Guarantee spec compliance of eth_subscribe's newHeads

[manuelmauro]

⚠️ Breaking Changes ⚠️

The previous implementation was not compliant with the Ethereum specs, thus the new (compliant) behavior might be considered a breaking change with regard to previous assumptions.

In particular, while the current implementation in case of a reorg just returns the new head with a parent hash that was never mentioned within the subscription, the new behavior according to the specs is as follows:

"When a chain reorganization occurs, this subscription will emit an event containing all new headers (blocks) for the new chain. This means that you may see multiple headers emitted with the same height (block number), and when this happens the later (highest) block number should be taken as the correct one after a reorganization."

What does it do?

Guarantees spec compliance of eth_subscribe's newHeads.

More information here:https://github.com/ethereum/go-ethereum/wiki/RPC-PUB-SUB/7a0c1704737ece636aabda1d08d43f96dd1a619f#newheads

Relevant PRs

• Extend EthereumBlockNotification with reorg info to allow compliance with Ethereum specs polkadot-evm/frontier#1787

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[github-actions]

WASM runtime size check:

Compared to target branch

Moonbase runtime: 2108 KB (no changes) ✅

Moonbeam runtime: 2232 KB (no changes) ✅

Moonriver runtime: 2232 KB (no changes) ✅

Compared to latest release (runtime-4100)

Moonbase runtime: 2108 KB (+172 KB compared to latest release) ⚠️

Moonbeam runtime: 2232 KB (+200 KB compared to latest release) ⚠️

Moonriver runtime: 2232 KB (+200 KB compared to latest release) ⚠️

[github-actions]

Coverage Report

@@                                      Coverage Diff                                      @@
##           master   manuel/test-for-spec-compliance-of-eth-subscribe-new-heads     +/-   ##
=============================================================================================
  Coverage   76.65%                                                       76.65%   0.00%     
  Files         389                                                          389             
  Lines       76440                                                        76440             
=============================================================================================
  Hits        58595                                                        58595             
  Misses      17845                                                        17845             

Files Changed	Coverage

Coverage generated Thu Jan 8 10:50:06 UTC 2026