fix: FVK account default bug + remove redundant account=0 in tests

Change zcash_get_orchard_fvk account default from 0 to None.
Only serialize account field when explicitly set — firmware derives
from address_n[2] otherwise. Same fix as zcash_sign_pczt.

Update tests to rely on address_n path derivation.

Author: BitHighlander

keepkeylib/client.py

@@ -1607,14 +1607,11 @@ def ton_sign_tx(self, address_n, raw_tx):
 
     # ── Zcash Orchard ──────────────────────────────────────────
     @expect(zcash_proto.ZcashOrchardFVK)
-    def zcash_get_orchard_fvk(self, address_n, account=0, show_display=False):
-        return self.call(
-            zcash_proto.ZcashGetOrchardFVK(
-                address_n=address_n,
-                account=account,
-                show_display=show_display,
-            )
-        )
+    def zcash_get_orchard_fvk(self, address_n, account=None, show_display=False):
+        kwargs = dict(address_n=address_n, show_display=show_display)
+        if account is not None:
+            kwargs['account'] = account
+        return self.call(zcash_proto.ZcashGetOrchardFVK(**kwargs))
 
     @session
     def zcash_sign_pczt(self, address_n, actions, account=None,

tests/test_msg_zcash_orchard.py

@@ -48,7 +48,7 @@ def test_fvk_field_ranges(self):
 
         # ZIP-32 Orchard path: m/32'/133'/0'
         address_n = [0x80000000 + 32, 0x80000000 + 133, 0x80000000]
-        resp = self.client.zcash_get_orchard_fvk(address_n=address_n, account=0)
+        resp = self.client.zcash_get_orchard_fvk(address_n=address_n)
 
         ak = resp.ak
         nk = resp.nk
@@ -84,7 +84,7 @@ def test_fvk_reference_vectors(self):
         self.setup_mnemonic_allallall()
 
         address_n = [0x80000000 + 32, 0x80000000 + 133, 0x80000000]
-        resp = self.client.zcash_get_orchard_fvk(address_n=address_n, account=0)
+        resp = self.client.zcash_get_orchard_fvk(address_n=address_n)
 
         ak_hex = binascii.hexlify(resp.ak).decode()
         nk_hex = binascii.hexlify(resp.nk).decode()
@@ -100,8 +100,8 @@ def test_fvk_consistency_across_calls(self):
 
         address_n = [0x80000000 + 32, 0x80000000 + 133, 0x80000000]
 
-        resp1 = self.client.zcash_get_orchard_fvk(address_n=address_n, account=0)
-        resp2 = self.client.zcash_get_orchard_fvk(address_n=address_n, account=0)
+        resp1 = self.client.zcash_get_orchard_fvk(address_n=address_n)
+        resp2 = self.client.zcash_get_orchard_fvk(address_n=address_n)
 
         self.assertTrue(resp1.ak == resp2.ak, "ak must be deterministic")
         self.assertTrue(resp1.nk == resp2.nk, "nk must be deterministic")
@@ -127,7 +127,7 @@ def test_fvk_abandon_mnemonic(self):
         self.setup_mnemonic_abandon()
 
         address_n = [0x80000000 + 32, 0x80000000 + 133, 0x80000000]
-        resp = self.client.zcash_get_orchard_fvk(address_n=address_n, account=0)
+        resp = self.client.zcash_get_orchard_fvk(address_n=address_n)
 
         # Check field ranges (not reference values — just validity)
         self.assertTrue(resp.ak[31] & 0x80 == 0, "ak sign bit must be 0 for abandon mnemonic")