fix(legacy): align coinjoin behavior with core

### legacy/firmware/.changelog.d/+coinjoin-preauthorization.changed
@@ -0,0 +1 @@
+Restrict which message types may use an authorization granted by DoPreauthorized or a path unlocked by UnlockPath.

### legacy/firmware/fsm.c
@@ -453,6 +453,32 @@ void fsm_abortWorkflows(void) {
 #endif
 }
 
+// Which messages may make use of an authorization granted by DoPreauthorized.
+static bool fsm_isPreauthorizedMessage(MessageType message_type) {
+  return message_type == MessageType_MessageType_SignTx ||
+         message_type == MessageType_MessageType_GetOwnershipProof;
+}
+
+// Which messages may make use of a path unlocked by UnlockPath.
+static bool fsm_isUnlockPathMessage(MessageType message_type) {
+  return message_type == MessageType_MessageType_GetAddress ||
+         message_type == MessageType_MessageType_GetPublicKey ||
+         message_type == MessageType_MessageType_SignTx;
+}
+
+void fsm_preMsgCleanup(MessageType message_type) {
+  // Drop the authorization and the unlocked path before processing a message
+  // which they do not apply to, so that it cannot gain access to the SLIP-25
+  // account without the user's confirmation.
+  if (!fsm_isPreauthorizedMessage(message_type)) {
+    authorization_type = 0;
+  }
+
+  if (!fsm_isUnlockPathMessage(message_type)) {
+    unlock_path = 0;
+  }
+}
+
 void fsm_postMsgCleanup(MessageType message_type) {
   if (message_type != MessageType_MessageType_DoPreauthorized) {
     authorization_type = 0;

### legacy/firmware/fsm.h
@@ -163,6 +163,7 @@ bool fsm_getOwnershipId(uint8_t *script_pubkey, size_t script_pubkey_size,
                         uint8_t ownership_id[32]);
 
 void fsm_abortWorkflows(void);
+void fsm_preMsgCleanup(MessageType message_type);
 void fsm_postMsgCleanup(MessageType message_type);
 
 #endif

### legacy/firmware/messages.c
@@ -61,6 +61,7 @@ void MessageProcessFunc(char type, char dir, uint16_t msg_id, void *ptr) {
   const struct MessagesMap_t *m = MessagesMap;
   while (m->type) {
     if (type == m->type && dir == m->dir && msg_id == m->msg_id) {
+      fsm_preMsgCleanup(msg_id);
       m->process_func(ptr);
       fsm_postMsgCleanup(msg_id);
       return;

### tests/device_tests/bitcoin/test_authorize_coinjoin.py
@@ -724,6 +724,33 @@ def test_cancel_authorization(session: Session):
         )
 
 
+def test_preauthorized_message_type(session: Session):
+    # Ensure that a preauthorization cannot be used by a message type that it wasn't granted for.
+
+    btc.authorize_coinjoin(
+        session,
+        coordinator="www.example.com",
+        max_rounds=10,
+        max_coordinator_fee_rate=500_000,  # 0.5 %
+        max_fee_per_kvbyte=3500,
+        n=parse_path("m/10025h/1h/0h/1h"),
+        coin_name="Testnet",
+        script_type=messages.InputScriptType.SPENDTAPROOT,
+    )
+
+    # Only SignTx and GetOwnershipProof may use the preauthorization, so GetAddress must
+    # not gain access to the SLIP-25 account without going through UnlockPath.
+    session.call(messages.DoPreauthorized(), expect=messages.PreauthorizedRequest)
+
+    with pytest.raises(TrezorFailure, match="Forbidden key path"):
+        btc.get_address(
+            session,
+            "Testnet",
+            parse_path("m/10025h/1h/0h/1h/0/0"),
+            script_type=messages.InputScriptType.SPENDTAPROOT,
+        )
+
+
 def test_get_public_key(session: Session):
     ACCOUNT_PATH = parse_path("m/10025h/1h/0h/1h")
     EXPECTED_XPUB = "tpubDEMKm4M3S2Grx5DHTfbX9et5HQb9KhdjDCkUYdH9gvVofvPTE6yb2MH52P9uc4mx6eFohUmfN1f4hhHNK28GaZnWRXr3b8KkfFcySo1SmXU"