Example: x402 pre-send guard before EVM agent transaction broadcast

[cakirasim]

I published a small x402 package that fits the AgentKit transaction path as a pre-send guard:

• npm: https://www.npmjs.com/package/nishvault-preflight-buy
• discovery: https://api.nishvault.com/.well-known/x402
• first unpaid 402: https://api.nishvault.com/first-unpaid-402?autorun=1

The use case is narrow: before an autonomous EVM agent broadcasts a transaction, run one x402-paid preflight to inspect revert risk, fee context, and likely call outcome.

Suggested example shape:

agent chooses action -> transaction payload built -> Nishvault pre-send guard -> wallet send/broadcast

The package exposes:

• nishvault-guard-tx
• createViemPreflightGuard
• createEthersPreflightGuard
• createEip1193PreflightGuard
• createAgentGuardStep

Would an example PR showing this as a pre-broadcast guard step be useful for the AgentKit examples/docs?

[cakirasim]

Mainnet-ready update: Nishvault is now live as a real Base mainnet x402 pre-send guard.

• Live API: https://api.nishvault.com
• First real buyer challenge: https://api.nishvault.com/first-real-buyer
• x402 metadata: https://api.nishvault.com/.well-known/x402
• Network: eip155:8453 Base mainnet
• Price: $0.01 real USDC
• npm: nishvault-preflight-buy@0.1.3

If your AgentKit agent sends Base transactions, the intended test is now one command before broadcast:

npx --package nishvault-preflight-buy nishvault-guard-tx -- --seller-url https://api.nishvault.com --to 0x2222222222222222222222222222222222222222 --data 0x --value 0x0

The goal is not another simulator page. It is the guard step immediately before sendTransaction: unpaid 402 discovery first, then one real $0.01 x402 paid preflight, then Base mainnet settlement/wallet-credit proof.

[cakirasim]

Follow-up for the first real buyer path: I am looking for exactly one AgentKit/Base example that already reaches a transaction broadcast step.

If any AgentKit agent sends Base transactions, the workflow slot is immediately before sendTransaction:

npx --package nishvault-preflight-buy nishvault-guard-tx -- --seller-url https://api.nishvault.com --to 0x2222222222222222222222222222222222222222 --data 0x --value 0x0

This is live on Base mainnet (eip155:8453) at $0.01 real USDC. Success signal is external_mainnet_paid_request plus seller wallet-credit. First buyer challenge: https://api.nishvault.com/first-real-buyer

[cakirasim]

Receipt-producing launch gate update: Nishvault now has a dedicated AgentKit patch surface and receipt output, not just a simulator-style endpoint.

If an AgentKit/Base example reaches broadcast, the exact patch shape is: transaction built -> nishvault-guard-tx / SDK wrapper -> PRE_SEND_PROOF_RECEIPT -> sendTransaction.

Launch gate: https://api.nishvault.com/required-before-send
Receipt preview: https://api.nishvault.com/proof-receipt
AgentKit patch surface: https://api.nishvault.com/agentkit-patch
First external buyer slot: https://api.nishvault.com/first-real-buyer

This is now a receipt-producing launch gate, not a simulator.