Solana signing

This skill exposes a small foundation for building unsigned Solana transactions from chat. The plugin never sees a Solana private key — every state-changing tool returns a base64-encoded VersionedTransaction that the user signs in their wallet.

When to use this skill

• The user asks to "send SOL to X" or "transfer USDC to Y" from a Solana address they control.
• The user wants to inspect a Solana transaction someone else built before signing it.
• A more advanced Solana flow (Drift order, Marginfi deposit, Kamino borrow) builds on the foundation here — when those land, they will reuse lib/solana-sign.ts directly.

What the surface is

• chaingpt_solana_build_transfer_tx — build an unsigned transfer.
  • Native SOL when mint is omitted. Decimals: 9 (LAMPORTS_PER_SOL).
  • SPL Token (classic or Token-2022) when mint is provided. Decimals fetched from the mint account. Source + destination Associated Token Accounts derived automatically. Idempotent CreateATAIdempotent instruction included so first-time-recipient transfers work without an extra setup step.
  • acknowledgeMainnet: true required when network=mainnet. Same gate as the EVM tools.
• chaingpt_solana_decode_tx — decode an unsigned base64 versioned transaction for review (payer, blockhash, instruction count, program ids with annotations).

Custody model

Identical to the rest of the plugin: custody-free. The plugin builds the transaction; the user signs it elsewhere. There is no MCP tool that accepts a secretKey, mnemonic, or seedPhrase parameter, and a unit test asserts this surface contract so future additions cannot accidentally break it.

If the user wants policy-gated signing, the agent wallet skill covers EVM, Solana, Tron and ERC-4337 signers. It is disabled by default (CHAINGPT_AGENT_WALLET_ENABLED=true in the launch environment enables it).

Mainnet safety gate

When network=mainnet, the build tool refuses unless acknowledgeMainnet=true is also passed. The refusal message lists what to verify before re-call (recipient address, amount, mint, network). This matches feedback_mainnet_default: mainnet is the target, but mainnet transactions require an explicit ack.

Typical flow

User: "Build a 0.5 USDC transfer from 7uDsTC...EUd to 9WzDXw...WWM on mainnet"
Agent: chaingpt_solana_build_transfer_tx({
  from: "7uDsTC1u4eRkxsfvQHvi3vCSqGBHc4uS9wpYbobcdEUd",
  to:   "9WzDXwBbmkg8ZTbNMqUxvQRAyrZzDsGYdLVL9zYtAWWM",
  amount: "0.5",
  mint:  "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",  // USDC mint
  network: "mainnet",
  acknowledgeMainnet: true
})
→ returns:
  - decoded summary (from ATA, to ATA, amount in base units, decimals)
  - the base64 VersionedTransaction
  - the blockhash + lastValidBlockHeight
  - next-step instructions for the signer
User: paste base64 into Phantom → review → sign → submit.

RPC endpoints

Default public RPC fallback per network:

Override via SOLANA_RPC_URL env var (Helius / QuickNode / Triton recommended for production loads).

Why TransferChecked instead of Transfer

The classic SPL Token program has two transfer instructions:

• Transfer (discriminator 3): minimal — source, destination, owner, amount.
• TransferChecked (discriminator 12): also takes mint + decimals and the runtime verifies they match the source account's mint.

We always emit TransferChecked. The mint/decimals check prevents an attacker from swapping an unrelated ATA into the destination slot to redirect funds.

What this skill does NOT do (yet)

• Drift signed orders — read-only via chaingpt_drift_* today. Signed placePerpOrder, deposit, withdraw are queued as follow-up PRs that will use the foundation here.
• Marginfi signed lending — read-only today. Same story.
• Kamino signed lending — read-only today. Same story.
• Jupiter swaps — already supported via chaingpt_dex_jupiter_quote (the unsigned-swap-tx call from Jupiter's API is returned directly; no foundation needed).
• NFT transfers / Metaplex — out of scope for the foundation.

When you build those follow-ups, the pattern is:

1. Import buildVersionedTransaction, serializeUnsigned, makeConnection, parseAddress from lib/solana-sign.ts.
2. Build the protocol-specific TransactionInstruction[] (account derivation + IDL-encoded data).
3. Call buildVersionedTransaction({ payer, instructions, connection }).
4. Return serializeUnsigned(tx) plus a decoded summary.
5. Gate any mainnet build behind acknowledgeMainnet:true.
6. Add a vitest with mocked Connection.getLatestBlockhash so the test never touches the network.

Reference

• mcp-server/src/lib/solana-sign.ts — utilities (RPC fallback, parseAddress, instruction builders, ATA derivation, mint info fetch, v0 message build, base64 ser/de).
• mcp-server/src/tools/solana.ts — tool surface (build_transfer_tx, decode_tx).
• mcp-server/src/__tests__/solana.test.ts — 29 cases.