execution: remove legacy headerdownload, bodydownload and dataflow packages

[taratorio]

Why

headerdownload, bodydownload and dataflow implement the legacy devp2p header/body
download used by the staged-sync Headers/Bodies stages. Post-merge they are dead in
production: blocks arrive from the consensus layer via the engine API / execution module
(PipelineStages), which omits the Headers/Bodies stages entirely. The path was already
disabled — sentryMcDisableBlockDownload = true made MultiClient.Hd/Bd empty stubs, the
eth/66 download handlers early-returned, and StageLoop's only caller was the dead
pre-merge-PoW branch in Ethereum.Start().

What

• Delete the three packages (~4.7k lines).
• Headers/Bodies stage forward funcs become no-ops; their unwinds are kept but
  decoupled from headerdownload.
• Remove StageLoop + StageLoopIteration + ProcessFrozenBlocks and the legacy
  non-PoS / non-Bor branch in Ethereum.Start().
• Strip Hd/Bd from sentry_multi_client: the four download message handlers (now a
  single no-op dispatch case), SendHeaderRequest/SendBodyRequest/Penalize, and the
  dead broadcast.go (BroadcastNewBlock/PropagateNewBlockHashes).
• Remove the dead params/plumbing this exposed: Sync.posTransition, the execute stage's
  unused hd interface + the dead POSSync()→ReportBadHeaderPoS branches,
  disableBlockDownload, blockBufferSize/DefaultBlockBufferSize, maxBlockBroadcastPeers.
• Rework the MockSentry test fixture to drop the vestigial downloader — tests already
  insert blocks via the PoS engine-API path (InsertChain → UpdateForkChoice).

Behavior note: a bare pre-merge PoW chain (not PoS, not Bor) no longer starts a sync
loop — consistent with StageLoop being unused in production. PoS and Polygon are unaffected.

Verification

go build ./..., make erigon integration, and make lint are clean; targeted tests pass
(stagedsync, sentry_multi_client, execmoduletester, execution/tests, polygon/bor).
Full make test-all (on ramdisk) is running.

[Copilot]

Pull request overview

This PR removes Erigon’s legacy devp2p-based header/body download pipeline (headerdownload, bodydownload, dataflow) and the associated staged-sync loop plumbing that was already effectively dead in production post-merge. The remaining staged-sync “Headers/Bodies” stages are turned into forward no-ops (unwinds retained), and the sentry multi-client is simplified to drop the internal downloaders and related message handling/broadcasting.

Changes:

• Delete legacy header/body downloader and dataflow packages; remove StageLoop-based syncing and related backend plumbing.
• Simplify sentry_multi_client (drop Hd/Bd, disable download handlers, remove broadcast helpers, reduce constructor deps).
• Adjust staged-sync stage configs/APIs (headers/bodies forward no-ops; remove downloader hooks from senders/execute) and update affected tests/integration tooling.

Reviewed changes

Copilot reviewed 33 out of 33 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
polygon/bor/bor_test.go	Removes now-deleted WithBlockBufferSize option usage in Bor tests.
p2p/sentry/sentry_multi_client/sentry_multi_client.go	Drops embedded Hd/Bd downloaders and turns eth/66 download inbound messages into no-ops.
p2p/sentry/sentry_multi_client/sentry_api.go	Removes legacy request/penalty APIs tied to header/body downloading.
p2p/sentry/sentry_multi_client/broadcast.go	Deletes legacy devp2p new-block/new-hash broadcast helpers.
node/eth/backend.go	Removes legacy StageLoop startup/shutdown and sentry multi-client downloader plumbing; PoW-only branch no longer starts sync loop.
node/components/sentry/provider.go	Simplifies MultiClientDeps and BuildMultiClient call (removes sync cfg/buffer/broadcast/download flags).
execution/tests/blockchain_test.go	Removes now-deleted WithBlockBufferSize option usage in execution tests.
execution/stagedsync/sync.go	Removes posTransition gating from break-after-stage logic.
execution/stagedsync/stageloop/stageloop.go	Removes StageLoop/ProcessFrozenBlocks/StageLoopIteration and updates stage construction to no longer depend on Hd/Bd.
execution/stagedsync/stage_witness.go	Updates Execute stage cfg construction for witness rewind (but currently has a signature/order mismatch—see comment).
execution/stagedsync/stage_senders.go	Removes hd-based PoS bad-header reporting hooks from Senders stage.
execution/stagedsync/stage_senders_test.go	Updates senders stage cfg call signature.
execution/stagedsync/stage_headers.go	Replaces headers stage cfg with a minimal cfg; keeps unwind logic but removes downloader interactions.
execution/stagedsync/stage_execute.go	Removes header-downloader interface hook from execute stage configuration.
execution/stagedsync/stage_bodies.go	Removes bodies forward download logic; keeps unwind via block writer canonical markers.
execution/stagedsync/exec3.go	Removes bad-header reporting hook from wrong-trie-root path; adjusts helper signature accordingly.
execution/stagedsync/exec3_serial.go	Removes PoS bad-header reporting hook on serial execution invalid block.
execution/stagedsync/exec3_parallel.go	Removes PoS bad-header reporting hook on parallel execution invalid block; updates helper signature usage.
execution/stagedsync/default_stages.go	Makes Headers/Bodies forward functions no-ops while retaining unwind hooks.
execution/stagedsync/dataflow/states.go	Deletes legacy download state tracking utility.
execution/stagedsync/headerdownload/header_data_struct.go	Deletes legacy header download implementation.
execution/stagedsync/headerdownload/header_algos.go	Deletes legacy header download implementation.
execution/stagedsync/headerdownload/header_algo_test.go	Deletes legacy header download tests.
execution/stagedsync/bodydownload/prefetched_blocks.go	Deletes legacy body prefetch cache used by downloader.
execution/stagedsync/bodydownload/body_test.go	Deletes legacy body downloader tests.
execution/stagedsync/bodydownload/body_data_struct.go	Deletes legacy body download implementation.
execution/stagedsync/bodydownload/body_algos.go	Deletes legacy body download implementation.
execution/stagedsync/bodydownload/block_propagator.go	Deletes legacy block propagator type used by downloader.
execution/execmodule/execmoduletester/from0_genesis_internal_test.go	Removes passing Hd into execute cfg builder.
execution/execmodule/execmoduletester/exec_module_tester.go	Removes WithBlockBufferSize, drops internal downloader wiring from mock sentry setup and stage construction.
db/snapshotsync/freezeblocks/dump_test.go	Removes now-deleted WithBlockBufferSize option usage.
cmd/integration/commands/state_stages.go	Updates execute stage cfg calls for signature change (removes hd arg).
cmd/integration/commands/stages.go	Updates bodies/senders/exec integration commands for new stage cfg signatures and NewDefaultStages signature change.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.