Add changelog entry

Co-authored-by: Agustin Mista <[email protected]>
Co-authored-by: Alexander Esgen <[email protected]>
Co-authored-by: Georgy Lukyanov <[email protected]>
Co-authored-by: Thomas BAGREL <[email protected]>
Co-authored-by: Nicolas BACQUEY <[email protected]>
Co-authored-by: Nicolas "Niols" Jeannerod <[email protected]>

Author: 6 people

ouroboros-consensus-diffusion/changelog.d/20250919_095435_thomas.bagrel_weighted_chain_selec.md

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+### Breaking
+
+- In module `Ouroboros.Consensus.Node.GSM`, `GSMView` now has a monadic `getCandidateOverSelection :: STM m (selection -> chainSyncState -> CandidateVersusSelection)` instead of the previous pure `candidateOverSelection`. This is due to the fact that chain comparisons now depend on the set of Peras certificates (if Peras is enabled).

ouroboros-consensus/changelog.d/20250917_144846_nicolas.bacquey_weighted_chain_selec.md

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+### Breaking
+
+- Make the `ChainDB` aware of the `PerasCertDB`, and modify the chain selection function accordingly. In practice, it means that the candidate fragment is now selected based on its Peras weight, instead of its length.
+
+  Note that if Peras is disabled (which is the default), there is no observable difference.
+
+- Add module `Ouroboros.Consensus.Peras.SelectView`, which introduces a `WeightedSelectView` to correctly measure the length of a chain fragment.