refactor(zcash): use shielded pool display directly

diff --git a/rust/apps/zcash/src/pczt/check.rs b/rust/apps/zcash/src/pczt/check.rs
index b67aa4d..f3873fd 100644
--- a/rust/apps/zcash/src/pczt/check.rs
+++ b/rust/apps/zcash/src/pczt/check.rs
@@ -396,7 +396,6 @@ fn check_shielded_bundle<P: consensus::Parameters>(
     bundle: &orchard::pczt::Bundle,
     pool: ShieldedPool,
 ) -> Result<(), ZcashError> {
-    let pool_label = pool;
     let fvk = ufvk.orchard().ok_or(ZcashError::InvalidDataError(
         "orchard fvk is not present".to_string(),
     ))?;
@@ -427,7 +426,7 @@ fn check_shielded_bundle<P: consensus::Parameters>(
     match calculated_value_balance {
         Ok(value_balance) if &value_balance == bundle.value_sum() => Ok(()),
         _ => Err(ZcashError::InvalidPczt(format!(
-            "invalid {pool_label} bundle value balance"
+            "invalid {pool} bundle value balance"
         ))),
     }
 }
@@ -446,7 +445,6 @@ 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;
     let fvk = ufvk.orchard().ok_or(ZcashError::InvalidDataError(
         "orchard fvk is not present".to_string(),
     ))?;
@@ -520,7 +518,7 @@ fn check_and_parse_shielded_bundle<P: consensus::Parameters>(
             }
         }
         _ => Err(ZcashError::InvalidPczt(format!(
-            "invalid {pool_label} bundle value balance"
+            "invalid {pool} bundle value balance"
         ))),
     }
 }
@@ -537,12 +535,11 @@ fn check_action<P: consensus::Parameters>(
     flags: &orchard::bundle::Flags,
     pool: ShieldedPool,
 ) -> Result<ParsedTo, ZcashError> {
-    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| {
-        ZcashError::InvalidPczt(format!("invalid cv_net in {pool_label} action: {e:?}"))
-    })?;
+    action
+        .verify_cv_net()
+        .map_err(|e| ZcashError::InvalidPczt(format!("invalid cv_net in {pool} action: {e:?}")))?;
 
     check_action_spend(
         params,
@@ -565,7 +562,6 @@ fn check_action_spend<P: consensus::Parameters>(
     spend: &orchard::pczt::Spend,
     pool: ShieldedPool,
 ) -> Result<(), ZcashError> {
-    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(
@@ -604,11 +600,11 @@ fn check_action_spend<P: consensus::Parameters>(
 
     if let Some(expected_fvk) = can_verify_nf_rk {
         spend.verify_nullifier(expected_fvk).map_err(|e| {
-            ZcashError::InvalidPczt(format!("invalid {pool_label} action nullifier: {e:?}"))
-        })?;
-        spend.verify_rk(expected_fvk).map_err(|e| {
-            ZcashError::InvalidPczt(format!("invalid {pool_label} action rk: {e:?}"))
+            ZcashError::InvalidPczt(format!("invalid {pool} action nullifier: {e:?}"))
         })?;
+        spend
+            .verify_rk(expected_fvk)
+            .map_err(|e| ZcashError::InvalidPczt(format!("invalid {pool} action rk: {e:?}")))?;
     }
 
     Ok(())
@@ -622,11 +618,10 @@ fn check_action_output<P: consensus::Parameters>(
     flags: &orchard::bundle::Flags,
     pool: ShieldedPool,
 ) -> Result<ParsedTo, ZcashError> {
-    let pool_label = pool;
     action
         .output()
         .verify_note_commitment(action.spend())
-        .map_err(|e| ZcashError::InvalidPczt(format!("invalid {pool_label} action cmx: {e:?}")))?;
+        .map_err(|e| ZcashError::InvalidPczt(format!("invalid {pool} action cmx: {e:?}")))?;
 
     // Decode and validate the recipient, rejecting non-zero outputs the device cannot review.
     let parsed_to = super::parse::parse_orchard_output(params, keys, action, pool)?;
diff --git a/rust/apps/zcash/src/pczt/mod.rs b/rust/apps/zcash/src/pczt/mod.rs
index 6a1db8f..1bc27f7 100644
--- a/rust/apps/zcash/src/pczt/mod.rs
+++ b/rust/apps/zcash/src/pczt/mod.rs
@@ -202,7 +202,6 @@ 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;
     let Some((derivation_seed_fingerprint, derivation_path)) = derivation else {
         return Ok(None);
     };
@@ -212,7 +211,7 @@ pub(crate) fn matching_seed_supported_orchard_account_parts(
 
     let unsupported_path = || {
         crate::errors::ZcashError::InvalidPczt(alloc::format!(
-            "unsupported {pool_label} spend ZIP 32 derivation path"
+            "unsupported {pool} spend ZIP 32 derivation path"
         ))
     };
 
diff --git a/rust/apps/zcash/src/pczt/parse.rs b/rust/apps/zcash/src/pczt/parse.rs
index 2a24259..0f218d7 100644
--- a/rust/apps/zcash/src/pczt/parse.rs
+++ b/rust/apps/zcash/src/pczt/parse.rs
@@ -191,21 +191,19 @@ 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;
-
         let recipient = action.output().recipient().ok_or_else(|| {
-            ZcashError::InvalidPczt(format!("Missing recipient field for {pool_label} action"))
+            ZcashError::InvalidPczt(format!("Missing recipient field for {pool} action"))
         })?;
         let value = action.output().value().ok_or_else(|| {
-            ZcashError::InvalidPczt(format!("Missing value field for {pool_label} action"))
+            ZcashError::InvalidPczt(format!("Missing value field for {pool} action"))
         })?;
         let rho = orchard::note::Rho::from_bytes(&action.spend().nullifier().to_bytes())
             .into_option()
             .ok_or_else(|| {
-                ZcashError::InvalidPczt(format!("Missing rho field for {pool_label} action"))
+                ZcashError::InvalidPczt(format!("Missing rho field for {pool} action"))
             })?;
         let rseed = action.output().rseed().ok_or_else(|| {
-            ZcashError::InvalidPczt(format!("Missing rseed field for {pool_label} action"))
+            ZcashError::InvalidPczt(format!("Missing rseed field for {pool} action"))
         })?;
 
         let note = orchard::Note::from_parts(
@@ -216,9 +214,7 @@ pub(crate) fn decode_output_enc_ciphertext(
             (*action.output().note_version()).into(),
         )
         .into_option()
-        .ok_or_else(|| {
-            ZcashError::InvalidPczt(format!("{pool_label} action contains invalid note"))
-        })?;
+        .ok_or_else(|| ZcashError::InvalidPczt(format!("{pool} action contains invalid note")))?;
 
         Ok(match pool {
             ShieldedPool::Orchard => {
@@ -705,7 +701,6 @@ pub(crate) fn parse_orchard_output<P: consensus::Parameters>(
     action: &orchard::pczt::Action,
     pool: ShieldedPool,
 ) -> Result<ParsedTo, ZcashError> {
-    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
@@ -745,7 +740,7 @@ pub(crate) fn parse_orchard_output<P: consensus::Parameters>(
                 let belongs_to_wallet = is_external || is_internal;
                 if is_internal_ovk && !belongs_to_wallet {
                     return Err(ZcashError::InvalidPczt(alloc::format!(
-                        "{pool_label} output was recoverable with an internal OVK but does not belong to this wallet"
+                        "{pool} output was recoverable with an internal OVK but does not belong to this wallet"
                     )));
                 }
                 let is_dummy = match vk {
@@ -774,7 +769,7 @@ pub(crate) fn parse_orchard_output<P: consensus::Parameters>(
                 // `vk.is_none()` as a fallback. We require that non-trivial outputs are
                 // visible to the Keystone device.
                 (None, Some(value)) if value.inner() != 0 => Err(ZcashError::InvalidPczt(
-                    alloc::format!("enc_ciphertext field for {pool_label} action is undecryptable"),
+                    alloc::format!("enc_ciphertext field for {pool} action is undecryptable"),
                 )),
                 // We couldn't directly decrypt a zero-valued note. This is okay because
                 // it is checked elsewhere that the direct details in the PCZT are valid,
@@ -829,7 +824,7 @@ pub(crate) fn parse_orchard_output<P: consensus::Parameters>(
                 }
                 (None, 0) => Ok(("Dummy output".into(), true)),
                 (None, _) => Err(ZcashError::InvalidPczt(alloc::format!(
-                    "missing user address for {pool_label} output"
+                    "missing user address for {pool} output"
                 ))),
             }?;
             Ok(ParsedTo::new(
diff --git a/rust/apps/zcash/src/pczt/sign.rs b/rust/apps/zcash/src/pczt/sign.rs
index 1d49260..5ed0e79 100644
--- a/rust/apps/zcash/src/pczt/sign.rs
+++ b/rust/apps/zcash/src/pczt/sign.rs
@@ -324,7 +324,6 @@ 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;
         if action.spend().spend_auth_sig().is_some() {
             return Ok(());
         }
@@ -333,7 +332,8 @@ impl PcztSigner for SeedSigner<'_> {
                 Some(0) | None => return Ok(()),
                 Some(_) => {
                     return Err(ZcashError::InvalidPczt(format!(
-                        "{pool_label} spend dummy_sk is only valid for dummy spends"
+                        "{} spend dummy_sk is only valid for dummy spends",
+                        self.pool
                     )));
                 }
             }
@@ -375,7 +375,7 @@ impl PcztSigner for SeedSigner<'_> {
                     OsRng,
                 )
                 .map_err(|e| {
-                    ZcashError::SigningError(format!("failed to sign {pool_label} action: {e:?}"))
+                    ZcashError::SigningError(format!("failed to sign {} action: {e:?}", self.pool))
                 })
         })?;
         self.signed.set(self.signed.get() + 1);