refactor: thread ShieldedPool enum instead of stringly pool labels

diff --git a/rust/apps/zcash/src/pczt/check.rs b/rust/apps/zcash/src/pczt/check.rs
index c722867..77051fc 100644
--- a/rust/apps/zcash/src/pczt/check.rs
+++ b/rust/apps/zcash/src/pczt/check.rs
@@ -23,6 +23,9 @@ use zcash_vendor::{
 #[cfg(feature = "cypherpunk")]
 use zcash_vendor::zcash_protocol::consensus::NetworkConstants;
 
+#[cfg(feature = "cypherpunk")]
+use super::ShieldedPool;
+
 #[cfg(feature = "cypherpunk")]
 fn map_orchard_verifier_error(
     error: pczt::roles::verifier::OrchardError<ZcashError>,
@@ -46,13 +49,13 @@ pub fn check_pczt_orchard<P: consensus::Parameters>(
     let should_process_ironwood = super::pczt_should_process_ironwood(pczt);
     let verifier = Verifier::new(pczt.clone())
         .with_orchard(|bundle| {
-            check_orchard(
+            check_shielded_bundle(
                 params,
                 seed_fingerprint,
                 account_index,
                 ufvk,
                 bundle,
-                "Orchard",
+                ShieldedPool::Orchard,
             )
             .map_err(pczt::roles::verifier::OrchardError::Custom)?;
             Ok(())
@@ -62,13 +65,13 @@ pub fn check_pczt_orchard<P: consensus::Parameters>(
     if should_process_ironwood {
         verifier
             .with_ironwood(|bundle| {
-                check_orchard(
+                check_shielded_bundle(
                     params,
                     seed_fingerprint,
                     account_index,
                     ufvk,
                     bundle,
-                    "Ironwood",
+                    ShieldedPool::Ironwood,
                 )
                 .map_err(pczt::roles::verifier::OrchardError::Custom)?;
                 Ok(())
@@ -294,14 +297,15 @@ fn check_transparent_output<P: consensus::Parameters>(
 
 #[cfg(feature = "cypherpunk")]
 // check orchard bundle
-fn check_orchard<P: consensus::Parameters>(
+fn check_shielded_bundle<P: consensus::Parameters>(
     params: &P,
     seed_fingerprint: &[u8; 32],
     account_index: zip32::AccountId,
     ufvk: &UnifiedFullViewingKey,
     bundle: &orchard::pczt::Bundle,
-    pool_label: &str,
+    pool: ShieldedPool,
 ) -> Result<(), ZcashError> {
+    let pool_label = pool.label();
     bundle.actions().iter().try_for_each(|action| {
         check_action(
             params,
@@ -309,7 +313,7 @@ fn check_orchard<P: consensus::Parameters>(
             account_index,
             ufvk,
             action,
-            pool_label,
+            pool,
         )?;
         Ok::<_, ZcashError>(())
     })?;
@@ -340,8 +344,9 @@ fn check_action<P: consensus::Parameters>(
     account_index: zip32::AccountId,
     ufvk: &UnifiedFullViewingKey,
     action: &orchard::pczt::Action,
-    pool_label: &str,
+    pool: ShieldedPool,
 ) -> Result<(), ZcashError> {
+    let pool_label = pool.label();
     // 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| {
@@ -359,9 +364,9 @@ fn check_action<P: consensus::Parameters>(
         account_index,
         fvk,
         action.spend(),
-        pool_label,
+        pool,
     )?;
-    check_action_output(params, ufvk, action, pool_label)?;
+    check_action_output(params, ufvk, action, pool)?;
     Ok(())
 }
 
@@ -373,8 +378,9 @@ fn check_action_spend<P: consensus::Parameters>(
     account_index: zip32::AccountId,
     fvk: &FullViewingKey,
     spend: &orchard::pczt::Spend,
-    pool_label: &str,
+    pool: ShieldedPool,
 ) -> Result<(), ZcashError> {
+    let pool_label = pool.label();
     // We can only verify the `nullifier` and `rk` fields of a spend if we know its FVK.
     let can_verify_nf_rk = match (spend.value(), spend.fvk(), spend.zip32_derivation()) {
         // Dummy notes use randomly-generated FVKs, so if one is already present then
@@ -426,8 +432,9 @@ fn check_action_output<P: consensus::Parameters>(
     params: &P,
     ufvk: &UnifiedFullViewingKey,
     action: &orchard::pczt::Action,
-    pool_label: &str,
+    pool: ShieldedPool,
 ) -> Result<(), ZcashError> {
+    let pool_label = pool.label();
     action
         .output()
         .verify_note_commitment(action.spend())
diff --git a/rust/apps/zcash/src/pczt/mod.rs b/rust/apps/zcash/src/pczt/mod.rs
index 31304fa..33f655d 100644
--- a/rust/apps/zcash/src/pczt/mod.rs
+++ b/rust/apps/zcash/src/pczt/mod.rs
@@ -100,6 +100,28 @@ pub(crate) fn transparent_derivation_matches_selected_account<
     Ok(true)
 }
 
+/// Which shielded pool a bundle belongs to. Orchard and Ironwood share the same
+/// `orchard::pczt::Bundle` representation, so this distinguishes them (e.g. in
+/// error messages) without a free-form string.
+#[cfg(feature = "cypherpunk")]
+#[derive(Clone, Copy)]
+pub(crate) enum ShieldedPool {
+    Orchard,
+    #[cfg(zcash_unstable = "nu6.3")]
+    Ironwood,
+}
+
+#[cfg(feature = "cypherpunk")]
+impl ShieldedPool {
+    pub(crate) fn label(self) -> &'static str {
+        match self {
+            ShieldedPool::Orchard => "Orchard",
+            #[cfg(zcash_unstable = "nu6.3")]
+            ShieldedPool::Ironwood => "Ironwood",
+        }
+    }
+}
+
 /// Returns the supported account declared by a shielded spend derivation that
 /// belongs to this seed. Missing or different seed fingerprints are not ours
 /// and return `None`; matching fingerprints with paths outside
@@ -109,8 +131,9 @@ pub(crate) fn matching_seed_supported_orchard_account(
     seed_fingerprint: &[u8; 32],
     derivation: Option<&zcash_vendor::orchard::pczt::Zip32Derivation>,
     coin_type: u32,
-    pool_label: &str,
+    pool: ShieldedPool,
 ) -> Result<Option<zcash_vendor::zip32::AccountId>, crate::errors::ZcashError> {
+    let pool_label = pool.label();
     let Some(derivation) = derivation else {
         return Ok(None);
     };
diff --git a/rust/apps/zcash/src/pczt/parse.rs b/rust/apps/zcash/src/pczt/parse.rs
index 567b58e..d49be3b 100644
--- a/rust/apps/zcash/src/pczt/parse.rs
+++ b/rust/apps/zcash/src/pczt/parse.rs
@@ -35,6 +35,9 @@ use zcash_vendor::{
 #[cfg(feature = "cypherpunk")]
 use super::structs::ParsedOrchard;
 use super::structs::{ParsedFrom, ParsedPczt, ParsedTo, ParsedTransparent};
+
+#[cfg(feature = "cypherpunk")]
+use super::ShieldedPool;
 use crate::errors::ZcashError;
 
 const ZEC_DIVIDER: u32 = 100_000_000;
@@ -179,7 +182,7 @@ pub fn parse_pczt_cypherpunk<P: consensus::Parameters>(
 
     let verifier = Verifier::new(pczt.clone())
         .with_orchard(|bundle| {
-            parsed_orchard = parse_orchard(params, seed_fingerprint, ufvk, bundle, "Orchard")
+            parsed_orchard = parse_orchard(params, seed_fingerprint, ufvk, bundle, ShieldedPool::Orchard)
                 .map_err(pczt::roles::verifier::OrchardError::Custom)?;
             Ok(())
         })
@@ -188,7 +191,7 @@ pub fn parse_pczt_cypherpunk<P: consensus::Parameters>(
     let verifier = if should_process_ironwood {
         verifier
             .with_ironwood(|bundle| {
-                parsed_ironwood = parse_orchard(params, seed_fingerprint, ufvk, bundle, "Ironwood")
+                parsed_ironwood = parse_orchard(params, seed_fingerprint, ufvk, bundle, ShieldedPool::Ironwood)
                     .map_err(pczt::roles::verifier::OrchardError::Custom)?;
                 Ok(())
             })
@@ -514,7 +517,7 @@ fn parse_orchard<P: consensus::Parameters>(
     seed_fingerprint: &[u8; 32],
     ufvk: &UnifiedFullViewingKey,
     orchard: &orchard::pczt::Bundle,
-    pool_label: &str,
+    pool: ShieldedPool,
 ) -> Result<Option<ParsedOrchard>, ZcashError> {
     let mut parsed_orchard = ParsedOrchard::new(vec![], vec![]);
     orchard.actions().iter().try_for_each(|action| {
@@ -527,7 +530,7 @@ fn parse_orchard<P: consensus::Parameters>(
                 parsed_orchard.add_from(parsed_from);
             }
         }
-        let parsed_to = parse_orchard_output(params, ufvk, action, pool_label)?;
+        let parsed_to = parse_orchard_output(params, ufvk, action, pool)?;
         if !parsed_to.get_is_dummy() {
             parsed_orchard.add_to(parsed_to);
         }
@@ -616,8 +619,9 @@ fn parse_orchard_output<P: consensus::Parameters>(
     params: &P,
     ufvk: &UnifiedFullViewingKey,
     action: &orchard::pczt::Action,
-    pool_label: &str,
+    pool: ShieldedPool,
 ) -> Result<ParsedTo, ZcashError> {
+    let pool_label = pool.label();
     let output = action.output();
     let fvk = ufvk.orchard().ok_or(ZcashError::InvalidDataError(
         "orchard is not present in ufvk".to_string(),
diff --git a/rust/apps/zcash/src/pczt/sign.rs b/rust/apps/zcash/src/pczt/sign.rs
index 565a63a..62bfdbf 100644
--- a/rust/apps/zcash/src/pczt/sign.rs
+++ b/rust/apps/zcash/src/pczt/sign.rs
@@ -350,23 +350,7 @@ fn collect_transparent_signing_keys(
 }
 
 #[cfg(feature = "cypherpunk")]
-#[derive(Clone, Copy)]
-enum ShieldedPool {
-    Orchard,
-    #[cfg(zcash_unstable = "nu6.3")]
-    Ironwood,
-}
-
-#[cfg(feature = "cypherpunk")]
-impl ShieldedPool {
-    fn label(self) -> &'static str {
-        match self {
-            ShieldedPool::Orchard => "Orchard",
-            #[cfg(zcash_unstable = "nu6.3")]
-            ShieldedPool::Ironwood => "Ironwood",
-        }
-    }
-}
+use super::ShieldedPool;
 
 #[cfg(feature = "cypherpunk")]
 fn collect_orchard_signing_keys(
@@ -426,7 +410,7 @@ fn collect_orchard_bundle_signing_keys(
         if action.spend().value().is_none() {
             continue;
         }
-        if let Some(ask) = spend_authorizing_key_for_action(seed, action, pool_label)? {
+        if let Some(ask) = spend_authorizing_key_for_action(seed, action, pool)? {
             keys.push((index, ask));
         }
     }
@@ -437,15 +421,16 @@ fn collect_orchard_bundle_signing_keys(
 fn spend_authorizing_key_for_action(
     seed: &[u8],
     action: &orchard::pczt::Action,
-    pool_label: &str,
+    pool: ShieldedPool,
 ) -> Result<Option<orchard::keys::SpendAuthorizingKey>, ZcashError> {
+    let pool_label = pool.label();
     let fingerprint =
         calculate_seed_fingerprint(seed).map_err(|e| ZcashError::SigningError(e.to_string()))?;
     let Some(account_index) = super::matching_seed_supported_orchard_account(
         &fingerprint,
         action.spend().zip32_derivation().as_ref(),
         133,
-        pool_label,
+        pool,
     )?
     else {
         return Ok(None);