refactor(zcash): display shielded pool names

diff --git a/rust/apps/zcash/src/pczt/check.rs b/rust/apps/zcash/src/pczt/check.rs
index 7acd520..ca9d8f7 100644
--- a/rust/apps/zcash/src/pczt/check.rs
+++ b/rust/apps/zcash/src/pczt/check.rs
@@ -396,7 +396,7 @@ fn check_shielded_bundle<P: consensus::Parameters>(
     bundle: &orchard::pczt::Bundle,
     pool: ShieldedPool,
 ) -> Result<(), ZcashError> {
-    let pool_label = pool.label();
+    let pool_label = pool;
     let fvk = ufvk.orchard().ok_or(ZcashError::InvalidDataError(
         "orchard fvk is not present".to_string(),
     ))?;
@@ -446,7 +446,7 @@ fn check_and_parse_shielded_bundle<P: consensus::Parameters>(
     pool: ShieldedPool,
     checked_actions: &mut alloc::vec::Vec<ShieldedAction>,
 ) -> Result<Option<ParsedOrchard>, ZcashError> {
-    let pool_label = pool.label();
+    let pool_label = pool;
     let fvk = ufvk.orchard().ok_or(ZcashError::InvalidDataError(
         "orchard fvk is not present".to_string(),
     ))?;
@@ -537,7 +537,7 @@ fn check_action<P: consensus::Parameters>(
     flags: &orchard::bundle::Flags,
     pool: ShieldedPool,
 ) -> Result<ParsedTo, ZcashError> {
-    let pool_label = pool.label();
+    let pool_label = pool;
     // Check `cv_net` first so we know that the `value` fields for both the spend and the
     // output are present and correct.
     action.verify_cv_net().map_err(|e| {
@@ -565,7 +565,7 @@ fn check_action_spend<P: consensus::Parameters>(
     spend: &orchard::pczt::Spend,
     pool: ShieldedPool,
 ) -> Result<(), ZcashError> {
-    let pool_label = pool.label();
+    let pool_label = pool;
     if let (Some(value), Some(zip32_derivation)) = (spend.value(), spend.zip32_derivation()) {
         if value.inner() != 0 && zip32_derivation.seed_fingerprint() == seed_fingerprint {
             let matched_account = super::matching_seed_supported_orchard_account(
@@ -622,7 +622,7 @@ fn check_action_output<P: consensus::Parameters>(
     flags: &orchard::bundle::Flags,
     pool: ShieldedPool,
 ) -> Result<ParsedTo, ZcashError> {
-    let pool_label = pool.label();
+    let pool_label = pool;
     action
         .output()
         .verify_note_commitment(action.spend())
@@ -651,15 +651,12 @@ fn check_restricted_zero_value_output(
     }
 
     let recipient = action.output().recipient().ok_or_else(|| {
-        ZcashError::InvalidPczt(format!(
-            "missing recipient for funded {} output",
-            pool.label()
-        ))
+        ZcashError::InvalidPczt(format!("missing recipient for funded {} output", pool))
     })?;
     if !super::parse::is_wallet_orchard_address(keys, &recipient)? {
         return Err(ZcashError::InvalidPczt(format!(
             "funded {} output paired with a zero-value spend does not belong to the selected account",
-            pool.label()
+            pool
         )));
     }
 
diff --git a/rust/apps/zcash/src/pczt/mod.rs b/rust/apps/zcash/src/pczt/mod.rs
index 30fb485..5e236b2 100644
--- a/rust/apps/zcash/src/pczt/mod.rs
+++ b/rust/apps/zcash/src/pczt/mod.rs
@@ -146,11 +146,11 @@ pub(crate) enum ShieldedPool {
 }
 
 #[cfg(feature = "cypherpunk")]
-impl ShieldedPool {
-    pub(crate) fn label(self) -> &'static str {
+impl core::fmt::Display for ShieldedPool {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         match self {
-            ShieldedPool::Orchard => "Orchard",
-            ShieldedPool::Ironwood => "Ironwood",
+            ShieldedPool::Orchard => f.write_str("Orchard"),
+            ShieldedPool::Ironwood => f.write_str("Ironwood"),
         }
     }
 }
@@ -189,7 +189,7 @@ pub(crate) fn matching_seed_supported_orchard_account_parts(
     coin_type: u32,
     pool: ShieldedPool,
 ) -> Result<Option<zcash_vendor::zip32::AccountId>, crate::errors::ZcashError> {
-    let pool_label = pool.label();
+    let pool_label = pool;
     let Some((derivation_seed_fingerprint, derivation_path)) = derivation else {
         return Ok(None);
     };
diff --git a/rust/apps/zcash/src/pczt/parse.rs b/rust/apps/zcash/src/pczt/parse.rs
index 1eef6b1..26d87d0 100644
--- a/rust/apps/zcash/src/pczt/parse.rs
+++ b/rust/apps/zcash/src/pczt/parse.rs
@@ -191,7 +191,7 @@ pub(crate) fn decode_output_enc_ciphertext(
         })
     } else {
         // If we reached here, none of our OVKs matched; recover directly as the fallback.
-        let pool_label = pool.label();
+        let pool_label = pool;
 
         let recipient = action.output().recipient().ok_or_else(|| {
             ZcashError::InvalidPczt(format!("Missing recipient field for {pool_label} action"))
@@ -705,7 +705,7 @@ pub(crate) fn parse_orchard_output<P: consensus::Parameters>(
     action: &orchard::pczt::Action,
     pool: ShieldedPool,
 ) -> Result<ParsedTo, ZcashError> {
-    let pool_label = pool.label();
+    let pool_label = pool;
     let output = action.output();
 
     // we should verify the cv_net in checking phrase, the transaction checking should failed if the net value is not correct
diff --git a/rust/apps/zcash/src/pczt/sign.rs b/rust/apps/zcash/src/pczt/sign.rs
index ec079b5..023c862 100644
--- a/rust/apps/zcash/src/pczt/sign.rs
+++ b/rust/apps/zcash/src/pczt/sign.rs
@@ -256,7 +256,7 @@ impl<'a> SeedSigner<'a> {
                 |e| {
                     ZcashError::SigningError(format!(
                         "failed to derive {} spending key: {e:?}",
-                        self.pool.label()
+                        self.pool
                     ))
                 },
             )?,
@@ -324,7 +324,7 @@ impl PcztSigner for SeedSigner<'_> {
         // Strict per-action validation, ported verbatim from the previous
         // collect_orchard_bundle_signing_keys so the lean signer keeps identical
         // skip/reject semantics to the RoleSigner path.
-        let pool_label = self.pool.label();
+        let pool_label = self.pool;
         if action.spend().spend_auth_sig().is_some() {
             return Ok(());
         }