fix(wasm-solana): return empty string for unsigned (all-zeros) signatures

The parse_transaction function was blindly converting all signatures to
base58, causing all-zeros placeholder signatures to become
'1111111111111111111111111111111111111111111111111111111111111111'.

Now checks each signature for all-zeros and returns empty string instead,
matching the behavior of Transaction::id() which returns None for
unsigned transactions.

BTC-3025

Author: lcovar

packages/wasm-solana/src/parser.rs

@@ -153,8 +153,21 @@ pub fn parse_transaction(bytes: &[u8]) -> Result<ParsedTransaction, String> {
     // Note: Instruction combining (e.g., CreateAccount + StakeInitialize → StakingActivate)
     // is handled by TypeScript in mapWasmInstructionsToBitGoJS for flexibility
 
-    // Extract signatures as base58 strings
-    let signatures: Vec<String> = tx.signatures.iter().map(|s| s.to_string()).collect();
+    // Extract signatures as base58 strings.
+    // All-zeros signatures (unsigned placeholder slots) are returned as empty strings
+    // so the JS side can simply use `signatures[0] || 'UNAVAILABLE'`.
+    let signatures: Vec<String> = tx
+        .signatures
+        .iter()
+        .map(|s| {
+            let bytes: &[u8] = s.as_ref();
+            if bytes.iter().all(|&b| b == 0) {
+                String::new()
+            } else {
+                s.to_string()
+            }
+        })
+        .collect();
 
     Ok(ParsedTransaction {
         fee_payer,