Remove the unused ByronToAlonzoEra eon

[Jimbo4350]

Context

Removes the unused ByronToAlonzoEra eon — sister cleanup to the cardano-cli eon removal in IntersectMBO/cardano-cli#1397.

ByronToAlonzoEra (the Cardano.Api.Era.Internal.Eon.ByronToAlonzoEra module) has zero consumers anywhere — cardano-api, cardano-cli, and cardano-node all reference it only via the re-export. It has no case… eliminator either. So this deletes the module, its cardano-api.cabal entry, and the Cardano.Api.Era import/re-export.

This is the safe, standalone part of the broader eon sunset. The three closed-range eons that cli#1397 just freed up — ShelleyToAllegraEra, ShelleyToAlonzoEra, ShelleyToMaryEra — are a breaking removal that must wait until cli#1397 merges and cardano-cli releases against it; they'll follow in a separate PR (at which point this one may be renamed/folded into a broader "remove dead closed-range eons").

How to trust this PR

• git grep ByronToAlonzoEra returns nothing after this change.
• Removal is export-only: no code path used the type, its constructors, or byronToAlonzoEraConstraints.
• Verified with cabal build cardano-api -j4 (clean).

It is an API break (a public export is gone), hence kind: breaking in the changelog fragment.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated
• No version bounds need updating; there are no dependency changes
• Self-reviewed the diff
• Changelog fragment added in .changes/

[Copilot]

Pull request overview

This PR is intended to remove the unused ByronToAlonzoEra closed-range eon from the cardano-api public surface (via Cardano.Api.Era) and from the library build plan.

Changes:

• Deletes the Cardano.Api.Era.Internal.Eon.ByronToAlonzoEra module and removes its Cardano.Api.Era re-export/import.
• Updates cardano-api.cabal to stop listing ByronToAlonzoEra in other-modules.
• Adds a breaking-change changelog fragment in .changes/.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
cardano-api/src/Cardano/Api/Era/Internal/Eon/ShelleyToMaryEra.hs	Deleted module (note: currently conflicts with PR description and leaves dangling references elsewhere).
cardano-api/src/Cardano/Api/Era/Internal/Eon/ShelleyToAlonzoEra.hs	Deleted module (note: currently conflicts with PR description and leaves dangling references elsewhere).
cardano-api/src/Cardano/Api/Era/Internal/Eon/ShelleyToAllegraEra.hs	Deleted module (note: currently conflicts with PR description and leaves dangling references elsewhere).
cardano-api/src/Cardano/Api/Era/Internal/Eon/ByronToAlonzoEra.hs	Deletes the intended unused eon module.
cardano-api/src/Cardano/Api/Era.hs	Removes the ByronToAlonzoEra re-export/import, but still references deleted ShelleyTo* eons.
cardano-api/cardano-api.cabal	Removes ByronToAlonzoEra from other-modules, but still lists deleted ShelleyTo* eons.
.changes/20260720_remove_byrontoalonzoera_eon.yml	Marks the change as breaking, but description no longer matches the effective diff scope.

Comments suppressed due to low confidence (1)

cardano-api/src/Cardano/Api/Era.hs:22

• This module still re-exports ShelleyToAllegraEra, ShelleyToAlonzoEra, and ShelleyToMaryEra, but those modules do not exist under cardano-api/src/Cardano/Api/Era/Internal/Eon/ in this PR (only ShelleyToBabbageEra is present). This will fail to compile with “Could not find module …”. Either restore the removed eon modules, or remove these re-exports and update any dependent API (e.g. the caseShelleyTo* helpers) accordingly.

  , module Cardano.Api.Era.Internal.Eon.ShelleyToAllegraEra
  , module Cardano.Api.Era.Internal.Eon.ShelleyToAlonzoEra
  , module Cardano.Api.Era.Internal.Eon.ShelleyToBabbageEra
  , module Cardano.Api.Era.Internal.Eon.ShelleyToMaryEra