pallas-txbuilder: thread certificates through StagingTransaction → Conway build

second of the upstream TODOs. addresses the `// pub certificates: TODO`
comment in transaction/model.rs and the `certificates: None, // TODO`
in conway.rs:243.

implementation:
- new field: pub certificates: Option<Vec<Vec<u8>>> on StagingTransaction.
  cbor bytes per cert (each entry is conway::Certificate) — same opaque-
  bytes pattern as auxiliary_data, for the same reason (Certificate
  doesn't impl Eq).
- builder: .add_certificate(cbor_bytes) and .clear_certificates().
- conway::build_conway_raw decodes each entry via
  Certificate::decode_fragment + plumbs into TransactionBody.certificates
  via NonEmptySet::from_vec. fragment-decode failures map to
  TxBuilderError::CorruptedTxBytes (same as aux_data path).

tests:
- certificates_plumb_through_to_tx_body: encodes a
  StakeRegistration(AddrKeyhash([7;28])), attaches, builds, decodes
  resulting tx, asserts the cert round-trips byte-for-byte.
- no_certificates_means_none: confirms unset path keeps
  body.certificates None (no spurious empty Set).

unblocks aldabra phase 4.6 stake delegation. PR upstream still pending;
this is part of the same vendored fork as the auxiliary_data work.

pallas-txbuilder/src/conway.rs

@@ -4,10 +4,10 @@ use pallas_codec::utils::CborWrap;
 use pallas_crypto::hash::Hash;
 use pallas_primitives::{
     conway::{
-        AuxiliaryData, DatumOption, ExUnits as PallasExUnits, NativeScript, NetworkId, NonZeroInt,
-        PlutusData, PlutusScript, PostAlonzoTransactionOutput, PseudoScript as PallasScript,
-        PseudoTransactionOutput, Redeemer, RedeemerTag, TransactionBody, TransactionInput, Tx,
-        Value, WitnessSet,
+        AuxiliaryData, Certificate, DatumOption, ExUnits as PallasExUnits, NativeScript, NetworkId,
+        NonZeroInt, PlutusData, PlutusScript, PostAlonzoTransactionOutput,
+        PseudoScript as PallasScript, PseudoTransactionOutput, Redeemer, RedeemerTag,
+        TransactionBody, TransactionInput, Tx, Value, WitnessSet,
     },
     Fragment, NonEmptyKeyValuePairs, NonEmptySet, PositiveCoin,
 };
@@ -240,8 +240,18 @@ impl BuildConway for StagingTransaction {
                 ttl: self.invalid_from_slot,
                 validity_interval_start: self.valid_from_slot,
                 fee: self.fee.unwrap_or_default(),
-                certificates: None,        // TODO
-                withdrawals: None,         // TODO
+                certificates: NonEmptySet::from_vec(
+                    self.certificates
+                        .as_deref()
+                        .unwrap_or(&[])
+                        .iter()
+                        .map(|bytes| {
+                            Certificate::decode_fragment(bytes)
+                                .map_err(|_| TxBuilderError::CorruptedTxBytes)
+                        })
+                        .collect::<Result<Vec<_>, _>>()?,
+                ),
+                withdrawals: None, // TODO
                 auxiliary_data_hash: None, // TODO (accept user input)
                 mint,
                 script_data_hash,
@@ -439,6 +449,51 @@ mod tests {
         assert_eq!(round_tripped_bytes, original_again);
     }
 
+    #[test]
+    fn certificates_plumb_through_to_tx_body() {
+        use pallas_primitives::conway::{Certificate, StakeCredential};
+        use pallas_crypto::hash::Hash;
+
+        // A trivial stake-registration cert.
+        let stake_pkh = Hash::<28>::from([7u8; 28]);
+        let cert = Certificate::StakeRegistration(StakeCredential::AddrKeyhash(stake_pkh));
+        let cert_bytes = minicbor::to_vec(&cert).expect("encode cert");
+
+        let tx = StagingTransaction::new()
+            .add_certificate(cert_bytes)
+            .network_id(0)
+            .fee(180_000)
+            .build_conway_raw()
+            .expect("build_conway_raw");
+
+        let body = pallas_primitives::conway::Tx::decode_fragment(tx.tx_bytes.as_ref())
+            .expect("decode tx_bytes");
+        let certs = body
+            .transaction_body
+            .certificates
+            .expect("certificates field populated");
+        let certs_vec: Vec<_> = certs.to_vec();
+        assert_eq!(certs_vec.len(), 1);
+        match &certs_vec[0] {
+            Certificate::StakeRegistration(StakeCredential::AddrKeyhash(h)) => {
+                assert_eq!(h.as_ref(), &[7u8; 28]);
+            }
+            other => panic!("expected StakeRegistration, got {other:?}"),
+        }
+    }
+
+    #[test]
+    fn no_certificates_means_none() {
+        let tx = StagingTransaction::new()
+            .network_id(0)
+            .fee(180_000)
+            .build_conway_raw()
+            .expect("build_conway_raw");
+        let body = pallas_primitives::conway::Tx::decode_fragment(tx.tx_bytes.as_ref())
+            .expect("decode tx_bytes");
+        assert!(body.transaction_body.certificates.is_none());
+    }
+
     #[test]
     fn no_auxiliary_data_means_no_hash() {
         let tx = StagingTransaction::new()

pallas-txbuilder/src/transaction/model.rs

@@ -45,7 +45,11 @@ pub struct StagingTransaction {
     /// doesn't implement `Eq`, which the rest of this struct requires.
     /// `conway::build_conway_raw` decodes on the way out.
     pub auxiliary_data: Option<Vec<u8>>,
-    // pub certificates: TODO
+    /// CBOR-encoded `pallas_primitives::conway::Certificate` entries,
+    /// in tx order. `conway::build_conway_raw` decodes each one and
+    /// plumbs them into `TransactionBody.certificates`. Used for
+    /// stake registration/delegation, pool registration, DRep ops, etc.
+    pub certificates: Option<Vec<Vec<u8>>>,
     // pub withdrawals: TODO
     // pub updates: TODO
     // pub phase_2_valid: TODO
@@ -396,6 +400,26 @@ impl StagingTransaction {
         self.auxiliary_data = None;
         self
     }
+
+    /// Append a CBOR-encoded `conway::Certificate` to the tx body.
+    /// Common cases: stake registration, stake delegation, DRep
+    /// registration, pool retirement.
+    ///
+    /// Encode the typed `Certificate` via
+    /// `pallas_codec::minicbor::to_vec(&cert)` or
+    /// `Fragment::encode_fragment` and pass the bytes here.
+    pub fn add_certificate(mut self, cbor_bytes: Vec<u8>) -> Self {
+        let mut certs = self.certificates.unwrap_or_default();
+        certs.push(cbor_bytes);
+        self.certificates = Some(certs);
+        self
+    }
+
+    /// Drop any certificates previously attached.
+    pub fn clear_certificates(mut self) -> Self {
+        self.certificates = None;
+        self
+    }
 }
 
 // TODO: Don't want our wrapper types in fields public

pallas-txbuilder/src/transaction/serialise.rs

@@ -481,6 +481,7 @@ mod tests {
             script_data_hash: Some(Bytes32([0; 32])),
             language_view: Some(crate::scriptdata::LanguageView(1, vec![1, 2, 3])),
             auxiliary_data: None,
+            certificates: None,
         };
 
         let serialised_tx = serde_json::to_string(&tx).unwrap();