sources of transactions:

        • Public mempool — sourced in real-time via Reth's local transaction pool (P2P gossip + txpool contents)

        • Private orderflow — received directly via the builder's private RPC endpoint

      • Sorting & Ranking Rules (inside each sub-block):

        1. Nonce ordering per sender — strict ascending nonce enforcement

        2. Effective gas price (priority fee + optional MEV tips / coinbase payment)

        3. Others may affect the ordering

           • Arrival timestamp (for same effective price)

2. Once a sub-block is confirmed:

   • It remains immutable — even if higher-value transactions arrive later in the same slot.

   • No retroactive replacement / reordering is allowed within already-confirmed sub-blocks.

   • This provides strong preconfirmation-like semantics for early-accepted orderflow and prevents last-moment value extraction races from destabilizing earlier commitments.

3. At the end of the slot (or when the slot deadline is reached):

   • The builder concatenates all previously confirmed sub-blocks in sequential order (respecting the exact order in which sub-blocks were sealed).

   • The complete, fully built execution payload is then submitted to one or more relays

   • Proposer then selects & signs header → Relay unblinds → Proposer publishes to network