fix: Update 8021 docs to include dataSuffix capability

docs/base-account/reference/core/capabilities/dataSuffix.mdx

@@ -0,0 +1,157 @@
+---
+title: "dataSuffix"
+description: "Append arbitrary data to transaction calldata for attribution tracking"
+---
+
+Defined in [ERC-8021](https://eip.tools/eip/8021)
+
+<Info>
+The dataSuffix capability allows apps to append arbitrary hex-encoded bytes to transaction calldata. This enables attribution tracking, allowing platforms to identify which app originated a transaction and distribute rewards accordingly.
+</Info>
+
+## Parameters
+
+<ParamField body="value" type="`0x${string}`" required>
+Hex-encoded bytes to append to the transaction calldata. This value is appended to the end of the calldata for each call in the batch.
+</ParamField>
+
+<ParamField body="optional" type="boolean">
+When `true`, the wallet may ignore the capability if it doesn't support it. When `false` or omitted, the wallet must support the capability or reject the request.
+</ParamField>
+
+## Returns
+
+<ResponseField name="dataSuffix" type="object">
+The data suffix capability configuration for the specified chain.
+
+<Expandable title="DataSuffix capability properties">
+<ResponseField name="supported" type="boolean">
+Indicates whether the wallet supports appending data suffixes to transaction calldata.
+</ResponseField>
+</Expandable>
+</ResponseField>
+
+## Example Usage
+
+<RequestExample>
+```typescript Check DataSuffix Support
+const capabilities = await provider.request({
+  method: 'wallet_getCapabilities',
+  params: [userAddress]
+});
+
+const dataSuffixSupport = capabilities["0x2105"]?.dataSuffix;
+```
+
+```typescript Send Transaction with DataSuffix
+const result = await provider.request({
+  method: "wallet_sendCalls",
+  params: [{
+    version: "1.0",
+    chainId: "0x2105",
+    from: userAddress,
+    calls: [{
+      to: "0x1234567890123456789012345678901234567890",
+      value: "0x0",
+      data: "0xa9059cbb000000000000000000000000..."
+    }],
+    capabilities: {
+      dataSuffix: {
+        value: "0x1234567890abcdef1234567890abcdef",
+        optional: true
+      }
+    }
+  }]
+});
+```
+</RequestExample>
+
+<ResponseExample>
+```json Capability Response (Supported)
+{
+  "0x2105": {
+    "dataSuffix": {
+      "supported": true
+    }
+  }
+}
+```
+
+```json Capability Response (Unsupported)
+{
+  "0x2105": {
+    "dataSuffix": {
+      "supported": false
+    }
+  }
+}
+```
+</ResponseExample>
+
+## Error Handling
+
+| Code | Message | Description |
+| ---- | ------- | ----------- |
+| 4100 | Data suffix not supported | Wallet does not support data suffix functionality |
+| 5700 | DataSuffix capability required | Transaction requires dataSuffix but wallet doesn't support it |
+
+## How It Works
+
+When a wallet receives a `dataSuffix` capability, the suffix is appended to `userOp.callData`. The suffix bytes are concatenated directly to the end of the calldata, making them available for onchain parsing and attribution.
+
+## Use Cases
+
+### Builder Codes Attribution
+
+The primary use case for `dataSuffix` is [Builder Codes](/base-chain/quickstart/builder-codes) attribution. Builder Codes are unique identifiers that allow apps to receive attribution for onchain activity they generate.
+
+```typescript
+import { Attribution } from "ox/erc8021";
+
+// Example: Using Builder Code with dataSuffix.
+// Using the ox/erc8021 package to generate the ERC-8021 suffix from your builder code.
+const builderCodeSuffix = Attribution.toDataSuffix({
+  codes: ['bc_foobar'], // Get your code from base.dev
+});
+
+await provider.request({
+  method: "wallet_sendCalls",
+  params: [{
+    version: "1.0",
+    chainId: "0x2105",
+    from: userAddress,
+    calls: [{
+      to: contractAddress,
+      value: "0x0",
+      data: swapCallData
+    }],
+    capabilities: {
+      dataSuffix: {
+        value: builderCodeSuffix,
+        optional: true
+      }
+    }
+  }]
+});
+```
+
+Register on [base.dev](https://base.dev) to get your Builder Code for proper attribution.
+
+## Best Practices
+
+1. **Use with Builder Codes**: Register on [base.dev](https://base.dev) to get your Builder Code for proper attribution
+2. **Set optional appropriately**: Use `optional: true` if your app can function without attribution tracking
+3. **Keep suffixes small**: Larger suffixes increase gas costs
+
+<Info>
+For wallet developers implementing dataSuffix support, see the [For Wallet Developers](/base-chain/quickstart/builder-codes#for-wallet-developers) section in the Builder Codes guide.
+</Info>
+
+## Related Capabilities
+
+- [paymasterService](/base-account/reference/core/capabilities/paymasterService) - Combine with sponsored transactions
+- [atomic](/base-account/reference/core/capabilities/atomic) - Use with atomic batch transactions
+
+import PolicyBanner from "/snippets/PolicyBanner.mdx";
+
+<PolicyBanner />

docs/base-account/reference/core/capabilities/overview.mdx

@@ -32,6 +32,7 @@ const baseCapabilities = capabilities["0x2105"]; // Base mainnet chain ID
 | [paymasterService](/base-account/reference/core/capabilities/paymasterService) | `wallet_sendCalls` | Gasless transactions |
 | [flowControl](/base-account/reference/core/capabilities/flowControl) | `wallet_sendCalls` | Flow control |
 | [datacallback](/base-account/reference/core/capabilities/datacallback) | `wallet_sendCalls` | Data callback |
+| [dataSuffix](/base-account/reference/core/capabilities/dataSuffix) | `wallet_sendCalls` | Transaction attribution |
 
 ## Using with wallet_connect
 

docs/base-chain/quickstart/builder-codes.mdx

@@ -33,11 +33,12 @@ Wallet providers need to support the `dataSuffix` capability to enable attributi
 
 <Steps>
   <Step title="Support the dataSuffix Capability">
-    Your wallet should accept a `dataSuffix` string in the `capabilities` object of `wallet_sendCalls`.
+    Your wallet should accept a `dataSuffix` object in the `capabilities` object of `wallet_sendCalls`.
 
     ```typescript lines
-    interface DataSuffixCapability {
-      dataSuffix: string; // hex-encoded bytes provided by the app
+    type DataSuffixCapability = {
+      value: `0x${string}`;  // hex-encoded bytes provided by the app
+      optional?: boolean;    // whether the capability is optional
     }
     ```
 
@@ -53,7 +54,7 @@ Wallet providers need to support the `dataSuffix` capability to enable attributi
         ```typescript lines
         // Minimal example for EOA
         function applySuffixToEOA(tx, capabilities) {
-          const suffix = capabilities.find(c => c.dataSuffix)?.dataSuffix
+          const suffix = capabilities.dataSuffix?.value
           if (!suffix) return tx
 
           return {
@@ -70,7 +71,7 @@ Wallet providers need to support the `dataSuffix` capability to enable attributi
         ```typescript lines
         // Minimal example for ERC-4337
         function applySuffixToUserOp(userOp, capabilities) {
-          const suffix = capabilities.find(c => c.dataSuffix)?.dataSuffix
+          const suffix = capabilities.dataSuffix?.value
           if (!suffix) return userOp
 
           return {

docs/docs.json

@@ -341,7 +341,8 @@
                       "base-account/reference/core/capabilities/flowControl",
                       "base-account/reference/core/capabilities/paymasterService",
                       "base-account/reference/core/capabilities/auxiliaryFunds",
-                      "base-account/reference/core/capabilities/datacallback"
+                      "base-account/reference/core/capabilities/datacallback",
+                      "base-account/reference/core/capabilities/dataSuffix"
                     ]
                   }
                 ]