@leash/core

• Agent + treasury — treasuryPda(asset) derives the Asset Signer PDA used as payTo and the on-chain owner of the agent’s funds. deriveAgentTreasuryAddress(asset) and deriveAgentTreasuryAta({ asset, mint }) do the same derivations using @solana/kit only (no Umi runtime), so buyer/seller code can resolve the treasury + token ATA without dragging in Metaplex’s Umi context.
• Policy — evaluate(rules, request, ledger, pause) returns a pure decision (allow / deny + reason). Buyer/seller kits also stamp rejected on receipts when the gate allowed a call but the payment did not settle.
• Networks — caip2ForNetwork('solana-devnet') returns the wire-level CAIP-2 chain id; the inverse networkFromCaip2('solana:EtWTRABZ…') returns the friendly Leash slug used on receipts.
• Hashing — canonicalJson, sha256Hex, requestHash, paymentRequirementsHash, computeReceiptHash, finalizeReceipt, verifyReceiptChain. All hashing uses @noble/hashes so it runs in any JS environment (Node, browser, edge).
• x402 client adapter — createSvmBuyerFetch({ signer, networks, rpcUrl, preferredAsset?, sourceTokenAccount? }) wraps wrapFetchWithPayment from @x402/fetch with ExactSvmScheme (or LeashDelegateExactSvmScheme when sourceTokenAccount is set) and a ClientSvmSigner. Optional preferredAsset (SPL mint string) selects which accepts[] row to pay when the seller lists several stables; if set and no row matches, the client throws (preferred_asset_unavailable) instead of silently paying a different mint. @leash/buyer-kit wires this via preferredCurrency (USDC / USDT / USDG).
• Payment-link discovery — fetchPaymentLinkMeta() fetches and type-checks the browser-friendly GET /x/<id> metadata payload exposed by the web app; buildPaymentLinkMeta() produces it on the server.
• Payment envelope — buildLeashEnvelope(receipt, { origin }) produces the compact LeashPaymentEnvelope that gets stamped onto webhooks, response headers, and wrap_receipt bodies after a settled payment.
• X-Leash-* headers — buildLeashHeaders(envelope, headers) and parseLeashHeaders(response) round-trip the envelope through HTTP responses without sellers / buyers misspelling header names. LEASH_HEADERS is the canonical name map; LEASH_CALLBACK_HEADER is the per-call webhook opt-in (x-leash-callback).
• Webhook payload — buildWebhookPayload({ envelope, response }) and parseWebhookPayload(json) produce / validate the JSON body Leash POSTs to endpoint.webhook_url. Versioned (v: '0.1') and discriminated (kind: 'leash.payment.settled') so downstream agents can route safely.
• Token registry — KNOWN_TOKENS, lookupToken(mint, network), lookupTokenBySymbol(symbol, network), KNOWN_STABLE_SYMBOLS, currencyForAsset(mint, network), pinnedMints(network), defaultUsdcMint(network). Stables on mainnet + devnet plus a few bluechips, indexed for UI surfaces.
• Format helpers — atomicToDecimal, decimalToAtomic, formatTokenBalance, formatReceiptPrice, formatReceiptPriceUsd. Use these instead of hand-rolled *1_000_000 math; they pull decimals from the registry so Token-2022 stables don’t silently truncate.
• Explorer links — transactionExplorerUrl, addressExplorerUrl, agentExplorerUrl. Solscan by default; pass { provider: 'solana-explorer' } for the official explorer.
• Treasury balances — listSplBalances({ owner, rpcUrl, network }) enumerates SPL + Token-2022 balances and pins missing stables with zero so UIs always render them.
• Kill switch — readPauseFromEnv, createPauseResolver. The buyer’s policy gate honours these so a single env flip (or admin RPC) can halt every spend immediately.
• Treasury helpers — getTreasuryBalance, buildWithdrawTx (stub for v0.1).

​

Agent treasury PDA

import { deriveAgentTreasuryAddress, deriveAgentTreasuryAta } from '@leash/core';

const treasury = await deriveAgentTreasuryAddress('33QvAYjEiK8UMrmpy3LW6W8v2wpPMahnw7Jvr7JpeQrR');

// Resolve the USDC ATA the agent treasury would receive into.
const { treasury: t, ata } = await deriveAgentTreasuryAta({
  asset: '33QvAYjEiK8UMrmpy3LW6W8v2wpPMahnw7Jvr7JpeQrR',
  mint: '4zMMC9srt5Ri5X14GAgXhaHii3GnPAEERYPJgZJDncDU', // USDC devnet
});

​

Why a separate adapter?

import { createSvmBuyerFetch } from '@leash/core/x402';

const paidFetch = createSvmBuyerFetch({
  signer, // @solana/kit TransactionPartialSigner
  networks: ['solana-devnet'],
  rpcUrl: 'https://api.devnet.solana.com',
  // Optional: SPL mint to prefer when the seller sends multiple `accepts[]`.
  // Must match one of those rows or the next paid fetch throws.
  // preferredAsset: '4F6PM96JJxngmHnZLBh9n58RH4aTVNWvDs2nuwrT5BP7', // devnet USDG
});

const res = await paidFetch('https://api.example.com/quote');

import { fetchPaymentLinkMeta } from '@leash/core';

// Variant 1: full shareable URL
const metaA = await fetchPaymentLinkMeta('https://yourapp.com/x/uhnb6e1zm');

// Variant 2: base host + endpoint id
const metaB = await fetchPaymentLinkMeta('https://yourapp.com', 'uhnb6e1zm');

console.log(metaA.endpoint.price); // "$0.001"
console.log(metaA.endpoint.currency); // "USDC"
console.log(metaA.endpoint.accepts_currencies); // e.g. ["USDG"]
console.log(metaB.endpoint.method); // "POST"

​

Settlement envelope, headers, and webhooks

import {
  buildLeashEnvelope,
  buildLeashHeaders,
  parseLeashHeaders,
  buildWebhookPayload,
  parseWebhookPayload,
  LEASH_HEADERS,
  LEASH_CALLBACK_HEADER,
} from '@leash/core';

// SELLER side: stamp envelope onto response headers + ship a webhook.
const envelope = buildLeashEnvelope(earnReceipt, { origin: 'https://app.example.com' });
const headers = buildLeashHeaders(envelope, new Headers(res.headers));
const body = JSON.stringify(buildWebhookPayload({ envelope, response: parsedBody }));

// BUYER side: parse the headers off the response without misspelling names.
const parsed = parseLeashHeaders(response);
console.log(parsed.txSig, parsed.receiptHash);

// Per-call webhook opt-in: buyers attach `x-leash-callback: <url>` and the
// seller delivers the same payload to that URL in addition to its own
// `endpoint.webhook_url`.
fetch(url, { headers: { [LEASH_CALLBACK_HEADER]: 'https://my-agent.example/webhook' } });

​

Token registry, formatters, and explorer links

import {
  KNOWN_TOKENS,
  defaultUsdcMint,
  formatReceiptPriceUsd,
  formatTokenBalance,
  lookupToken,
  listSplBalances,
  transactionExplorerUrl,
} from '@leash/core';

const usdc = defaultUsdcMint('devnet'); // canonical mint
const meta = lookupToken(usdc.mint, 'devnet'); // { decimals: 6, ... }

formatTokenBalance('1500000', usdc.mint, 'devnet'); // "1.5"
formatReceiptPriceUsd({ amount: '2', currency: 'USDC' }); // "$0.000002"

const balances = await listSplBalances({
  owner: 'CTd5VBFYJnGDGv5DbhWfPmrQ96G5ibvmZiyRPURXNyox',
  rpcUrl: 'https://api.devnet.solana.com',
  network: 'devnet',
});

transactionExplorerUrl('5sig', { network: 'devnet' });
// 'https://solscan.io/tx/5sig?cluster=devnet'