Remove the unused ByronToAlonzoEra eon and the closed-range Shelley eons

[Jimbo4350]

Changelog

- description: |
    Remove the unused `ByronToAlonzoEra` eon, and remove the closed-range eons `ShelleyToAllegraEra`, `ShelleyToMaryEra` and `ShelleyToAlonzoEra` together with their eliminators `caseShelleyToAllegraOrMaryEraOnwards`, `caseShelleyToMaryOrAlonzoEraOnwards` and `caseShelleyToAlonzoOrBabbageEraOnwards`. The same era-gating is achieved with `forEraInEon`/`inEonForEra` on `toCardanoEra era`, keyed on the surviving `MaryEraOnwards`/`AlonzoEraOnwards`/`BabbageEraOnwards` eon.
# uncomment types applicable to the change:
  type:
  # - feature        # introduces a new feature
   - breaking       # the API has changed in a breaking way
  # - compatible     # the API has changed but is non-breaking
  # - optimisation   # measurable performance improvements
   - refactoring    # QoL changes
  # - bugfix         # fixes a defect
  # - test           # fixes/modifies tests
  # - maintenance    # not directly related to the code
  # - release        # related to a new release preparation
  # - documentation  # change in code docs, haddocks...
# uncomment at least one main project this PR is associated with
  projects:
   - cardano-api
  # - cardano-api-gen
  # - cardano-rpc
  # - cardano-wasm

Context

Sunsets the dead closed-range eons in cardano-api. Sister cleanup to the cardano-cli eon removal in IntersectMBO/cardano-cli#1397, which removed the last cardano-cli uses of these eons.

Two commits:

1. Remove the unused ByronToAlonzoEra eon

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

2. Replace closed-range eon eliminators with forEraInEon and remove the eons

Rewrites the cardano-api call sites of caseShelleyToAllegraOrMaryEraOnwards, caseShelleyToMaryOrAlonzoEraOnwards and caseShelleyToAlonzoOrBabbageEraOnwards to forEraInEon on the CardanoEra, keyed on the surviving MaryEraOnwards, AlonzoEraOnwards and BabbageEraOnwards eons, then deletes the three eliminators and the now-consumerless ShelleyToAllegraEra, ShelleyToAlonzoEra and ShelleyToMaryEra eons (modules, Cardano.Api.Era re-exports, cardano-api.cabal entries).

ShelleyToBabbageEra and caseShelleyToBabbageOrConwayEraOnwards are retained — they still have consumers.

Behaviour is unchanged. Two sites needed more than a mechanical swap:

• fromLedgerValue (Value/Internal) — forEraInEon's negative branch cannot supply the L.Value ~ Coin evidence that the ShelleyToAllegraEra lower branch provided, so the pre-Mary branch uses lovelaceToValue (L.coin v) (identity on Coin).
• LedgerState.extraEntropy — ppExtraEntropyL needs ProtVerAtMost 6, which forEraInEon cannot supply, so the pre-Babbage eras are matched on ShelleyBasedEra directly.

How to trust this PR

• git grep -E 'ByronToAlonzoEra|ShelleyToAllegraEra|ShelleyToMaryEra|ShelleyToAlonzoEra|caseShelleyToAllegraOrMaryEraOnwards|caseShelleyToMaryOrAlonzoEraOnwards|caseShelleyToAlonzoOrBabbageEraOnwards' returns nothing after this change.
• Every rewrite is a like-for-like translation: case<Lower>Or<Upper>EraOnwards l r sbe becomes forEraInEon (toCardanoEra sbe) <l applied to the lower branch> <r>, with the two exceptions called out above.
• Verified with a clean cabal build cardano-api -j4 (library, gen, cardano-api-test and cardano-api-golden all compile).

Downstream consumers must switch to forEraInEon/inEonForEra on toCardanoEra era, hence type: breaking.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated — none needed; behaviour is unchanged and existing tests cover the rewritten call sites
• No version bounds need updating; there are no dependency changes
• Self-reviewed the diff
• Changelog fragments 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