solana/agent: always submit signature verify transactions

The first transaction acquires a pseudo-lock by setting
initial_creation = true, which will fail if a signature account
already exists. However, this is unsafe since the operation
consists of multiple operations and is not atomic - if the first
validator fails to submit a full set of signature transactions,
other guardians will not retry submitting signature verification txs.

We disable this mechanism to never set initial_creation, which
causes guardians to spend more fees in exchange for fault tolerance.

Instead of failing with an AlreadyExists error, duplicate transactions
will now succeed as a no-op and all nodes will attempt to submit
the full series of signature transactions.

Co-authored-by: Hendrik Hofstadt <hendrik@nexantic.com>
Change-Id: I0c418497f19cc97c9ae7a11b206035d6e70c1b66

solana/agent/src/main.rs

@@ -253,7 +253,7 @@ fn pack_sig_verification_txs<'a>(
         let payload = VerifySigPayload {
             signers: signature_status,
             hash: vaa_hash,
-            initial_creation: tx_index == 0,
+            initial_creation: false,
         };
 
         let verify_ix = match verify_signatures(