Add forwardToArbiter docs and named address constants

docs.json

@@ -102,6 +102,7 @@
             "pages": [
               "sdk/merchant/getting-started",
               "sdk/helpers/refundable",
+              "sdk/helpers/forward-to-arbiter",
               "sdk/merchant/quickstart",
               "sdk/merchant/refund-handling"
             ]

sdk/helpers/forward-to-arbiter.mdx

@@ -0,0 +1,140 @@
+---
+title: "forwardToArbiter()"
+description: "Forward settlement data to an arbiter service for quality evaluation"
+icon: "arrow-right"
+---
+
+The `forwardToArbiter()` function creates an `onAfterSettle` hook that forwards the response body and payment payload to an arbiter service. It runs fire-and-forget so it never blocks the response to the client.
+
+- Only fires for successful **commerce** scheme settlements
+- POSTs `{ responseBody, transaction, paymentPayload }` to `{arbiterUrl}/verify`
+- Errors are silently caught so an unavailable arbiter cannot break the payment flow
+
+## Usage
+
+```typescript
+import { forwardToArbiter } from '@x402r/helpers';
+
+const resourceServer = new x402ResourceServer(facilitatorClient)
+  .register(networkId, new EscrowServerScheme())
+  .onAfterSettle(
+    forwardToArbiter('http://arbiter:3001')
+  );
+```
+
+## Function signature
+
+```typescript
+function forwardToArbiter(
+  arbiterUrl: string,
+  options?: ForwardToArbiterOptions
+): (context: SettleResultContext) => Promise<void>
+```
+
+### Parameters
+
+| Parameter | Type | Description |
+|-----------|------|-------------|
+| `arbiterUrl` | `string` | Base URL of your arbiter service (e.g. `http://arbiter:3001`) |
+| `options` | `ForwardToArbiterOptions` | Optional configuration (see below) |
+
+### Options
+
+```typescript
+interface ForwardToArbiterOptions {
+  /** Custom error handler. Defaults to `console.warn`. */
+  onError?: (error: unknown) => void;
+}
+```
+
+## Payload shape
+
+When a commerce settlement succeeds, the hook POSTs the following JSON to `{arbiterUrl}/verify`:
+
+```typescript
+{
+  responseBody: string;       // UTF-8 encoded response body
+  transaction: string;        // Settlement transaction hash
+  paymentPayload: {
+    x402Version: number;
+    accepted: {
+      scheme: string;         // e.g. "commerce"
+      network: string;        // e.g. "eip155:84532"
+      // ...other accepted fields
+    };
+    payload: {
+      paymentInfo: {
+        operator: string;
+        payer: string;
+        receiver: string;
+        // ...full PaymentInfo
+      };
+    };
+  };
+}
+```
+
+<Tip>
+Arbiters that need `paymentInfo` for `release()` can read it directly from `paymentPayload.payload.paymentInfo` — no extra RPC call needed.
+</Tip>
+
+## Error handling
+
+By default, fetch errors are logged with `console.warn`. You can override this with a custom handler:
+
+```typescript
+import { forwardToArbiter } from '@x402r/helpers';
+
+const resourceServer = new x402ResourceServer(facilitatorClient)
+  .register(networkId, new EscrowServerScheme())
+  .onAfterSettle(
+    forwardToArbiter('http://arbiter:3001', {
+      onError: (err) => sentry.captureException(err),
+    })
+  );
+```
+
+Errors are wrapped in an `X402rError` with the arbiter URL and request details for easier debugging.
+
+## Skipped scenarios
+
+The hook silently returns without making a request when:
+
+- The settlement was not successful (`context.result.success === false`)
+- The scheme is not `commerce` (e.g. direct or other custom schemes)
+- No response body is available in the transport context
+
+## Address re-exports
+
+The `@x402r/helpers` package re-exports chain-invariant address constants from `@x402r/core` for convenience:
+
+```typescript
+import {
+  authCaptureEscrow,
+  tokenCollector,
+  protocolFeeConfig,
+  arbiterRegistry,
+  receiverRefundCollector,
+  usdcTvlLimit,
+  factories,
+  conditions,
+  getChainConfig,
+  supportedChainIds,
+} from '@x402r/helpers';
+```
+
+These are the same CREATE3 addresses available from `@x402r/core`. You can import from either package depending on which you already have installed.
+
+## Next steps
+
+<CardGroup cols={2}>
+  <Card title="refundable()" icon="wrench" href="/sdk/helpers/refundable">
+    Configure escrow options and fee bounds.
+  </Card>
+  <Card title="Arbiter SDK" icon="gavel" href="/sdk/arbiter/quickstart">
+    Build an arbiter that processes forwarded settlements.
+  </Card>
+  <Card title="Examples" icon="code" href="/sdk/examples">
+    See working merchant server examples.
+  </Card>
+</CardGroup>

sdk/helpers/refundable.mdx

@@ -155,6 +155,9 @@ app.get('/api/resource', (req, res) => {
 ## Next Steps
 
 <CardGroup cols={2}>
+  <Card title="forwardToArbiter()" icon="arrow-right" href="/sdk/helpers/forward-to-arbiter">
+    Forward settlement data to an arbiter for evaluation.
+  </Card>
   <Card title="Deploy Operator" icon="rocket" href="/sdk/deploy-operator">
     Deploy a PaymentOperator to use with refundable().
   </Card>

sdk/installation.mdx

@@ -37,18 +37,43 @@ Create `publicClient` and `walletClient` using [viem](https://viem.sh/docs/clien
 
 ## Contract Addresses
 
-Get the deployed contract addresses from the network config:
+All protocol contracts use CREATE3 addresses that are the same on every supported chain. You can import them directly as named constants or look them up from a chain config:
 
-```typescript
-import { getNetworkConfig } from '@x402r/core';
+<Tabs>
+  <Tab title="Named constants">
+    ```typescript
+    import {
+      authCaptureEscrow,
+      tokenCollector,
+      protocolFeeConfig,
+      arbiterRegistry,
+      receiverRefundCollector,
+      usdcTvlLimit,
+      factories,
+      conditions,
+    } from '@x402r/core';
+
+    console.log(authCaptureEscrow);       // 0xBC15…
+    console.log(factories.paymentOperator); // 0x3Cd5…
+    console.log(conditions.payer);          // 0x808b…
+    ```
+  </Tab>
+  <Tab title="Chain config">
+    ```typescript
+    import { getChainConfig } from '@x402r/core';
 
-const config = getNetworkConfig('eip155:84532'); // Base Sepolia
+    const config = getChainConfig(84532); // Base Sepolia
+
+    console.log(config.authCaptureEscrow); // Escrow contract
+    console.log(config.arbiterRegistry);   // ArbiterRegistry contract
+    console.log(config.usdc);              // USDC token address (chain-specific)
+    ```
+  </Tab>
+</Tabs>
 
-console.log(config.authCaptureEscrow); // Escrow contract
-console.log(config.refundRequest);     // RefundRequest contract
-console.log(config.arbiterRegistry);   // ArbiterRegistry contract
-console.log(config.usdc);             // USDC token address
-```
+<Tip>
+The named constants and `getChainConfig()` return identical addresses. Use named constants when you don't need the chain-specific USDC address.
+</Tip>
 
 <Note>
 Network identifiers use the [EIP-155](https://eips.ethereum.org/EIPS/eip-155) format: `eip155:<chainId>`. For Base Sepolia, use `'eip155:84532'`. For Base Mainnet, use `'eip155:8453'`.

sdk/overview.mdx

@@ -28,7 +28,7 @@ The SDK is organized into packages designed for specific roles in the payment ec
     SDK for arbiters to resolve disputes and manage refund decisions.
   </Card>
   <Card title="@x402r/helpers" icon="wrench" href="/sdk/helpers/refundable">
-    Framework-agnostic helper to mark x402 payment options as refundable with escrow configuration.
+    Framework-agnostic helpers: `refundable()` for escrow configuration, `forwardToArbiter()` for arbiter integration, and re-exported address constants.
   </Card>
 </CardGroup>