From c0b91de78ec9f9462af175a781a289fae474a557 Mon Sep 17 00:00:00 2001
From: Aniket Deshpande <git@aniketd.net>
Date: Wed, 13 May 2026 20:20:52 +0530
Subject: [PATCH 01/13] Add decodeSparseKeyed; use for BabbageTxOut PV12+.

---
 eras/babbage/impl/cardano-ledger-babbage.cabal |  4 ++--
 .../impl/src/Cardano/Ledger/Babbage/TxOut.hs   | 18 +++++++++---------
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/eras/babbage/impl/cardano-ledger-babbage.cabal b/eras/babbage/impl/cardano-ledger-babbage.cabal
index fa720e8b829..ae7f66a1614 100644
--- a/eras/babbage/impl/cardano-ledger-babbage.cabal
+++ b/eras/babbage/impl/cardano-ledger-babbage.cabal
@@ -92,7 +92,7 @@ library
     cardano-data >=1.2,
     cardano-ledger-allegra ^>=1.10,
     cardano-ledger-alonzo ^>=1.16,
-    cardano-ledger-binary >=1.6,
+    cardano-ledger-binary >=1.9,
     cardano-ledger-core:{cardano-ledger-core, internal} >=1.20,
     cardano-ledger-mary ^>=1.11,
     cardano-ledger-shelley ^>=1.19,
@@ -146,7 +146,7 @@ executable generate-cddl
 
   build-depends:
     base,
-    cardano-ledger-binary:testlib >=1.5,
+    cardano-ledger-binary:testlib >=1.9,
     cddl,
 
 library testlib
diff --git a/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs b/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs
index f910b8f9f9d..4e41eb5fd5c 100644
--- a/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs
+++ b/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs
@@ -621,37 +621,37 @@ decodeTxOut decAddr = do
     initial :: DecodingTxOut era
     initial = DecodingTxOut SNothing mempty NoDatum SNothing
     decoderForKey :: DecodingTxOut era -> Word -> Maybe (Decoder s (DecodingTxOut era))
-    decoderForKey txo = \case
+    decoderForKey txOut = \case
       0 -> Just $ do
         !x <- decAddr
-        pure txo {decodingTxOutAddr = SJust x}
+        pure txOut {decodingTxOutAddr = SJust x}
       1 -> Just $ do
         !x <- decCBOR
-        pure txo {decodingTxOutVal = x}
+        pure txOut {decodingTxOutVal = x}
       2 -> Just $ do
         !x <- decCBOR
-        pure txo {decodingTxOutDatum = x}
+        pure txOut {decodingTxOutDatum = x}
       3 -> Just $ do
         !x <- decodeCIC "Script"
-        pure txo {decodingTxOutScript = SJust x}
+        pure txOut {decodingTxOutScript = SJust x}
       _ -> Nothing
     {-# INLINE decoderForKey #-}
     bodyFields :: (Word -> Field (DecodingTxOut era))
     bodyFields 0 =
       field
-        (\x txo -> txo {decodingTxOutAddr = SJust x})
+        (\x txOut -> txOut {decodingTxOutAddr = SJust x})
         (D decAddr)
     bodyFields 1 =
       field
-        (\x txo -> txo {decodingTxOutVal = x})
+        (\x txOut -> txOut {decodingTxOutVal = x})
         From
     bodyFields 2 =
       field
-        (\x txo -> txo {decodingTxOutDatum = x})
+        (\x txOut -> txOut {decodingTxOutDatum = x})
         (D decCBOR)
     bodyFields 3 =
       ofield
-        (\x txo -> txo {decodingTxOutScript = x})
+        (\x txOut -> txOut {decodingTxOutScript = x})
         (D $ decodeCIC "Script")
     bodyFields n = invalidField n
     {-# INLINE bodyFields #-}

From 5ca36f379a0318a836d91cefea5fee54c52771db Mon Sep 17 00:00:00 2001
From: Aniket Deshpande <git@aniketd.net>
Date: Mon, 18 May 2026 19:42:39 +0530
Subject: [PATCH 02/13] Use decodeSparseKeyed for AlonzoTxAuxData PV12+.

---
 .../src/Cardano/Ledger/Alonzo/TxAuxData.hs    | 49 ++++++++++++++++++-
 1 file changed, 48 insertions(+), 1 deletion(-)

diff --git a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
index f47cb58c241..4d1610b03dc 100644
--- a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
+++ b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE DerivingVia #-}
@@ -67,6 +68,8 @@ import Cardano.Ledger.Binary (
   EncCBOR (..),
   ToCBOR,
   TokenType (..),
+  assertTag,
+  decodeSparseKeyed,
   decodeStrictSeq,
   ifDecoderVersionAtLeast,
   natVersion,
@@ -202,7 +205,18 @@ instance
     decodeTxAuxDataByTokenType @(Annotator (AlonzoTxAuxDataRaw era))
       decodeShelley
       (ifDecoderVersionAtLeast (natVersion @12) decodeDijkstra decodeAllegra)
-      decodeAlonzo
+      ( ifDecoderVersionAtLeast
+          (natVersion @12)
+          ( do
+              assertTag 259
+              decodeSparseKeyed
+                "AlonzoTxAuxData"
+                []
+                (pure emptyAlonzoTxAuxDataRaw)
+                decoderForKey
+          )
+          decodeAlonzo
+      )
     where
       decodeShelley =
         decode
@@ -229,6 +243,39 @@ instance
           TagD 259 $
             SparseKeyed "AlonzoTxAuxData" (pure emptyAlonzoTxAuxDataRaw) auxDataField []
 
+      decoderForKey ::
+        Annotator (AlonzoTxAuxDataRaw era) ->
+        Word ->
+        Maybe (Decoder s (Annotator (AlonzoTxAuxDataRaw era)))
+      decoderForKey acc = \case
+        0 -> Just $ do
+          !x <- decCBOR
+          pure $ (\ad -> ad {atadrMetadata = x}) <$> acc
+        1 -> Just $ do
+          !x <- sequence <$> decodeStrictSeq decCBOR
+          pure $
+            (\scripts ad -> ad {atadrNativeScripts = atadrNativeScripts ad <> scripts})
+              <$> x
+              <*> acc
+        2 -> Just $ do
+          guardPlutus PlutusV1
+          !x <- decCBOR
+          pure $ addPlutusScripts PlutusV1 x <$> acc
+        3 -> Just $ do
+          guardPlutus PlutusV2
+          !x <- decCBOR
+          pure $ addPlutusScripts PlutusV2 x <$> acc
+        4 -> Just $ do
+          guardPlutus PlutusV3
+          !x <- decCBOR
+          pure $ addPlutusScripts PlutusV3 x <$> acc
+        5 -> Just $ do
+          guardPlutus PlutusV4
+          !x <- decCBOR
+          pure $ addPlutusScripts PlutusV4 x <$> acc
+        _ -> Nothing
+      {-# INLINE decoderForKey #-}
+
       auxDataField :: Word -> Field (Annotator (AlonzoTxAuxDataRaw era))
       auxDataField 0 = fieldA (\x ad -> ad {atadrMetadata = x}) From
       auxDataField 1 =

From 6438b666d59c941d28045327cc7e50eb1297c550 Mon Sep 17 00:00:00 2001
From: Aniket Deshpande <git@aniketd.net>
Date: Tue, 19 May 2026 20:00:29 +0530
Subject: [PATCH 03/13] Use decodeSparseKeyed for PParamsUpdate PV12+

---
 .../src/Cardano/Ledger/Core/PParams.hs        | 22 ++++++++++++++-----
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/libs/cardano-ledger-core/src/Cardano/Ledger/Core/PParams.hs b/libs/cardano-ledger-core/src/Cardano/Ledger/Core/PParams.hs
index 9a9a413e4c8..9017ff0ee26 100644
--- a/libs/cardano-ledger-core/src/Cardano/Ledger/Core/PParams.hs
+++ b/libs/cardano-ledger-core/src/Cardano/Ledger/Core/PParams.hs
@@ -115,9 +115,12 @@ import Cardano.Ledger.Binary (
   FromCBOR (..),
   ToCBOR (..),
   decodeRecordNamed,
+  decodeSparseKeyed,
   encodeListLen,
   encodeMapLen,
   encodeWord,
+  ifDecoderVersionAtLeast,
+  natVersion,
  )
 import Cardano.Ledger.Binary.Coders (Decode (..), Field (..), decode, field, invalidField)
 import Cardano.Ledger.Coin (
@@ -252,13 +255,20 @@ instance EraPParams era => EncCBOR (PParamsUpdate era) where
 
 instance EraPParams era => DecCBOR (PParamsUpdate era) where
   decCBOR =
-    decode $
-      SparseKeyed
-        (show . typeRep $ Proxy @(PParamsUpdate era))
-        emptyPParamsUpdate
-        updateField
-        []
+    ifDecoderVersionAtLeast
+      (natVersion @12)
+      (decodeSparseKeyed name [] emptyPParamsUpdate decoderForKey)
+      (decode $ SparseKeyed name emptyPParamsUpdate updateField [])
     where
+      name = show . typeRep $ Proxy @(PParamsUpdate era)
+      decoderForKey ::
+        PParamsUpdate era ->
+        Word ->
+        Maybe (Decoder s (PParamsUpdate era))
+      decoderForKey acc k =
+        case IntMap.lookup (fromIntegral k) updateFieldMap of
+          Just (Field setter dec) -> Just $ (`setter` acc) <$> dec
+          Nothing -> Nothing
       updateField k =
         IntMap.findWithDefault
           (invalidField k)

From 50d2be4636b274cb2495e8ca2fd25301053c12cf Mon Sep 17 00:00:00 2001
From: Aniket Deshpande <git@aniketd.net>
Date: Tue, 19 May 2026 20:11:05 +0530
Subject: [PATCH 04/13] Add mapSparseField helpers for decodeSparseKeyed

---
 libs/cardano-ledger-binary/CHANGELOG.md       |  1 +
 .../Cardano/Ledger/Binary/Decoding/Decoder.hs | 74 ++++++++++++++++++-
 2 files changed, 73 insertions(+), 2 deletions(-)

diff --git a/libs/cardano-ledger-binary/CHANGELOG.md b/libs/cardano-ledger-binary/CHANGELOG.md
index d67e21e9fe6..49e39839fe1 100644
--- a/libs/cardano-ledger-binary/CHANGELOG.md
+++ b/libs/cardano-ledger-binary/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 ## 1.9.0.0
 
+* Add `mapSparseField`, `mapSparseFieldA`, `mapSparseFieldOptional`, `mapSparseFieldGuarded`
 * Add `decodeSparseKeyed`
 * Add `decodeIntegralRational`
 * Add `decodeNonEmptySetLikeEnforceNoDuplicates`
diff --git a/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs b/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
index e8ea8dcd506..625264ceb27 100644
--- a/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
+++ b/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
@@ -80,6 +80,10 @@ module Cardano.Ledger.Binary.Decoding.Decoder (
   decodeListLikeEnforceNoDuplicates,
   decodeMapContents,
   decodeSparseKeyed,
+  mapSparseField,
+  mapSparseFieldA,
+  mapSparseFieldOptional,
+  mapSparseFieldGuarded,
 
   -- **** Applicaitve
   decodeMapTraverse,
@@ -1194,7 +1198,7 @@ decodeMapContentsTraverse decodeKey decodeValue =
 decodeSparseKeyed ::
   forall a s.
   -- | Type name used in error messages.
-  Text.Text ->
+  String ->
   -- | Required keys with friendly names per key. After the map is fully
   -- consumed, the absence of any key in this list is reported as a
   -- failure using its name and key.
@@ -1222,7 +1226,7 @@ decodeSparseKeyed name requiredFields initial decoderForKey = do
   pure acc
   where
     failMsg :: String -> Decoder s b
-    failMsg msg = fail $ Text.unpack name <> ":" <> msg
+    failMsg msg = fail $ name <> ":" <> msg
 
     defLoop :: Set.Set Word -> a -> Int -> Decoder s (Set.Set Word, a)
     defLoop !seen !acc !i
@@ -1252,6 +1256,72 @@ decodeSparseKeyed name requiredFields initial decoderForKey = do
     {-# INLINE step #-}
 {-# INLINE decodeSparseKeyed #-}
 
+-- | Decode a value and apply it to a 'Functor'-wrapped accumulator
+-- (typically 'Annotator'). Intended for use inside the per-key handler
+-- of 'decodeSparseKeyed'.
+mapSparseField ::
+  Functor ann =>
+  -- | Setter that updates the underlying record with the decoded value.
+  (x -> t -> t) ->
+  -- | Decoder for the field value.
+  Decoder s x ->
+  -- | Current accumulator.
+  ann t ->
+  Decoder s (ann t)
+mapSparseField setter dec acc = do
+  !x <- dec
+  pure $ setter x <$> acc
+{-# INLINE mapSparseField #-}
+
+-- | Like 'mapSparseField' but the decoder yields an
+-- 'Applicative'-wrapped value (e.g. @'Annotator' x@).
+mapSparseFieldA ::
+  Applicative ann =>
+  (x -> t -> t) ->
+  Decoder s (ann x) ->
+  ann t ->
+  Decoder s (ann t)
+mapSparseFieldA setter dec acc = do
+  !x <- dec
+  pure $ setter <$> x <*> acc
+{-# INLINE mapSparseFieldA #-}
+
+-- | Like 'mapSparseField' but the setter expects a 'StrictMaybe' value.
+-- Useful when the underlying field is a @'Lens'' t ('StrictMaybe' x)@
+-- and the key's absence implies 'SNothing' (already set by the initial
+-- accumulator).
+mapSparseFieldOptional ::
+  Functor ann =>
+  (StrictMaybe x -> t -> t) ->
+  Decoder s x ->
+  ann t ->
+  Decoder s (ann t)
+mapSparseFieldOptional setter dec acc = do
+  !x <- dec
+  pure $ setter (SJust x) <$> acc
+{-# INLINE mapSparseFieldOptional #-}
+
+-- | Like 'mapSparseField' but reject the value when the predicate is
+-- satisfied.
+mapSparseFieldGuarded ::
+  Functor ann =>
+  -- | Type name; failure is prefixed with @name:@.
+  String ->
+  -- | Error message used when the predicate rejects the value.
+  String ->
+  -- | Predicate: 'True' means reject.
+  (x -> Bool) ->
+  (x -> t -> t) ->
+  Decoder s x ->
+  ann t ->
+  Decoder s (ann t)
+mapSparseFieldGuarded name msg reject setter dec acc = do
+  !x <- dec
+  if reject x
+    then fail $ name <> ":" <> msg
+    else pure $ setter x <$> acc
+{-# INLINE mapSparseFieldGuarded #-}
+
 --------------------------------------------------------------------------------
 -- Time
 --------------------------------------------------------------------------------

From 11d144726db09dd979423a932c694ba532616502 Mon Sep 17 00:00:00 2001
From: Aniket Deshpande <git@aniketd.net>
Date: Tue, 19 May 2026 20:15:02 +0530
Subject: [PATCH 05/13] Use decodeSparseKeyed for AlonzoTxWits PV12+

---
 .../src/Cardano/Ledger/Alonzo/TxAuxData.hs    |  8 ++-
 .../impl/src/Cardano/Ledger/Alonzo/TxWits.hs  | 58 +++++++++++++++----
 2 files changed, 51 insertions(+), 15 deletions(-)

diff --git a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
index 4d1610b03dc..ddf85d41215 100644
--- a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
+++ b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
@@ -96,9 +96,10 @@ import qualified Data.List.NonEmpty as NE
 import Data.Map (Map)
 import qualified Data.Map.Strict as Map
 import Data.Maybe (isNothing, mapMaybe)
+import Data.Proxy (Proxy (..))
 import Data.Sequence.Strict (StrictSeq ((:<|)))
 import qualified Data.Sequence.Strict as StrictSeq
-import Data.Typeable (Typeable)
+import Data.Typeable (Typeable, typeRep)
 import Data.Word (Word64)
 import GHC.Generics (Generic)
 import GHC.Stack
@@ -210,7 +211,7 @@ instance
           ( do
               assertTag 259
               decodeSparseKeyed
-                "AlonzoTxAuxData"
+                name
                 []
                 (pure emptyAlonzoTxAuxDataRaw)
                 decoderForKey
@@ -218,6 +219,7 @@ instance
           decodeAlonzo
       )
     where
+      name = show . typeRep $ Proxy @(AlonzoTxAuxDataRaw era)
       decodeShelley =
         decode
           ( Ann (Emit AlonzoTxAuxDataRaw)
@@ -241,7 +243,7 @@ instance
       decodeAlonzo =
         decode $
           TagD 259 $
-            SparseKeyed "AlonzoTxAuxData" (pure emptyAlonzoTxAuxDataRaw) auxDataField []
+            SparseKeyed name (pure emptyAlonzoTxAuxDataRaw) auxDataField []
 
       decoderForKey ::
         Annotator (AlonzoTxAuxDataRaw era) ->
diff --git a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs
index 52a0e3ca9b8..d41b8f33f74 100644
--- a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs
+++ b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs
@@ -83,12 +83,15 @@ import Cardano.Ledger.Binary (
   decodeNonEmptyList,
   decodeNonEmptySetLikeEnforceNoDuplicates,
   decodeNonEmptySetLikeEnforceNoDuplicatesAnn,
+  decodeSparseKeyed,
   encodeFoldableEncoder,
   encodeListLen,
   encodeTag,
   ifDecoderVersionAtLeast,
   ifEncodingVersionAtLeast,
   listLenInt,
+  mapSparseField,
+  mapSparseFieldA,
   natVersion,
   peekTokenType,
   setTag,
@@ -129,8 +132,10 @@ import qualified Data.Map.Strict as Map
 import Data.MapExtras (fromElems)
 import qualified Data.MapExtras as Map (fromElems)
 import Data.Maybe (mapMaybe)
+import Data.Proxy (Proxy (..))
 import Data.Set (Set)
 import qualified Data.Set as Set
+import Data.Typeable (typeRep)
 import GHC.Generics (Generic)
 import Lens.Micro
 import NoThunks.Class (NoThunks)
@@ -601,13 +606,12 @@ instance
   DecCBOR (Annotator (AlonzoTxWitsRaw era))
   where
   decCBOR =
-    decode $
-      SparseKeyed
-        "AlonzoTxWits"
-        (pure emptyTxWitsRaw)
-        txWitnessField
-        []
+    ifDecoderVersionAtLeast
+      (natVersion @12)
+      (decodeSparseKeyed name [] (pure emptyTxWitsRaw) decoderForKey)
+      (decode $ SparseKeyed name (pure emptyTxWitsRaw) txWitnessField [])
     where
+      name = show . typeRep $ Proxy @(AlonzoTxWitsRaw era)
       addrWitsSetDecoder :: (Ord a, DecCBOR a) => Decoder s (Set a)
       addrWitsSetDecoder = do
         let
@@ -621,6 +625,30 @@ instance
         ifDecoderVersionAtLeast (natVersion @12) nonEmptyNoDuplicatesDecoder nonEmptyDecoder
       {-# INLINE addrWitsSetDecoder #-}
 
+      setOrListDecoder :: (Ord a, DecCBOR a) => Decoder s (Set a)
+      setOrListDecoder =
+        ifDecoderVersionAtLeast
+          (natVersion @9)
+          addrWitsSetDecoder
+          (Set.fromList <$> decodeList decCBOR)
+      {-# INLINE setOrListDecoder #-}
+
+      decoderForKey ::
+        Annotator (AlonzoTxWitsRaw era) ->
+        Word ->
+        Maybe (Decoder s (Annotator (AlonzoTxWitsRaw era)))
+      decoderForKey acc = \case
+        0 -> Just $ mapSparseField (\x w -> w {atwrAddrTxWits = x}) setOrListDecoder acc
+        1 -> Just $ mapSparseFieldA addScriptsTxWitsRaw nativeScriptsDecoder acc
+        2 -> Just $ mapSparseField (\x w -> w {atwrBootAddrTxWits = x}) setOrListDecoder acc
+        3 -> Just $ mapSparseField addScriptsTxWitsRaw (alonzoPlutusScriptDecoder SPlutusV1) acc
+        4 -> Just $ mapSparseFieldA (\x w -> w {atwrDatsTxWits = x}) decCBOR acc
+        5 -> Just $ mapSparseFieldA (\x w -> w {atwrRdmrsTxWits = x}) decCBOR acc
+        6 -> Just $ mapSparseField addScriptsTxWitsRaw (alonzoPlutusScriptDecoder SPlutusV2) acc
+        7 -> Just $ mapSparseField addScriptsTxWitsRaw (alonzoPlutusScriptDecoder SPlutusV3) acc
+        _ -> Nothing
+      {-# INLINE decoderForKey #-}
+
       txWitnessField :: Word -> Field (Annotator (AlonzoTxWitsRaw era))
       txWitnessField 0 =
         fieldA
@@ -698,14 +726,20 @@ decodeAlonzoPlutusScript ::
   (AlonzoEraScript era, PlutusLanguage l) =>
   SLanguage l ->
   Decode (Closed Dense) (Map ScriptHash (Script era))
-decodeAlonzoPlutusScript slang =
-  D $
-    ifDecoderVersionAtLeast
-      (natVersion @9)
-      (scriptDecoderV9 (fromPlutusScript <$> decodePlutusScript slang))
-      (scriptDecoder (fromPlutusScript <$> decodePlutusScript slang))
+decodeAlonzoPlutusScript slang = D (alonzoPlutusScriptDecoder slang)
 {-# INLINE decodeAlonzoPlutusScript #-}
 
+alonzoPlutusScriptDecoder ::
+  (AlonzoEraScript era, PlutusLanguage l) =>
+  SLanguage l ->
+  Decoder s (Map ScriptHash (Script era))
+alonzoPlutusScriptDecoder slang =
+  ifDecoderVersionAtLeast
+    (natVersion @9)
+    (scriptDecoderV9 (fromPlutusScript <$> decodePlutusScript slang))
+    (scriptDecoder (fromPlutusScript <$> decodePlutusScript slang))
+{-# INLINE alonzoPlutusScriptDecoder #-}
+
 scriptDecoderV9 ::
   EraScript era =>
   Decoder s (Script era) ->

From 45e4a2e3473ecac9b4fe37d23b1a7bc360a63c1f Mon Sep 17 00:00:00 2001
From: Aniket Deshpande <git@aniketd.net>
Date: Tue, 19 May 2026 20:33:58 +0530
Subject: [PATCH 06/13]  Use decodeSparseKeyed for DijkstraTxBody

---
 .../impl/src/Cardano/Ledger/Babbage/TxOut.hs  |   7 +-
 .../src/Cardano/Ledger/Dijkstra/TxBody.hs     | 215 +++++++++++-------
 2 files changed, 140 insertions(+), 82 deletions(-)

diff --git a/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs b/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs
index 4e41eb5fd5c..41db07e242a 100644
--- a/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs
+++ b/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs
@@ -116,7 +116,7 @@ import qualified Data.ByteString.Lazy as LBS
 import Data.Maybe (fromMaybe)
 import Data.MemPack
 import qualified Data.Text as T
-import Data.Typeable (Proxy (..))
+import Data.Typeable (Proxy (..), typeRep)
 import GHC.Generics (Generic)
 import GHC.Stack (HasCallStack)
 import Lens.Micro (Lens', lens, to, (^.))
@@ -610,14 +610,15 @@ decodeTxOut decAddr = do
   dtxo <-
     ifDecoderVersionAtLeast
       (natVersion @12)
-      (decodeSparseKeyed "TxOut" requiredFields initial decoderForKey)
-      (decode $ SparseKeyed "TxOut" initial bodyFields requiredFields)
+      (decodeSparseKeyed name requiredFields initial decoderForKey)
+      (decode $ SparseKeyed name initial bodyFields requiredFields)
   case dtxo of
     DecodingTxOut SNothing _ _ _ ->
       cborError $ DecoderErrorCustom "BabbageTxOut" "Impossible: no Addr"
     DecodingTxOut (SJust (addr, cAddr)) val d script ->
       pure $ mkTxOut addr cAddr val d script
   where
+    name = show . typeRep $ Proxy @(BabbageTxOut era)
     initial :: DecodingTxOut era
     initial = DecodingTxOut SNothing mempty NoDatum SNothing
     decoderForKey :: DecodingTxOut era -> Word -> Maybe (Decoder s (DecodingTxOut era))
diff --git a/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs b/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs
index fedf5aba08b..1f573b35625 100644
--- a/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs
+++ b/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs
@@ -106,7 +106,7 @@ import Cardano.Ledger.Babbage.TxBody (
   babbageAllInputsTxBodyF,
   babbageSpendableInputsTxBodyF,
  )
-import Cardano.Ledger.BaseTypes (Network, StrictMaybe (..), fromSMaybe)
+import Cardano.Ledger.BaseTypes (Network, StrictMaybe (..))
 import Cardano.Ledger.Binary
 import Cardano.Ledger.Binary.Coders
 import Cardano.Ledger.Coin (Coin, decodePositiveCoin)
@@ -150,11 +150,12 @@ import Data.OMap.Strict (OMap)
 import qualified Data.OMap.Strict as OMap
 import Data.OSet.Strict (OSet, decodeOSet)
 import qualified Data.OSet.Strict as OSet
+import Data.Proxy (Proxy (..))
 import Data.STRef (newSTRef, readSTRef, writeSTRef)
 import Data.Sequence.Strict (StrictSeq)
 import Data.Set (Set, foldr')
 import qualified Data.Set as Set
-import Data.Typeable (Typeable)
+import Data.Typeable (Typeable, typeRep)
 import GHC.Generics (Generic)
 import Lens.Micro (Lens', lens, to, (.~), (^.))
 import NoThunks.Class (InspectHeap (..), NoThunks)
@@ -327,104 +328,160 @@ instance
   DecCBOR (Annotator (DijkstraTxBodyRaw l era))
   where
   decCBOR = withSTxBothLevels @l $ \sTxLevel ->
-    decode $
-      SparseKeyed
-        "TxBodyRaw"
-        (pure $ basicDijkstraTxBodyRaw sTxLevel)
-        (bodyFields sTxLevel)
-        (requiredFields sTxLevel)
+    decodeSparseKeyed
+      name
+      (requiredFields sTxLevel)
+      (pure $ basicDijkstraTxBodyRaw sTxLevel)
+      (decoderForKey sTxLevel)
     where
-      bodyFields :: STxBothLevels l era -> Word -> Field (Annotator (DijkstraTxBodyRaw l era))
-      bodyFields sTxLevel = \case
-        0 -> fieldA (inputsDijkstraTxBodyRawL .~) From
-        1 -> fieldA (outputsDijkstraTxBodyRawL .~) From
-        2 | STopTx <- sTxLevel -> fieldA (feeDijkstraTxBodyRawL .~) From
-        3 -> ofieldA (vldtDijkstraTxBodyRawL . invalidHereAfterL .~) From
+      name = show . typeRep $ Proxy @(DijkstraTxBodyRaw l era)
+      decoderForKey ::
+        STxBothLevels l era ->
+        Annotator (DijkstraTxBodyRaw l era) ->
+        Word ->
+        Maybe (Decoder s (Annotator (DijkstraTxBodyRaw l era)))
+      decoderForKey sTxLevel acc = \case
+        0 -> Just $ mapSparseField (inputsDijkstraTxBodyRawL .~) decCBOR acc
+        1 -> Just $ mapSparseField (outputsDijkstraTxBodyRawL .~) decCBOR acc
+        2 | STopTx <- sTxLevel -> Just $ mapSparseField (feeDijkstraTxBodyRawL .~) decCBOR acc
+        3 -> Just $ mapSparseFieldOptional (vldtDijkstraTxBodyRawL . invalidHereAfterL .~) decCBOR acc
         4 ->
-          fieldAGuarded
-            (emptyFailure "Certificates" "non-empty")
-            OSet.null
-            (certsDijkstraTxBodyRawL .~)
-            From
+          Just $
+            mapSparseFieldGuarded
+              name
+              (emptyFailure "Certificates" "non-empty")
+              OSet.null
+              (certsDijkstraTxBodyRawL .~)
+              decCBOR
+              acc
         5 ->
-          fieldAGuarded
-            (emptyFailure "Withdrawals" "non-empty")
-            (null . unWithdrawals)
-            (withdrawalsDijkstraTxBodyRawL .~)
-            From
-        7 -> ofieldA (auxDataHashDijkstraTxBodyRawL .~) From
-        8 -> ofieldA (vldtDijkstraTxBodyRawL . invalidBeforeL .~) From
+          Just $
+            mapSparseFieldGuarded
+              name
+              (emptyFailure "Withdrawals" "non-empty")
+              (null . unWithdrawals)
+              (withdrawalsDijkstraTxBodyRawL .~)
+              decCBOR
+              acc
+        7 -> Just $ mapSparseFieldOptional (auxDataHashDijkstraTxBodyRawL .~) decCBOR acc
+        8 -> Just $ mapSparseFieldOptional (vldtDijkstraTxBodyRawL . invalidBeforeL .~) decCBOR acc
         9 ->
-          fieldAGuarded
-            (emptyFailure "Mint" "non-empty")
-            (== mempty)
-            (mintDijkstraTxBodyRawL .~)
-            From
-        11 -> ofieldA (scriptIntegrityHashDijkstraTxBodyRawL .~) From
+          Just $
+            mapSparseFieldGuarded
+              name
+              (emptyFailure "Mint" "non-empty")
+              (== mempty)
+              (mintDijkstraTxBodyRawL .~)
+              decCBOR
+              acc
+        11 -> Just $ mapSparseFieldOptional (scriptIntegrityHashDijkstraTxBodyRawL .~) decCBOR acc
         13
           | STopTx <- sTxLevel ->
-              fieldAGuarded
-                (emptyFailure "Collateral Inputs" "non-empty")
-                null
-                (collateralInputsDijkstraTxBodyRawL .~)
-                From
+              Just $
+                mapSparseFieldGuarded
+                  name
+                  (emptyFailure "Collateral Inputs" "non-empty")
+                  null
+                  (collateralInputsDijkstraTxBodyRawL .~)
+                  decCBOR
+                  acc
+        -- Keys 14 and 22 are decoded with 'mapSparseField' directly.
+        -- Their lenses target plain values (@'OSet' (Credential Guard)@
+        -- and @'Coin'@), so there's no 'StrictMaybe' to wrap or unwrap.
+        --
+        -- The round-trip stays consistent and symmetric because
+        -- the encoder omits each key when its value equals the
+        -- default, and the decoder's initial accumulator (built by
+        -- 'basicDijkstraTxBodyRaw') starts each field at that same
+        -- default.
+        --
+        -- For example:
+        --   * Key 14 — encoder: @Omit null (Key 14 (To dtbrGuards))@.
+        --   The key is in the serialised bits only when @dtbrGuards@
+        --   is non-empty. The accumulator starts at @mempty@, so a
+        --   missing key keeps the field at @mempty@ — matching what
+        --   the sender skipped.
+        --
+        --   * Key 22 — encoder: @Omit (== mempty) (Key 22 (To
+        --   dtbrTreasuryDonation))@. The key is in the serialised bits
+        --   only when the donation is non-zero. The accumulator starts
+        --   at @mempty@, so a missing key keeps the field at @zero@.
         14 ->
-          ofieldA
-            (\x -> guardsDijkstraTxBodyRawL .~ fromSMaybe mempty x)
-            (D decodeGuards)
-        15 -> ofieldA (networkIdDijkstraTxBodyRawL .~) From
+          Just $ mapSparseField (guardsDijkstraTxBodyRawL .~) decodeGuards acc
+        15 -> Just $ mapSparseFieldOptional (networkIdDijkstraTxBodyRawL .~) decCBOR acc
         16
           | STopTx <- sTxLevel ->
-              ofieldA (collateralReturnDijkstraTxBodyRawL .~) From
+              Just $ mapSparseFieldOptional (collateralReturnDijkstraTxBodyRawL .~) decCBOR acc
         17
           | STopTx <- sTxLevel ->
-              ofieldA (totalCollateralDijkstraTxBodyRawL .~) From
+              Just $ mapSparseFieldOptional (totalCollateralDijkstraTxBodyRawL .~) decCBOR acc
         18 ->
-          fieldAGuarded
-            (emptyFailure "Reference Inputs" "non-empty")
-            null
-            (referenceInputsDijkstraTxBodyRawL .~)
-            From
+          Just $
+            mapSparseFieldGuarded
+              name
+              (emptyFailure "Reference Inputs" "non-empty")
+              null
+              (referenceInputsDijkstraTxBodyRawL .~)
+              decCBOR
+              acc
         19 ->
-          fieldAGuarded
-            (emptyFailure "VotingProcedures" "non-empty")
-            (null . unVotingProcedures)
-            (votingProceduresDijkstraTxBodyRawL .~)
-            From
+          Just $
+            mapSparseFieldGuarded
+              name
+              (emptyFailure "VotingProcedures" "non-empty")
+              (null . unVotingProcedures)
+              (votingProceduresDijkstraTxBodyRawL .~)
+              decCBOR
+              acc
         20 ->
-          fieldAGuarded
-            (emptyFailure "ProposalProcedures" "non-empty")
-            OSet.null
-            (proposalProceduresDijkstraTxBodyRawL .~)
-            From
-        21 -> ofieldA (currentTreasuryValueDijkstraTxBodyRawL .~) From
+          Just $
+            mapSparseFieldGuarded
+              name
+              (emptyFailure "ProposalProcedures" "non-empty")
+              OSet.null
+              (proposalProceduresDijkstraTxBodyRawL .~)
+              decCBOR
+              acc
+        21 -> Just $ mapSparseFieldOptional (currentTreasuryValueDijkstraTxBodyRawL .~) decCBOR acc
         22 ->
-          ofieldA
-            (\x -> treasuryDonationDijkstraTxBodyRawL .~ fromSMaybe zero x)
-            (D (decodePositiveCoin $ emptyFailure "Treasury Donation" "non-zero"))
+          -- See comment about field 14.
+          Just $
+            mapSparseField
+              (treasuryDonationDijkstraTxBodyRawL .~)
+              (decodePositiveCoin $ emptyFailure "Treasury Donation" "non-zero")
+              acc
         23
           | STopTx <- sTxLevel ->
-              fieldAA (subTransactionsDijkstraTxBodyRawL .~) (D decodeSubTransactions)
+              Just $ mapSparseFieldA (subTransactionsDijkstraTxBodyRawL .~) decodeSubTransactions acc
         24
           | SSubTx <- sTxLevel ->
-              fieldAGuarded
-                (emptyFailure "RequiredTopLevelGuards" "non-empty")
-                Map.null
-                (requiredTopLevelGuardsDijkstraTxBodyRawL .~)
-                (D (decodeMap decCBOR (decodeNullStrictMaybe decCBOR)))
+              Just $
+                mapSparseFieldGuarded
+                  name
+                  (emptyFailure "RequiredTopLevelGuards" "non-empty")
+                  Map.null
+                  (requiredTopLevelGuardsDijkstraTxBodyRawL .~)
+                  (decodeMap decCBOR (decodeNullStrictMaybe decCBOR))
+                  acc
         25 ->
-          fieldAGuarded
-            (emptyFailure "DirectDeposits" "non-empty")
-            (null . unDirectDeposits)
-            (directDepositsDijkstraTxBodyRawL .~)
-            From
+          Just $
+            mapSparseFieldGuarded
+              name
+              (emptyFailure "DirectDeposits" "non-empty")
+              (null . unDirectDeposits)
+              (directDepositsDijkstraTxBodyRawL .~)
+              decCBOR
+              acc
         26 ->
-          fieldAGuarded
-            (emptyFailure "AccountBalanceIntervals" "non-empty")
-            (null . unAccountBalanceIntervals)
-            (accountBalanceIntervalsDijkstraTxBodyRawL .~)
-            From
-        n -> invalidField n
+          Just $
+            mapSparseFieldGuarded
+              name
+              (emptyFailure "AccountBalanceIntervals" "non-empty")
+              (null . unAccountBalanceIntervals)
+              (accountBalanceIntervalsDijkstraTxBodyRawL .~)
+              decCBOR
+              acc
+        _ -> Nothing
       decodeSubTransactions :: Decoder s (Annotator (OMap TxId (Tx SubTx era)))
       decodeSubTransactions =
         decodeNonEmptySetLikeEnforceNoDuplicatesAnn

From da6c95e909239c2832b0e07d96c53affb580458f Mon Sep 17 00:00:00 2001
From: Aniket Deshpande <git@aniketd.net>
Date: Wed, 20 May 2026 16:20:28 +0530
Subject: [PATCH 07/13] Fix test with new error report

---
 .../Test/Cardano/Ledger/Alonzo/Binary/Golden.hs       | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/eras/alonzo/impl/testlib/Test/Cardano/Ledger/Alonzo/Binary/Golden.hs b/eras/alonzo/impl/testlib/Test/Cardano/Ledger/Alonzo/Binary/Golden.hs
index 4ec1b3b3475..55ecb67b60d 100644
--- a/eras/alonzo/impl/testlib/Test/Cardano/Ledger/Alonzo/Binary/Golden.hs
+++ b/eras/alonzo/impl/testlib/Test/Cardano/Ledger/Alonzo/Binary/Golden.hs
@@ -15,16 +15,18 @@ module Test.Cardano.Ledger.Alonzo.Binary.Golden (
 ) where
 
 import Cardano.Ledger.Alonzo.Core (EraTxWits (..), ShelleyEraTxCert)
+import Cardano.Ledger.Alonzo.TxWits (AlonzoTxWitsRaw)
 import Cardano.Ledger.Binary (
   Annotator,
   DecoderError (..),
   DeserialiseFailure (..),
   Tokens (..),
   Version,
+  natVersion,
  )
 import qualified Cardano.Ledger.Binary as Binary
 import Cardano.Ledger.MemoBytes (EqRaw (..))
-import Data.Data (Proxy (..))
+import Data.Data (Proxy (..), typeRep)
 import Data.Void (Void)
 import Test.Cardano.Ledger.Allegra.Binary.Golden hiding (spec)
 import Test.Cardano.Ledger.Alonzo.Era (AlonzoEraTest)
@@ -77,13 +79,16 @@ txWitsDecodingFailsOnInvalidField version validFields =
           DecoderErrorDeserialiseFailure
             lbl
             ( DeserialiseFailure (if n >= 24 then 3 else 2) $
-                -- TODO fix the `occured` typo in the produced value
-                "An error occured while decoding (Int,Void) not a valid key:.\nError: " <> show n
+                if version >= natVersion @12
+                  then typeName <> ":Unknown field key " <> show n
+                  -- TODO fix the `occured` typo in the produced value
+                  else "An error occured while decoding (Int,Void) not a valid key:.\nError: " <> show n
             )
         else
           DecoderErrorDeserialiseFailure lbl (DeserialiseFailure 1 "expected word")
   where
     lbl = Binary.label $ Proxy @(Annotator (TxWits era))
+    typeName = show (typeRep (Proxy @(AlonzoTxWitsRaw era)))
 
 spec ::
   forall era.

From 9260354246381100289d0241f51bd415557a0b4f Mon Sep 17 00:00:00 2001
From: Aniket Deshpande <git@aniketd.net>
Date: Wed, 20 May 2026 19:37:03 +0530
Subject: [PATCH 08/13] Rename all decoderForKey to decoderByKey

---
 eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs   | 8 ++++----
 eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs      | 8 ++++----
 eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs     | 8 ++++----
 eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs  | 6 +++---
 .../src/Cardano/Ledger/Binary/Decoding/Decoder.hs         | 4 ++--
 .../src/Cardano/Ledger/Core/PParams.hs                    | 6 +++---
 6 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
index ddf85d41215..45cc56a94f9 100644
--- a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
+++ b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
@@ -214,7 +214,7 @@ instance
                 name
                 []
                 (pure emptyAlonzoTxAuxDataRaw)
-                decoderForKey
+                decoderByKey
           )
           decodeAlonzo
       )
@@ -245,11 +245,11 @@ instance
           TagD 259 $
             SparseKeyed name (pure emptyAlonzoTxAuxDataRaw) auxDataField []
 
-      decoderForKey ::
+      decoderByKey ::
         Annotator (AlonzoTxAuxDataRaw era) ->
         Word ->
         Maybe (Decoder s (Annotator (AlonzoTxAuxDataRaw era)))
-      decoderForKey acc = \case
+      decoderByKey acc = \case
         0 -> Just $ do
           !x <- decCBOR
           pure $ (\ad -> ad {atadrMetadata = x}) <$> acc
@@ -276,7 +276,7 @@ instance
           !x <- decCBOR
           pure $ addPlutusScripts PlutusV4 x <$> acc
         _ -> Nothing
-      {-# INLINE decoderForKey #-}
+      {-# INLINE decoderByKey #-}
 
       auxDataField :: Word -> Field (Annotator (AlonzoTxAuxDataRaw era))
       auxDataField 0 = fieldA (\x ad -> ad {atadrMetadata = x}) From
diff --git a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs
index d41b8f33f74..887ce809c0c 100644
--- a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs
+++ b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs
@@ -608,7 +608,7 @@ instance
   decCBOR =
     ifDecoderVersionAtLeast
       (natVersion @12)
-      (decodeSparseKeyed name [] (pure emptyTxWitsRaw) decoderForKey)
+      (decodeSparseKeyed name [] (pure emptyTxWitsRaw) decoderByKey)
       (decode $ SparseKeyed name (pure emptyTxWitsRaw) txWitnessField [])
     where
       name = show . typeRep $ Proxy @(AlonzoTxWitsRaw era)
@@ -633,11 +633,11 @@ instance
           (Set.fromList <$> decodeList decCBOR)
       {-# INLINE setOrListDecoder #-}
 
-      decoderForKey ::
+      decoderByKey ::
         Annotator (AlonzoTxWitsRaw era) ->
         Word ->
         Maybe (Decoder s (Annotator (AlonzoTxWitsRaw era)))
-      decoderForKey acc = \case
+      decoderByKey acc = \case
         0 -> Just $ mapSparseField (\x w -> w {atwrAddrTxWits = x}) setOrListDecoder acc
         1 -> Just $ mapSparseFieldA addScriptsTxWitsRaw nativeScriptsDecoder acc
         2 -> Just $ mapSparseField (\x w -> w {atwrBootAddrTxWits = x}) setOrListDecoder acc
@@ -647,7 +647,7 @@ instance
         6 -> Just $ mapSparseField addScriptsTxWitsRaw (alonzoPlutusScriptDecoder SPlutusV2) acc
         7 -> Just $ mapSparseField addScriptsTxWitsRaw (alonzoPlutusScriptDecoder SPlutusV3) acc
         _ -> Nothing
-      {-# INLINE decoderForKey #-}
+      {-# INLINE decoderByKey #-}
 
       txWitnessField :: Word -> Field (Annotator (AlonzoTxWitsRaw era))
       txWitnessField 0 =
diff --git a/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs b/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs
index 41db07e242a..ccff38badfb 100644
--- a/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs
+++ b/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs
@@ -610,7 +610,7 @@ decodeTxOut decAddr = do
   dtxo <-
     ifDecoderVersionAtLeast
       (natVersion @12)
-      (decodeSparseKeyed name requiredFields initial decoderForKey)
+      (decodeSparseKeyed name requiredFields initial decoderByKey)
       (decode $ SparseKeyed name initial bodyFields requiredFields)
   case dtxo of
     DecodingTxOut SNothing _ _ _ ->
@@ -621,8 +621,8 @@ decodeTxOut decAddr = do
     name = show . typeRep $ Proxy @(BabbageTxOut era)
     initial :: DecodingTxOut era
     initial = DecodingTxOut SNothing mempty NoDatum SNothing
-    decoderForKey :: DecodingTxOut era -> Word -> Maybe (Decoder s (DecodingTxOut era))
-    decoderForKey txOut = \case
+    decoderByKey :: DecodingTxOut era -> Word -> Maybe (Decoder s (DecodingTxOut era))
+    decoderByKey txOut = \case
       0 -> Just $ do
         !x <- decAddr
         pure txOut {decodingTxOutAddr = SJust x}
@@ -636,7 +636,7 @@ decodeTxOut decAddr = do
         !x <- decodeCIC "Script"
         pure txOut {decodingTxOutScript = SJust x}
       _ -> Nothing
-    {-# INLINE decoderForKey #-}
+    {-# INLINE decoderByKey #-}
     bodyFields :: (Word -> Field (DecodingTxOut era))
     bodyFields 0 =
       field
diff --git a/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs b/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs
index 1f573b35625..e907a070e05 100644
--- a/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs
+++ b/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs
@@ -332,15 +332,15 @@ instance
       name
       (requiredFields sTxLevel)
       (pure $ basicDijkstraTxBodyRaw sTxLevel)
-      (decoderForKey sTxLevel)
+      (decoderByKey sTxLevel)
     where
       name = show . typeRep $ Proxy @(DijkstraTxBodyRaw l era)
-      decoderForKey ::
+      decoderByKey ::
         STxBothLevels l era ->
         Annotator (DijkstraTxBodyRaw l era) ->
         Word ->
         Maybe (Decoder s (Annotator (DijkstraTxBodyRaw l era)))
-      decoderForKey sTxLevel acc = \case
+      decoderByKey sTxLevel acc = \case
         0 -> Just $ mapSparseField (inputsDijkstraTxBodyRawL .~) decCBOR acc
         1 -> Just $ mapSparseField (outputsDijkstraTxBodyRawL .~) decCBOR acc
         2 | STopTx <- sTxLevel -> Just $ mapSparseField (feeDijkstraTxBodyRawL .~) decCBOR acc
diff --git a/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs b/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
index 625264ceb27..87ff8d43441 100644
--- a/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
+++ b/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
@@ -1210,7 +1210,7 @@ decodeSparseKeyed ::
   -- indicates the key as unknown and is reported as decoding failure.
   (a -> Word -> Maybe (Decoder s a)) ->
   Decoder s a
-decodeSparseKeyed name requiredFields initial decoderForKey = do
+decodeSparseKeyed name requiredFields initial decoderByKey = do
   (seen, acc) <-
     decodeMapLenOrIndef >>= \case
       Just len -> defLoop Set.empty initial len
@@ -1248,7 +1248,7 @@ decodeSparseKeyed name requiredFields initial decoderForKey = do
       key <- decodeWord
       if Set.member key seen
         then failMsg $ "Duplicate field key " <> show key
-        else case decoderForKey acc key of
+        else case decoderByKey acc key of
           Nothing -> failMsg $ "Unknown field key " <> show key
           Just decoder -> do
             acc' <- decoder
diff --git a/libs/cardano-ledger-core/src/Cardano/Ledger/Core/PParams.hs b/libs/cardano-ledger-core/src/Cardano/Ledger/Core/PParams.hs
index 9017ff0ee26..ed2b920964d 100644
--- a/libs/cardano-ledger-core/src/Cardano/Ledger/Core/PParams.hs
+++ b/libs/cardano-ledger-core/src/Cardano/Ledger/Core/PParams.hs
@@ -257,15 +257,15 @@ instance EraPParams era => DecCBOR (PParamsUpdate era) where
   decCBOR =
     ifDecoderVersionAtLeast
       (natVersion @12)
-      (decodeSparseKeyed name [] emptyPParamsUpdate decoderForKey)
+      (decodeSparseKeyed name [] emptyPParamsUpdate decoderByKey)
       (decode $ SparseKeyed name emptyPParamsUpdate updateField [])
     where
       name = show . typeRep $ Proxy @(PParamsUpdate era)
-      decoderForKey ::
+      decoderByKey ::
         PParamsUpdate era ->
         Word ->
         Maybe (Decoder s (PParamsUpdate era))
-      decoderForKey acc k =
+      decoderByKey acc k =
         case IntMap.lookup (fromIntegral k) updateFieldMap of
           Just (Field setter dec) -> Just $ (`setter` acc) <$> dec
           Nothing -> Nothing

From 2a030c271b4a86d2ed6c7cf9017c3055bd15d91b Mon Sep 17 00:00:00 2001
From: Aniket Deshpande <git@aniketd.net>
Date: Thu, 21 May 2026 21:23:14 +0530
Subject: [PATCH 09/13] decodeSparseKeyed take TypeName instead of String.

Update AlonzoTxAuxData, AlonzoTxWits, BabbageTxOut, DijkstraTxBody,
and PParamsUpdate.

Add decodeAddPlutus helper for AlonzoTxAuxData.
---
 cabal.project                                 |  7 +++++
 .../src/Cardano/Ledger/Alonzo/TxAuxData.hs    | 29 ++++++++-----------
 .../impl/src/Cardano/Ledger/Alonzo/TxWits.hs  |  3 +-
 .../babbage/impl/cardano-ledger-babbage.cabal |  1 +
 .../impl/src/Cardano/Ledger/Babbage/TxOut.hs  |  3 +-
 .../impl/cardano-ledger-dijkstra.cabal        |  1 +
 .../src/Cardano/Ledger/Dijkstra/TxBody.hs     |  3 +-
 .../Cardano/Ledger/Binary/Decoding/Decoder.hs |  5 ++--
 .../src/Cardano/Ledger/Core/PParams.hs        |  3 +-
 9 files changed, 32 insertions(+), 23 deletions(-)

diff --git a/cabal.project b/cabal.project
index b4dfaf52d1b..a23063d9905 100644
--- a/cabal.project
+++ b/cabal.project
@@ -10,6 +10,13 @@ repository cardano-haskell-packages
     c00aae8461a256275598500ea0e187588c35a5d5d7454fb57eac18d9edb86a56
     d4a35cd3121aa00d18544bb0ac01c3e1691d618f462c46129271bccf39f7e8ee
 
+source-repository-package
+  type: git
+  location: https://github.com/IntersectMBO/cardano-base.git
+  subdir: cardano-base
+  --sha256: sha256-Gj8BPEew+UYkCWr3D0LgA6dvhYof49V20XRMRMf1FzY=
+  tag: efe33cb3739f5c90b733b730bdeffa11a75f291d
+
 source-repository-package
   type: git
   location: https://github.com/IntersectMBO/formal-ledger-specifications.git
diff --git a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
index 45cc56a94f9..981a2e7ef3b 100644
--- a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
+++ b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
@@ -50,6 +50,7 @@ module Cardano.Ledger.Alonzo.TxAuxData (
   atadPlutus',
 ) where
 
+import Cardano.Base.Typeable (TypeName (TypeName))
 import Cardano.Ledger.Allegra.TxAuxData (AllegraEraTxAuxData (..))
 import Cardano.Ledger.Alonzo.Era
 import Cardano.Ledger.Alonzo.Scripts (
@@ -211,7 +212,7 @@ instance
           ( do
               assertTag 259
               decodeSparseKeyed
-                name
+                TypeName
                 []
                 (pure emptyAlonzoTxAuxDataRaw)
                 decoderByKey
@@ -259,23 +260,17 @@ instance
             (\scripts ad -> ad {atadrNativeScripts = atadrNativeScripts ad <> scripts})
               <$> x
               <*> acc
-        2 -> Just $ do
-          guardPlutus PlutusV1
-          !x <- decCBOR
-          pure $ addPlutusScripts PlutusV1 x <$> acc
-        3 -> Just $ do
-          guardPlutus PlutusV2
-          !x <- decCBOR
-          pure $ addPlutusScripts PlutusV2 x <$> acc
-        4 -> Just $ do
-          guardPlutus PlutusV3
-          !x <- decCBOR
-          pure $ addPlutusScripts PlutusV3 x <$> acc
-        5 -> Just $ do
-          guardPlutus PlutusV4
-          !x <- decCBOR
-          pure $ addPlutusScripts PlutusV4 x <$> acc
+        2 -> decodeAddPlutus PlutusV1 acc
+        3 -> decodeAddPlutus PlutusV2 acc
+        4 -> decodeAddPlutus PlutusV3 acc
+        5 -> decodeAddPlutus PlutusV4 acc
         _ -> Nothing
+        where
+          decodeAddPlutus lang accu = Just $ do
+            guardPlutus lang
+            !x <- decCBOR
+            pure $ addPlutusScripts lang x <$> accu
+          {-# INLINE decodeAddPlutus #-}
       {-# INLINE decoderByKey #-}
 
       auxDataField :: Word -> Field (Annotator (AlonzoTxAuxDataRaw era))
diff --git a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs
index 887ce809c0c..996938fca6f 100644
--- a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs
+++ b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs
@@ -56,6 +56,7 @@ module Cardano.Ledger.Alonzo.TxWits (
 ) where
 
 import Cardano.Base.Proxy (asProxy)
+import Cardano.Base.Typeable (TypeName (TypeName))
 import Cardano.Ledger.Alonzo.Era (AlonzoEra)
 import Cardano.Ledger.Alonzo.Scripts (
   AlonzoEraScript (..),
@@ -608,7 +609,7 @@ instance
   decCBOR =
     ifDecoderVersionAtLeast
       (natVersion @12)
-      (decodeSparseKeyed name [] (pure emptyTxWitsRaw) decoderByKey)
+      (decodeSparseKeyed TypeName [] (pure emptyTxWitsRaw) decoderByKey)
       (decode $ SparseKeyed name (pure emptyTxWitsRaw) txWitnessField [])
     where
       name = show . typeRep $ Proxy @(AlonzoTxWitsRaw era)
diff --git a/eras/babbage/impl/cardano-ledger-babbage.cabal b/eras/babbage/impl/cardano-ledger-babbage.cabal
index ae7f66a1614..79a76d36a54 100644
--- a/eras/babbage/impl/cardano-ledger-babbage.cabal
+++ b/eras/babbage/impl/cardano-ledger-babbage.cabal
@@ -89,6 +89,7 @@ library
     aeson >=2.2,
     base >=4.18 && <5,
     bytestring,
+    cardano-base >=0.1.4,
     cardano-data >=1.2,
     cardano-ledger-allegra ^>=1.10,
     cardano-ledger-alonzo ^>=1.16,
diff --git a/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs b/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs
index ccff38badfb..33c061ed932 100644
--- a/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs
+++ b/eras/babbage/impl/src/Cardano/Ledger/Babbage/TxOut.hs
@@ -42,6 +42,7 @@ module Cardano.Ledger.Babbage.TxOut (
   internBabbageTxOut,
 ) where
 
+import Cardano.Base.Typeable (TypeName (TypeName))
 import Cardano.Ledger.Address (
   CompactAddr,
   compactAddr,
@@ -610,7 +611,7 @@ decodeTxOut decAddr = do
   dtxo <-
     ifDecoderVersionAtLeast
       (natVersion @12)
-      (decodeSparseKeyed name requiredFields initial decoderByKey)
+      (decodeSparseKeyed TypeName requiredFields initial decoderByKey)
       (decode $ SparseKeyed name initial bodyFields requiredFields)
   case dtxo of
     DecodingTxOut SNothing _ _ _ ->
diff --git a/eras/dijkstra/impl/cardano-ledger-dijkstra.cabal b/eras/dijkstra/impl/cardano-ledger-dijkstra.cabal
index b03f181b990..e9b4310ebdf 100644
--- a/eras/dijkstra/impl/cardano-ledger-dijkstra.cabal
+++ b/eras/dijkstra/impl/cardano-ledger-dijkstra.cabal
@@ -105,6 +105,7 @@ library
     aeson,
     base >=4.14 && <5,
     bytestring,
+    cardano-base >=0.1.4,
     cardano-crypto-class,
     cardano-data ^>=1.3,
     cardano-ledger-allegra,
diff --git a/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs b/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs
index e907a070e05..8ad4dc71659 100644
--- a/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs
+++ b/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs
@@ -98,6 +98,7 @@ module Cardano.Ledger.Dijkstra.TxBody (
   accountBalanceIntervalsDijkstraTxBodyRawL,
 ) where
 
+import Cardano.Base.Typeable (TypeName (TypeName))
 import Cardano.Ledger.Address (DirectDeposits (..))
 import Cardano.Ledger.Allegra.Scripts (invalidBeforeL, invalidHereAfterL)
 import Cardano.Ledger.Alonzo.TxBody (Indexable (..))
@@ -329,7 +330,7 @@ instance
   where
   decCBOR = withSTxBothLevels @l $ \sTxLevel ->
     decodeSparseKeyed
-      name
+      TypeName
       (requiredFields sTxLevel)
       (pure $ basicDijkstraTxBodyRaw sTxLevel)
       (decoderByKey sTxLevel)
diff --git a/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs b/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
index 87ff8d43441..f8736795eda 100644
--- a/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
+++ b/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
@@ -171,6 +171,7 @@ module Cardano.Ledger.Binary.Decoding.Decoder (
 ) where
 
 import Cardano.Base.IP (IPv4, IPv6, toIPv4w, toIPv6w)
+import Cardano.Base.Typeable (TypeName)
 import Cardano.Ledger.Binary.Plain (
   DecoderError (..),
   cborError,
@@ -1198,7 +1199,7 @@ decodeMapContentsTraverse decodeKey decodeValue =
 decodeSparseKeyed ::
   forall a s.
   -- | Type name used in error messages.
-  String ->
+  TypeName a ->
   -- | Required keys with friendly names per key. After the map is fully
   -- consumed, the absence of any key in this list is reported as a
   -- failure using its name and key.
@@ -1226,7 +1227,7 @@ decodeSparseKeyed name requiredFields initial decoderByKey = do
   pure acc
   where
     failMsg :: String -> Decoder s b
-    failMsg msg = fail $ name <> ":" <> msg
+    failMsg msg = fail $ show name <> ":" <> msg
 
     defLoop :: Set.Set Word -> a -> Int -> Decoder s (Set.Set Word, a)
     defLoop !seen !acc !i
diff --git a/libs/cardano-ledger-core/src/Cardano/Ledger/Core/PParams.hs b/libs/cardano-ledger-core/src/Cardano/Ledger/Core/PParams.hs
index ed2b920964d..74a5b4e482a 100644
--- a/libs/cardano-ledger-core/src/Cardano/Ledger/Core/PParams.hs
+++ b/libs/cardano-ledger-core/src/Cardano/Ledger/Core/PParams.hs
@@ -97,6 +97,7 @@ module Cardano.Ledger.Core.PParams (
   ppuMinFeeBL,
 ) where
 
+import Cardano.Base.Typeable (TypeName (TypeName))
 import Cardano.Ledger.BaseTypes (
   EpochInterval (..),
   KeyValuePairs (..),
@@ -257,7 +258,7 @@ instance EraPParams era => DecCBOR (PParamsUpdate era) where
   decCBOR =
     ifDecoderVersionAtLeast
       (natVersion @12)
-      (decodeSparseKeyed name [] emptyPParamsUpdate decoderByKey)
+      (decodeSparseKeyed TypeName [] emptyPParamsUpdate decoderByKey)
       (decode $ SparseKeyed name emptyPParamsUpdate updateField [])
     where
       name = show . typeRep $ Proxy @(PParamsUpdate era)

From b6277b5afee61f7ba0998e1cda21bf338c7175ba Mon Sep 17 00:00:00 2001
From: Aniket Deshpande <git@aniketd.net>
Date: Thu, 21 May 2026 21:38:51 +0530
Subject: [PATCH 10/13] Replace mapSparseField helpers with decodeAccA.

Migrate AlonzoTxWits and DijkstraTxBody to the new pattern.
---
 .../impl/src/Cardano/Ledger/Alonzo/TxWits.hs  |  25 ++-
 .../src/Cardano/Ledger/Dijkstra/TxBody.hs     | 179 +++++++-----------
 libs/cardano-ledger-binary/CHANGELOG.md       |   2 +-
 .../Cardano/Ledger/Binary/Decoding/Decoder.hs |  87 ++-------
 4 files changed, 104 insertions(+), 189 deletions(-)

diff --git a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs
index 996938fca6f..9086a7067c9 100644
--- a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs
+++ b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxWits.hs
@@ -76,6 +76,7 @@ import Cardano.Ledger.Binary (
   ToCBOR (..),
   TokenType (..),
   allowTag,
+  decodeAccA,
   decodeList,
   decodeListLenOrIndef,
   decodeListLikeWithCount,
@@ -91,8 +92,6 @@ import Cardano.Ledger.Binary (
   ifDecoderVersionAtLeast,
   ifEncodingVersionAtLeast,
   listLenInt,
-  mapSparseField,
-  mapSparseFieldA,
   natVersion,
   peekTokenType,
   setTag,
@@ -626,27 +625,27 @@ instance
         ifDecoderVersionAtLeast (natVersion @12) nonEmptyNoDuplicatesDecoder nonEmptyDecoder
       {-# INLINE addrWitsSetDecoder #-}
 
-      setOrListDecoder :: (Ord a, DecCBOR a) => Decoder s (Set a)
-      setOrListDecoder =
+      setOrListWitsDecoder :: (Ord a, DecCBOR a) => Decoder s (Set a)
+      setOrListWitsDecoder =
         ifDecoderVersionAtLeast
           (natVersion @9)
           addrWitsSetDecoder
           (Set.fromList <$> decodeList decCBOR)
-      {-# INLINE setOrListDecoder #-}
+      {-# INLINE setOrListWitsDecoder #-}
 
       decoderByKey ::
         Annotator (AlonzoTxWitsRaw era) ->
         Word ->
         Maybe (Decoder s (Annotator (AlonzoTxWitsRaw era)))
       decoderByKey acc = \case
-        0 -> Just $ mapSparseField (\x w -> w {atwrAddrTxWits = x}) setOrListDecoder acc
-        1 -> Just $ mapSparseFieldA addScriptsTxWitsRaw nativeScriptsDecoder acc
-        2 -> Just $ mapSparseField (\x w -> w {atwrBootAddrTxWits = x}) setOrListDecoder acc
-        3 -> Just $ mapSparseField addScriptsTxWitsRaw (alonzoPlutusScriptDecoder SPlutusV1) acc
-        4 -> Just $ mapSparseFieldA (\x w -> w {atwrDatsTxWits = x}) decCBOR acc
-        5 -> Just $ mapSparseFieldA (\x w -> w {atwrRdmrsTxWits = x}) decCBOR acc
-        6 -> Just $ mapSparseField addScriptsTxWitsRaw (alonzoPlutusScriptDecoder SPlutusV2) acc
-        7 -> Just $ mapSparseField addScriptsTxWitsRaw (alonzoPlutusScriptDecoder SPlutusV3) acc
+        0 -> Just $ decodeAccA acc (\x w -> w {atwrAddrTxWits = x}) (pure <$> setOrListWitsDecoder)
+        1 -> Just $ decodeAccA acc addScriptsTxWitsRaw nativeScriptsDecoder
+        2 -> Just $ decodeAccA acc (\x w -> w {atwrBootAddrTxWits = x}) (pure <$> setOrListWitsDecoder)
+        3 -> Just $ decodeAccA acc addScriptsTxWitsRaw (pure <$> alonzoPlutusScriptDecoder SPlutusV1)
+        4 -> Just $ decodeAccA acc (\x w -> w {atwrDatsTxWits = x}) decCBOR
+        5 -> Just $ decodeAccA acc (\x w -> w {atwrRdmrsTxWits = x}) decCBOR
+        6 -> Just $ decodeAccA acc addScriptsTxWitsRaw (pure <$> alonzoPlutusScriptDecoder SPlutusV2)
+        7 -> Just $ decodeAccA acc addScriptsTxWitsRaw (pure <$> alonzoPlutusScriptDecoder SPlutusV3)
         _ -> Nothing
       {-# INLINE decoderByKey #-}
 
diff --git a/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs b/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs
index 8ad4dc71659..f1b78f76cef 100644
--- a/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs
+++ b/eras/dijkstra/impl/src/Cardano/Ledger/Dijkstra/TxBody.hs
@@ -146,7 +146,6 @@ import Cardano.Ledger.Val (Val (..))
 import Control.DeepSeq (NFData (..), deepseq)
 import Data.Coerce (coerce)
 import Data.Map.Strict (Map)
-import qualified Data.Map.Strict as Map
 import Data.OMap.Strict (OMap)
 import qualified Data.OMap.Strict as OMap
 import Data.OSet.Strict (OSet, decodeOSet)
@@ -336,152 +335,114 @@ instance
       (decoderByKey sTxLevel)
     where
       name = show . typeRep $ Proxy @(DijkstraTxBodyRaw l era)
+      emptyNamedFailure fieldName requirement =
+        name <> ": " <> emptyFailure fieldName requirement
       decoderByKey ::
         STxBothLevels l era ->
         Annotator (DijkstraTxBodyRaw l era) ->
         Word ->
         Maybe (Decoder s (Annotator (DijkstraTxBodyRaw l era)))
       decoderByKey sTxLevel acc = \case
-        0 -> Just $ mapSparseField (inputsDijkstraTxBodyRawL .~) decCBOR acc
-        1 -> Just $ mapSparseField (outputsDijkstraTxBodyRawL .~) decCBOR acc
-        2 | STopTx <- sTxLevel -> Just $ mapSparseField (feeDijkstraTxBodyRawL .~) decCBOR acc
-        3 -> Just $ mapSparseFieldOptional (vldtDijkstraTxBodyRawL . invalidHereAfterL .~) decCBOR acc
+        0 -> Just $ decodeAccA acc (inputsDijkstraTxBodyRawL .~) (pure <$> decCBOR)
+        1 -> Just $ decodeAccA acc (outputsDijkstraTxBodyRawL .~) (pure <$> decCBOR)
+        2 | STopTx <- sTxLevel -> Just $ decodeAccA acc (feeDijkstraTxBodyRawL .~) (pure <$> decCBOR)
+        3 -> Just $ decodeAccA acc (vldtDijkstraTxBodyRawL . invalidHereAfterL .~) (pure . SJust <$> decCBOR)
         4 ->
           Just $
-            mapSparseFieldGuarded
-              name
-              (emptyFailure "Certificates" "non-empty")
-              OSet.null
-              (certsDijkstraTxBodyRawL .~)
-              decCBOR
-              acc
+            decodeAccA acc (certsDijkstraTxBodyRawL .~) $
+              pure <$> do
+                x <- decCBOR
+                failOnNull x $ emptyNamedFailure "Certificates" "non-empty"
+                pure x
         5 ->
           Just $
-            mapSparseFieldGuarded
-              name
-              (emptyFailure "Withdrawals" "non-empty")
-              (null . unWithdrawals)
-              (withdrawalsDijkstraTxBodyRawL .~)
-              decCBOR
-              acc
-        7 -> Just $ mapSparseFieldOptional (auxDataHashDijkstraTxBodyRawL .~) decCBOR acc
-        8 -> Just $ mapSparseFieldOptional (vldtDijkstraTxBodyRawL . invalidBeforeL .~) decCBOR acc
+            decodeAccA acc (withdrawalsDijkstraTxBodyRawL .~) $
+              pure <$> do
+                x <- decCBOR
+                failOnNull (unWithdrawals x) $ emptyNamedFailure "Withdrawals" "non-empty"
+                pure x
+        7 -> Just $ decodeAccA acc (auxDataHashDijkstraTxBodyRawL .~) (pure . SJust <$> decCBOR)
+        8 -> Just $ decodeAccA acc (vldtDijkstraTxBodyRawL . invalidBeforeL .~) (pure . SJust <$> decCBOR)
         9 ->
           Just $
-            mapSparseFieldGuarded
-              name
-              (emptyFailure "Mint" "non-empty")
-              (== mempty)
-              (mintDijkstraTxBodyRawL .~)
-              decCBOR
-              acc
-        11 -> Just $ mapSparseFieldOptional (scriptIntegrityHashDijkstraTxBodyRawL .~) decCBOR acc
+            decodeAccA acc (mintDijkstraTxBodyRawL .~) $
+              pure <$> do
+                x <- decCBOR
+                failOnMempty x $ emptyNamedFailure "Mint" "non-empty"
+                pure x
+        11 -> Just $ decodeAccA acc (scriptIntegrityHashDijkstraTxBodyRawL .~) (pure . SJust <$> decCBOR)
         13
           | STopTx <- sTxLevel ->
               Just $
-                mapSparseFieldGuarded
-                  name
-                  (emptyFailure "Collateral Inputs" "non-empty")
-                  null
-                  (collateralInputsDijkstraTxBodyRawL .~)
-                  decCBOR
-                  acc
-        -- Keys 14 and 22 are decoded with 'mapSparseField' directly.
-        -- Their lenses target plain values (@'OSet' (Credential Guard)@
-        -- and @'Coin'@), so there's no 'StrictMaybe' to wrap or unwrap.
-        --
-        -- The round-trip stays consistent and symmetric because
-        -- the encoder omits each key when its value equals the
-        -- default, and the decoder's initial accumulator (built by
-        -- 'basicDijkstraTxBodyRaw') starts each field at that same
-        -- default.
-        --
-        -- For example:
-        --   * Key 14 — encoder: @Omit null (Key 14 (To dtbrGuards))@.
-        --   The key is in the serialised bits only when @dtbrGuards@
-        --   is non-empty. The accumulator starts at @mempty@, so a
-        --   missing key keeps the field at @mempty@ — matching what
-        --   the sender skipped.
-        --
-        --   * Key 22 — encoder: @Omit (== mempty) (Key 22 (To
-        --   dtbrTreasuryDonation))@. The key is in the serialised bits
-        --   only when the donation is non-zero. The accumulator starts
-        --   at @mempty@, so a missing key keeps the field at @zero@.
+                decodeAccA acc (collateralInputsDijkstraTxBodyRawL .~) $
+                  pure <$> do
+                    x <- decCBOR
+                    failOnNull x $ emptyNamedFailure "Collateral Inputs" "non-empty"
+                    pure x
         14 ->
-          Just $ mapSparseField (guardsDijkstraTxBodyRawL .~) decodeGuards acc
-        15 -> Just $ mapSparseFieldOptional (networkIdDijkstraTxBodyRawL .~) decCBOR acc
+          -- plain field - initial accumulator already holds the omit-default
+          Just $ decodeAccA acc (guardsDijkstraTxBodyRawL .~) (pure <$> decodeGuards)
+        15 -> Just $ decodeAccA acc (networkIdDijkstraTxBodyRawL .~) (pure . SJust <$> decCBOR)
         16
           | STopTx <- sTxLevel ->
-              Just $ mapSparseFieldOptional (collateralReturnDijkstraTxBodyRawL .~) decCBOR acc
+              Just $ decodeAccA acc (collateralReturnDijkstraTxBodyRawL .~) (pure . SJust <$> decCBOR)
         17
           | STopTx <- sTxLevel ->
-              Just $ mapSparseFieldOptional (totalCollateralDijkstraTxBodyRawL .~) decCBOR acc
+              Just $ decodeAccA acc (totalCollateralDijkstraTxBodyRawL .~) (pure . SJust <$> decCBOR)
         18 ->
           Just $
-            mapSparseFieldGuarded
-              name
-              (emptyFailure "Reference Inputs" "non-empty")
-              null
-              (referenceInputsDijkstraTxBodyRawL .~)
-              decCBOR
-              acc
+            decodeAccA acc (referenceInputsDijkstraTxBodyRawL .~) $
+              pure <$> do
+                x <- decCBOR
+                failOnNull x $ emptyNamedFailure "Reference Inputs" "non-empty"
+                pure x
         19 ->
           Just $
-            mapSparseFieldGuarded
-              name
-              (emptyFailure "VotingProcedures" "non-empty")
-              (null . unVotingProcedures)
-              (votingProceduresDijkstraTxBodyRawL .~)
-              decCBOR
-              acc
+            decodeAccA acc (votingProceduresDijkstraTxBodyRawL .~) $
+              pure <$> do
+                x <- decCBOR
+                failOnNull (unVotingProcedures x) $ emptyNamedFailure "VotingProcedures" "non-empty"
+                pure x
         20 ->
           Just $
-            mapSparseFieldGuarded
-              name
-              (emptyFailure "ProposalProcedures" "non-empty")
-              OSet.null
-              (proposalProceduresDijkstraTxBodyRawL .~)
-              decCBOR
-              acc
-        21 -> Just $ mapSparseFieldOptional (currentTreasuryValueDijkstraTxBodyRawL .~) decCBOR acc
+            decodeAccA acc (proposalProceduresDijkstraTxBodyRawL .~) $
+              pure <$> do
+                x <- decCBOR
+                failOnNull x $ emptyNamedFailure "ProposalProcedures" "non-empty"
+                pure x
+        21 -> Just $ decodeAccA acc (currentTreasuryValueDijkstraTxBodyRawL .~) (pure . SJust <$> decCBOR)
         22 ->
-          -- See comment about field 14.
+          -- plain field - initial accumulator already holds the omit-default
           Just $
-            mapSparseField
-              (treasuryDonationDijkstraTxBodyRawL .~)
-              (decodePositiveCoin $ emptyFailure "Treasury Donation" "non-zero")
+            decodeAccA
               acc
+              (treasuryDonationDijkstraTxBodyRawL .~)
+              (pure <$> decodePositiveCoin (emptyFailure "Treasury Donation" "non-zero"))
         23
           | STopTx <- sTxLevel ->
-              Just $ mapSparseFieldA (subTransactionsDijkstraTxBodyRawL .~) decodeSubTransactions acc
+              Just $ decodeAccA acc (subTransactionsDijkstraTxBodyRawL .~) decodeSubTransactions
         24
           | SSubTx <- sTxLevel ->
               Just $
-                mapSparseFieldGuarded
-                  name
-                  (emptyFailure "RequiredTopLevelGuards" "non-empty")
-                  Map.null
-                  (requiredTopLevelGuardsDijkstraTxBodyRawL .~)
-                  (decodeMap decCBOR (decodeNullStrictMaybe decCBOR))
-                  acc
+                decodeAccA acc (requiredTopLevelGuardsDijkstraTxBodyRawL .~) $
+                  pure <$> do
+                    x <- decodeMap decCBOR (decodeNullStrictMaybe decCBOR)
+                    failOnNull x $ emptyNamedFailure "RequiredTopLevelGuards" "non-empty"
+                    pure x
         25 ->
           Just $
-            mapSparseFieldGuarded
-              name
-              (emptyFailure "DirectDeposits" "non-empty")
-              (null . unDirectDeposits)
-              (directDepositsDijkstraTxBodyRawL .~)
-              decCBOR
-              acc
+            decodeAccA acc (directDepositsDijkstraTxBodyRawL .~) $
+              pure <$> do
+                x <- decCBOR
+                failOnNull (unDirectDeposits x) $ emptyNamedFailure "DirectDeposits" "non-empty"
+                pure x
         26 ->
           Just $
-            mapSparseFieldGuarded
-              name
-              (emptyFailure "AccountBalanceIntervals" "non-empty")
-              (null . unAccountBalanceIntervals)
-              (accountBalanceIntervalsDijkstraTxBodyRawL .~)
-              decCBOR
-              acc
+            decodeAccA acc (accountBalanceIntervalsDijkstraTxBodyRawL .~) $
+              pure <$> do
+                x <- decCBOR
+                failOnNull (unAccountBalanceIntervals x) $ emptyNamedFailure "AccountBalanceIntervals" "non-empty"
+                pure x
         _ -> Nothing
       decodeSubTransactions :: Decoder s (Annotator (OMap TxId (Tx SubTx era)))
       decodeSubTransactions =
diff --git a/libs/cardano-ledger-binary/CHANGELOG.md b/libs/cardano-ledger-binary/CHANGELOG.md
index 49e39839fe1..c8b7a62a2ef 100644
--- a/libs/cardano-ledger-binary/CHANGELOG.md
+++ b/libs/cardano-ledger-binary/CHANGELOG.md
@@ -2,7 +2,7 @@
 
 ## 1.9.0.0
 
-* Add `mapSparseField`, `mapSparseFieldA`, `mapSparseFieldOptional`, `mapSparseFieldGuarded`
+* Add `decodeAccA`, `failOnNull`, `failOnMempty`
 * Add `decodeSparseKeyed`
 * Add `decodeIntegralRational`
 * Add `decodeNonEmptySetLikeEnforceNoDuplicates`
diff --git a/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs b/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
index f8736795eda..cb13445bb7a 100644
--- a/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
+++ b/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
@@ -80,10 +80,9 @@ module Cardano.Ledger.Binary.Decoding.Decoder (
   decodeListLikeEnforceNoDuplicates,
   decodeMapContents,
   decodeSparseKeyed,
-  mapSparseField,
-  mapSparseFieldA,
-  mapSparseFieldOptional,
-  mapSparseFieldGuarded,
+  decodeAccA,
+  failOnNull,
+  failOnMempty,
 
   -- **** Applicaitve
   decodeMapTraverse,
@@ -1257,71 +1256,27 @@ decodeSparseKeyed name requiredFields initial decoderByKey = do
     {-# INLINE step #-}
 {-# INLINE decodeSparseKeyed #-}
 
--- | Decode a value and apply it to a 'Functor'-wrapped accumulator
--- (typically 'Annotator'). Intended for use inside the per-key handler
--- of 'decodeSparseKeyed'.
-mapSparseField ::
-  Functor ann =>
-  -- | Setter that updates the underlying record with the decoded value.
+-- | Decode a value and add it to the accumulator using the
+-- `Applicative` instance.
+decodeAccA ::
+  Applicative f =>
+  -- | Applicative accumulator
+  f t ->
+  -- | Function to adds the decoded value to the accumulator
   (x -> t -> t) ->
-  -- | Decoder for the field value.
-  Decoder s x ->
-  -- | Current accumulator.
-  ann t ->
-  Decoder s (ann t)
-mapSparseField setter dec acc = do
-  !x <- dec
-  pure $ setter x <$> acc
-{-# INLINE mapSparseField #-}
-
--- | Like 'mapSparseField' but the decoder yields an
--- 'Applicative'-wrapped value (e.g. @'Annotator' x@).
-mapSparseFieldA ::
-  Applicative ann =>
-  (x -> t -> t) ->
-  Decoder s (ann x) ->
-  ann t ->
-  Decoder s (ann t)
-mapSparseFieldA setter dec acc = do
+  -- | Decoder of the Applicative value
+  Decoder s (f x) ->
+  Decoder s (f t)
+decodeAccA acc setter dec = do
   !x <- dec
   pure $ setter <$> x <*> acc
-{-# INLINE mapSparseFieldA #-}
-
--- | Like 'mapSparseField' but the setter expects a 'StrictMaybe' value.
--- Useful when the underlying field is a @'Lens'' t ('StrictMaybe' x)@
--- and the key's absence implies 'SNothing' (already set by the initial
--- accumulator).
-mapSparseFieldOptional ::
-  Functor ann =>
-  (StrictMaybe x -> t -> t) ->
-  Decoder s x ->
-  ann t ->
-  Decoder s (ann t)
-mapSparseFieldOptional setter dec acc = do
-  !x <- dec
-  pure $ setter (SJust x) <$> acc
-{-# INLINE mapSparseFieldOptional #-}
-
--- | Like 'mapSparseField' but reject the value when the predicate is
--- satisfied.
-mapSparseFieldGuarded ::
-  Functor ann =>
-  -- | Type name; failure is prefixed with @name:@.
-  String ->
-  -- | Error message used when the predicate rejects the value.
-  String ->
-  -- | Predicate: 'True' means reject.
-  (x -> Bool) ->
-  (x -> t -> t) ->
-  Decoder s x ->
-  ann t ->
-  Decoder s (ann t)
-mapSparseFieldGuarded name msg reject setter dec acc = do
-  !x <- dec
-  if reject x
-    then fail $ name <> ":" <> msg
-    else pure $ setter x <$> acc
-{-# INLINE mapSparseFieldGuarded #-}
+{-# INLINE decodeAccA #-}
+
+failOnNull :: (Foldable f, MonadFail m) => f a -> String -> m ()
+failOnNull f msg = when (null f) $ fail msg
+
+failOnMempty :: (Eq f, Monoid f, MonadFail m) => f -> String -> m ()
+failOnMempty f msg = when (f == mempty) $ fail msg
 
 --------------------------------------------------------------------------------
 -- Time

From 4d13e21e6287f4a76c9230fc6714313df82b7404 Mon Sep 17 00:00:00 2001
From: Aniket Deshpande <git@aniketd.mailer.me>
Date: Fri, 22 May 2026 13:28:57 +0530
Subject: [PATCH 11/13] Fix TypeName in failing test

---
 .../impl/testlib/Test/Cardano/Ledger/Alonzo/Binary/Golden.hs    | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/eras/alonzo/impl/testlib/Test/Cardano/Ledger/Alonzo/Binary/Golden.hs b/eras/alonzo/impl/testlib/Test/Cardano/Ledger/Alonzo/Binary/Golden.hs
index 55ecb67b60d..6e52c34b0da 100644
--- a/eras/alonzo/impl/testlib/Test/Cardano/Ledger/Alonzo/Binary/Golden.hs
+++ b/eras/alonzo/impl/testlib/Test/Cardano/Ledger/Alonzo/Binary/Golden.hs
@@ -88,7 +88,7 @@ txWitsDecodingFailsOnInvalidField version validFields =
           DecoderErrorDeserialiseFailure lbl (DeserialiseFailure 1 "expected word")
   where
     lbl = Binary.label $ Proxy @(Annotator (TxWits era))
-    typeName = show (typeRep (Proxy @(AlonzoTxWitsRaw era)))
+    typeName = show (typeRep (Proxy @(Annotator (AlonzoTxWitsRaw era))))
 
 spec ::
   forall era.

From d31f9552f273717a37d6e2d63cf043628886ca4f Mon Sep 17 00:00:00 2001
From: Aniket Deshpande <git@aniketd.net>
Date: Mon, 25 May 2026 16:27:24 +0530
Subject: [PATCH 12/13] Remove SRP; update index-state

---
 cabal.project | 9 +--------
 flake.lock    | 6 +++---
 2 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/cabal.project b/cabal.project
index a23063d9905..deb7b5dfc67 100644
--- a/cabal.project
+++ b/cabal.project
@@ -10,13 +10,6 @@ repository cardano-haskell-packages
     c00aae8461a256275598500ea0e187588c35a5d5d7454fb57eac18d9edb86a56
     d4a35cd3121aa00d18544bb0ac01c3e1691d618f462c46129271bccf39f7e8ee
 
-source-repository-package
-  type: git
-  location: https://github.com/IntersectMBO/cardano-base.git
-  subdir: cardano-base
-  --sha256: sha256-Gj8BPEew+UYkCWr3D0LgA6dvhYof49V20XRMRMf1FzY=
-  tag: efe33cb3739f5c90b733b730bdeffa11a75f291d
-
 source-repository-package
   type: git
   location: https://github.com/IntersectMBO/formal-ledger-specifications.git
@@ -35,7 +28,7 @@ source-repository-package
 -- see CONTRIBUTING.md#to-update-the-referenced-agda-ledger-spec
 index-state:
   , hackage.haskell.org 2026-05-06T14:09:41Z
-  , cardano-haskell-packages 2026-04-11T06:29:42Z
+  , cardano-haskell-packages 2026-05-22T05:43:37Z
 
 packages:
   -- == Byron era ==
diff --git a/flake.lock b/flake.lock
index 2741b7d461f..2b204fd3c27 100644
--- a/flake.lock
+++ b/flake.lock
@@ -3,11 +3,11 @@
     "CHaP": {
       "flake": false,
       "locked": {
-        "lastModified": 1775892872,
-        "narHash": "sha256-8qwpclExAZYF5e35xqt9yQYcal3FJLirKNIMiomAIvs=",
+        "lastModified": 1779431600,
+        "narHash": "sha256-BveisGfAV1GBrwP83S5w0D7B1t3VPaoHGGlRcnHYN5E=",
         "owner": "intersectmbo",
         "repo": "cardano-haskell-packages",
-        "rev": "86660ad10909f521a9c42cb01e9626aefd3903cf",
+        "rev": "8479db771a3186eb326e42d8480eddc20a208275",
         "type": "github"
       },
       "original": {

From 7026d3748e930eba568d9ec8d9860b1cec7c7e86 Mon Sep 17 00:00:00 2001
From: Aniket Deshpande <git@aniketd.net>
Date: Mon, 25 May 2026 16:27:44 +0530
Subject: [PATCH 13/13] Rm redundant argument; add spaces in error reports

---
 .../impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs      | 12 ++++++------
 .../Test/Cardano/Ledger/Alonzo/Binary/Golden.hs      |  2 +-
 .../src/Cardano/Ledger/Binary/Decoding/Decoder.hs    |  2 +-
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
index 981a2e7ef3b..f84e6ec929b 100644
--- a/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
+++ b/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/TxAuxData.hs
@@ -260,16 +260,16 @@ instance
             (\scripts ad -> ad {atadrNativeScripts = atadrNativeScripts ad <> scripts})
               <$> x
               <*> acc
-        2 -> decodeAddPlutus PlutusV1 acc
-        3 -> decodeAddPlutus PlutusV2 acc
-        4 -> decodeAddPlutus PlutusV3 acc
-        5 -> decodeAddPlutus PlutusV4 acc
+        2 -> decodeAddPlutus PlutusV1
+        3 -> decodeAddPlutus PlutusV2
+        4 -> decodeAddPlutus PlutusV3
+        5 -> decodeAddPlutus PlutusV4
         _ -> Nothing
         where
-          decodeAddPlutus lang accu = Just $ do
+          decodeAddPlutus lang = Just $ do
             guardPlutus lang
             !x <- decCBOR
-            pure $ addPlutusScripts lang x <$> accu
+            pure $ addPlutusScripts lang x <$> acc
           {-# INLINE decodeAddPlutus #-}
       {-# INLINE decoderByKey #-}
 
diff --git a/eras/alonzo/impl/testlib/Test/Cardano/Ledger/Alonzo/Binary/Golden.hs b/eras/alonzo/impl/testlib/Test/Cardano/Ledger/Alonzo/Binary/Golden.hs
index 6e52c34b0da..2a9f572c6c2 100644
--- a/eras/alonzo/impl/testlib/Test/Cardano/Ledger/Alonzo/Binary/Golden.hs
+++ b/eras/alonzo/impl/testlib/Test/Cardano/Ledger/Alonzo/Binary/Golden.hs
@@ -80,7 +80,7 @@ txWitsDecodingFailsOnInvalidField version validFields =
             lbl
             ( DeserialiseFailure (if n >= 24 then 3 else 2) $
                 if version >= natVersion @12
-                  then typeName <> ":Unknown field key " <> show n
+                  then typeName <> ": Unknown field key " <> show n
                   -- TODO fix the `occured` typo in the produced value
                   else "An error occured while decoding (Int,Void) not a valid key:.\nError: " <> show n
             )
diff --git a/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs b/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
index cb13445bb7a..207186ad197 100644
--- a/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
+++ b/libs/cardano-ledger-binary/src/Cardano/Ledger/Binary/Decoding/Decoder.hs
@@ -1216,7 +1216,7 @@ decodeSparseKeyed name requiredFields initial decoderByKey = do
       Just len -> defLoop Set.empty initial len
       Nothing -> indefLoop Set.empty initial
   let missing =
-        [ show n <> ":" <> show k
+        [ show n <> ": " <> show k
         | (k, n) <- requiredFields
         , not $ Set.member k seen
         ]