fix(cli): accept base58-encoded transaction_message in vault_transaction_create (closes #159)

[cryptomotifs]

Summary

Closes #159.

--transaction-message on squads-multisig-cli vault-transaction-create is typed as Vec<u8>, which clap parses as one byte per --transaction-message invocation. A real VaultTransactionMessage is many bytes long, so as-written there is no way to actually pass one through this argument — the CLI accepts the flag but cannot accept a real message (which is what #159 reports).

Fix

Take the message as a single base58-encoded string and decode it inside a clap::value_parser. The decoded Vec<u8> flows through the rest of the function unchanged — the on-chain instruction continues to receive the same bytes.

fn parse_base58_transaction_message(s: &str) -> Result<Vec<u8>, String> {
    solana_sdk::bs58::decode(s)
        .into_vec()
        .map_err(|e| format!(\"invalid base58 in --transaction-message: {e}\"))
}

#[arg(long, value_parser = parse_base58_transaction_message)]
transaction_message: Vec<u8>,

Base58 matches the rest of the Squads CLI (multisig_pubkey is already base58 parsed via Pubkey::from_str) and bs58 is already available via solana_sdk so no new dependency is added.

Usage after fix

squads-multisig-cli vault-transaction-create \
  --keypair ./keypair.json \
  --multisig-pubkey 6Mz4...Asdf \
  --vault-index 0 \
  --transaction-message <base58-encoded-VaultTransactionMessage>

Test plan

• Diff compiles with the existing solana-sdk dependency (no new crate added).
• CI: please run the cli build/test suite — happy to follow up if maintainers want a small unit test for the parser fn.

🤖 Generated with Claude Code

[vercel]

@cryptomotifs is attempting to deploy a commit to the squads Team on Vercel.

A member of the Team first needs to authorize it.