wip: fast-forward buffered streaming + async task cancellation safety + lock free state

[0xOsiris]

Note

Medium Risk
Reworks the flashblock execution pipeline to use per-epoch async processors and broadcast-driven notifications, which can change ordering/cancellation semantics and impact pending-block/payload propagation under load.

Overview
Refactors flashblock execution from a single, coordinator-owned state machine into an epoch-scoped processing model: run_flashblock_processor now detects payload_id boundaries, spawns a PendingPayloadProcessor per epoch, and cancels the previous epoch by dropping its broadcast sender.

Adds a new processor module that centralizes pending-block mutations and payload event broadcasting via PendingBlockNotification, and updates the coordinator’s local-payload publish path to notify this processor after P2P broadcast.

Updates the builder APIs (BlockBuilderExt) and executors to support new plumbing (new trait hooks, committed-state construction helper), and adjusts benchmarks/dependencies (adds tokio-stream and op-alloy-rpc-types-engine) to drive the new stream-based processor path.

^{Written by Cursor Bugbot for commit dad6f1f. Configure here.}

[github-actions]

Benchmark Results

Compared on the same runner in the same workflow run.

group                                                                        base
-----                                                                        ----
launch_flashblock_sequence_eth_transfers/stream/4fb_x_125tx                  1.00     30.6±0.42ms        ? ?/sec
launch_flashblock_sequence_eth_transfers/stream/4fb_x_250tx                  1.00     58.1±0.32ms        ? ?/sec
launch_flashblock_sequence_eth_transfers/stream/4fb_x_50tx                   1.00     12.9±0.65ms        ? ?/sec
launch_flashblock_sequence_eth_transfers_with_bal/stream/4fb_x_125tx         1.00     37.3±0.68ms        ? ?/sec
launch_flashblock_sequence_eth_transfers_with_bal/stream/4fb_x_250tx         1.00     72.1±0.94ms        ? ?/sec
launch_flashblock_sequence_eth_transfers_with_bal/stream/4fb_x_50tx          1.00     16.3±0.49ms        ? ?/sec
launch_flashblock_sequence_fib/stream/4fb_x_125tx                            1.00     28.2±0.24ms        ? ?/sec
launch_flashblock_sequence_fib/stream/4fb_x_250tx                            1.00     53.9±0.73ms        ? ?/sec
launch_flashblock_sequence_fib/stream/4fb_x_50tx                             1.00     12.5±0.35ms        ? ?/sec
launch_flashblock_sequence_fib_with_bal/stream/4fb_x_125tx                   1.00     34.9±0.24ms        ? ?/sec
launch_flashblock_sequence_fib_with_bal/stream/4fb_x_250tx                   1.00     67.0±0.96ms        ? ?/sec
launch_flashblock_sequence_fib_with_bal/stream/4fb_x_50tx                    1.00     15.4±0.19ms        ? ?/sec
launch_flashblock_sequence_world_id_like_bn254/stream/4fb_x_10tx             1.00    137.3±0.34ms        ? ?/sec
launch_flashblock_sequence_world_id_like_bn254/stream/4fb_x_12tx             1.00    164.3±0.47ms        ? ?/sec
launch_flashblock_sequence_world_id_like_bn254/stream/4fb_x_5tx              1.00     69.0±0.17ms        ? ?/sec
launch_flashblock_sequence_world_id_like_bn254_with_bal/stream/4fb_x_10tx    1.00    141.1±1.86ms        ? ?/sec
launch_flashblock_sequence_world_id_like_bn254_with_bal/stream/4fb_x_12tx    1.00    167.9±0.85ms        ? ?/sec
launch_flashblock_sequence_world_id_like_bn254_with_bal/stream/4fb_x_5tx     1.00     72.1±0.87ms        ? ?/sec
process_flashblock_eth_transfers/txs/1000                                    1.00     48.1±0.31ms        ? ?/sec
process_flashblock_eth_transfers/txs/50                                      1.00      3.0±0.04ms        ? ?/sec
process_flashblock_eth_transfers/txs/500                                     1.00     25.3±2.79ms        ? ?/sec
process_flashblock_eth_transfers_with_bal/txs/1000                           1.00     78.9±1.47ms        ? ?/sec
process_flashblock_eth_transfers_with_bal/txs/50                             1.00      3.7±0.06ms        ? ?/sec
process_flashblock_eth_transfers_with_bal/txs/500                            1.00     33.0±1.02ms        ? ?/sec
process_flashblock_fib/txs/1000                                              1.00     47.0±0.17ms        ? ?/sec
process_flashblock_fib/txs/50                                                1.00      2.5±0.02ms        ? ?/sec
process_flashblock_fib/txs/500                                               1.00     23.6±0.11ms        ? ?/sec
process_flashblock_fib_with_bal/txs/1000                                     1.00     66.4±1.09ms        ? ?/sec
process_flashblock_fib_with_bal/txs/50                                       1.00      3.6±0.06ms        ? ?/sec
process_flashblock_fib_with_bal/txs/500                                      1.00     31.8±1.52ms        ? ?/sec
process_flashblock_world_id_like_bn254/txs/10                                1.00     34.3±0.55ms        ? ?/sec
process_flashblock_world_id_like_bn254/txs/25                                1.00     84.9±0.31ms        ? ?/sec
process_flashblock_world_id_like_bn254/txs/50                                1.00    169.4±0.31ms        ? ?/sec
process_flashblock_world_id_like_bn254_with_bal/txs/10                       1.00     35.1±0.39ms        ? ?/sec
process_flashblock_world_id_like_bn254_with_bal/txs/25                       1.00     86.4±0.23ms        ? ?/sec
process_flashblock_world_id_like_bn254_with_bal/txs/50                       1.00    172.1±0.83ms        ? ?/sec

Threshold: 10% regression triggers failure