Bump version to 0.10.3 and add r402-mcp crate for Model Context Protocol payment integration

* Bump workspace version from 0.10.2 to 0.10.3 in Cargo.toml
* Add r402-mcp to workspace members and publish workflow package list
* Add r402-mcp workspace dependency and rmcp dependency for MCP protocol support
* Create r402-mcp crate with client-side auto-payment and server-side payment wrapper for MCP tools
* Implement X402McpClient with automatic 402 payment handling, scheme client integration, and lifecycle

Author: gitctrlx

.github/workflows/rust-publish.yml

@@ -12,6 +12,6 @@ jobs:
   call-publish:
     uses: qntx/workflows/.github/workflows/rust-publish.yml@main
     with:
-      package: "r402 r402-evm r402-svm r402-http"
+      package: "r402 r402-evm r402-svm r402-http r402-mcp"
     secrets:
       CARGO_REGISTRY_TOKEN: ${{ secrets.CARGO_REGISTRY_TOKEN }}

Cargo.lock

@@ -1,10 +1,10 @@
 [workspace]
-members = ["r402", "r402-evm", "r402-http", "r402-svm"]
+members = ["r402", "r402-evm", "r402-http", "r402-mcp", "r402-svm"]
 default-members = ["r402"]
 resolver = "3"
 
 [workspace.package]
-version = "0.10.2"
+version = "0.10.3"
 edition = "2024"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/qntx/r402"
@@ -15,6 +15,7 @@ description = "x402 Payment Protocol SDK for Rust."
 r402 = { version = "0.10", path = "r402" }
 r402-evm = { version = "0.10", path = "r402-evm" }
 r402-http = { version = "0.10", path = "r402-http" }
+r402-mcp = { version = "0.10", path = "r402-mcp" }
 r402-svm = { version = "0.10", path = "r402-svm" }
 
 # Core
@@ -73,6 +74,9 @@ solana-transaction = "3"
 spl-token = { version = "9", features = ["no-entrypoint"] }
 spl-token-2022 = { version = "10", features = ["no-entrypoint"] }
 
+# MCP
+rmcp = { version = "0.15", default-features = false, features = ["client", "server", "schemars"] }
+
 # Telemetry
 tracing = "0.1"
 tracing-core = "0.1"

Cargo.toml

@@ -252,9 +252,7 @@ where
         })
     }
 
-    fn supported(
-        &self,
-    ) -> BoxFuture<'_, Result<proto::SupportedResponse, FacilitatorError>> {
+    fn supported(&self) -> BoxFuture<'_, Result<proto::SupportedResponse, FacilitatorError>> {
         Box::pin(async move {
             let chain_id = self.provider.chain_id();
             let kinds = vec![proto::SupportedPaymentKind {

r402-evm/src/exact/facilitator/mod.rs

@@ -154,9 +154,7 @@ impl Facilitator for FacilitatorClient {
         })
     }
 
-    fn supported(
-        &self,
-    ) -> BoxFuture<'_, Result<SupportedResponse, FacilitatorError>> {
+    fn supported(&self) -> BoxFuture<'_, Result<SupportedResponse, FacilitatorError>> {
         Box::pin(async move {
             Self::supported(self)
                 .await

r402-http/src/server/facilitator.rs

@@ -0,0 +1,25 @@
+[package]
+name = "r402-mcp"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+description = "MCP (Model Context Protocol) integration for the x402 payment protocol."
+
+[dependencies]
+r402 = { workspace = true }
+serde = { workspace = true }
+serde_json = { workspace = true }
+thiserror = { workspace = true }
+
+# Optional
+rmcp = { workspace = true, optional = true }
+tracing = { workspace = true, optional = true }
+
+[features]
+default = []
+rmcp = ["dep:rmcp"]
+telemetry = ["dep:tracing"]
+
+[lints]
+workspace = true

r402-mcp/Cargo.toml

@@ -0,0 +1,101 @@
+# r402-mcp
+
+MCP (Model Context Protocol) integration for the x402 payment protocol.
+
+This crate enables paid tool calls in MCP servers and automatic payment handling in MCP clients, following the [x402 payment protocol](https://github.com/coinbase/x402) specification.
+
+## Features
+
+- **Client-side auto-payment** — `X402McpClient` wraps any MCP caller with automatic 402 payment handling
+- **Server-side payment wrapper** — `PaymentWrapper` wraps tool handlers with verify → execute → settle lifecycle
+- **Framework-agnostic** — Works with any MCP SDK via the `McpCaller` trait and `serde_json::Value`-based types
+- **Lifecycle hooks** — Trait-based hooks for both client and server sides
+- **Payment extraction utilities** — Extract/attach payment data from/to MCP `_meta` fields
+
+## Architecture
+
+The crate follows the x402 MCP specification where payment data flows through JSON-RPC `_meta` fields:
+
+- `_meta["x402/payment"]` — Client → Server: payment payload
+- `_meta["x402/payment-response"]` — Server → Client: settlement response
+
+### Client Flow
+
+1. Call tool without payment
+2. If 402: extract `PaymentRequired` from `structuredContent` or `content[0].text`
+3. Create payment via registered `SchemeClient`s
+4. Retry with payment in `_meta["x402/payment"]`
+5. Extract settlement response from result `_meta`
+
+### Server Flow
+
+1. Extract `x402/payment` from request `_meta`
+2. If missing → return 402 error with `PaymentRequired`
+3. Verify payment via `Facilitator`
+4. Execute original handler
+5. Settle payment via `Facilitator`
+6. Attach `SettleResponse` to result `_meta`
+
+## Usage
+
+### Client
+
+```rust,ignore
+use r402_mcp::client::{X402McpClient, McpCaller};
+use r402_mcp::types::ClientOptions;
+
+let client = X402McpClient::builder(my_mcp_session)
+    .scheme_client(Box::new(evm_scheme_client))
+    .auto_payment(true)
+    .build();
+
+let result = client.call_tool("get_weather", args).await?;
+if let Some(settle) = &result.payment_response {
+    println!("Paid! tx: {:?}", settle);
+}
+```
+
+### Server
+
+```rust,ignore
+use r402_mcp::server::PaymentWrapper;
+use r402_mcp::types::PaymentWrapperConfig;
+
+let wrapper = PaymentWrapper::new(facilitator.into(), PaymentWrapperConfig {
+    accepts: vec![payment_requirements],
+    resource: Some(resource_info),
+    ..Default::default()
+});
+
+let result = wrapper.process(request, |req| async {
+    Ok(CallToolResult {
+        content: vec![ContentItem::text("Weather: sunny")],
+        ..Default::default()
+    })
+}).await;
+```
+
+### Low-level Utilities
+
+```rust
+use r402_mcp::extract;
+
+// Extract payment from meta
+let payment = extract::extract_payment_from_meta(&meta);
+
+// Attach payment to meta
+extract::attach_payment_to_meta(&mut meta, payment_value);
+
+// Extract payment required from error result
+let pr = extract::extract_payment_required_from_result(&result);
+```
+
+## Feature Flags
+
+| Feature | Description |
+|---------|-------------|
+| `telemetry` | Enables `tracing` instrumentation |
+
+## License
+
+Licensed under either of [Apache License, Version 2.0](../LICENSE-APACHE) or [MIT license](../LICENSE-MIT) at your option.