[MCP] Add support for resources (#5239)

This PR adds support for [MCP
resources](https://modelcontextprotocol.io/specification/2025-06-18/server/resources)
by adding three new tools for the model:
1. `list_resources`
2. `list_resource_templates`
3. `read_resource`

These 3 tools correspond to the [three primary MCP resource protocol
messages](https://modelcontextprotocol.io/specification/2025-06-18/server/resources#protocol-messages).

Example of listing and reading a GitHub resource tempalte
<img width="2984" height="804" alt="CleanShot 2025-10-15 at 17 31 10"
src="https://github.com/user-attachments/assets/89b7f215-2e2a-41c5-90dd-b932ac84a585"
/>

`/mcp` with Figma configured
<img width="2984" height="442" alt="CleanShot 2025-10-15 at 18 29 35"
src="https://github.com/user-attachments/assets/a7578080-2ed2-4c59-b9b4-d8461f90d8ee"
/>

Fixes #4956

codex-rs/rmcp-client/src/bin/test_streamable_http_server.rs

@@ -18,8 +18,17 @@ use rmcp::handler::server::ServerHandler;
 use rmcp::model::CallToolRequestParam;
 use rmcp::model::CallToolResult;
 use rmcp::model::JsonObject;
+use rmcp::model::ListResourceTemplatesResult;
+use rmcp::model::ListResourcesResult;
 use rmcp::model::ListToolsResult;
 use rmcp::model::PaginatedRequestParam;
+use rmcp::model::RawResource;
+use rmcp::model::RawResourceTemplate;
+use rmcp::model::ReadResourceRequestParam;
+use rmcp::model::ReadResourceResult;
+use rmcp::model::Resource;
+use rmcp::model::ResourceContents;
+use rmcp::model::ResourceTemplate;
 use rmcp::model::ServerCapabilities;
 use rmcp::model::ServerInfo;
 use rmcp::model::Tool;
@@ -33,13 +42,22 @@ use tokio::task;
 #[derive(Clone)]
 struct TestToolServer {
     tools: Arc<Vec<Tool>>,
+    resources: Arc<Vec<Resource>>,
+    resource_templates: Arc<Vec<ResourceTemplate>>,
 }
 
+const MEMO_URI: &str = "memo://codex/example-note";
+const MEMO_CONTENT: &str = "This is a sample MCP resource served by the rmcp test server.";
+
 impl TestToolServer {
     fn new() -> Self {
         let tools = vec![Self::echo_tool()];
+        let resources = vec![Self::memo_resource()];
+        let resource_templates = vec![Self::memo_template()];
         Self {
             tools: Arc::new(tools),
+            resources: Arc::new(resources),
+            resource_templates: Arc::new(resource_templates),
         }
     }
 
@@ -62,6 +80,36 @@ impl TestToolServer {
             Arc::new(schema),
         )
     }
+
+    fn memo_resource() -> Resource {
+        let raw = RawResource {
+            uri: MEMO_URI.to_string(),
+            name: "example-note".to_string(),
+            title: Some("Example Note".to_string()),
+            description: Some("A sample MCP resource exposed for integration tests.".to_string()),
+            mime_type: Some("text/plain".to_string()),
+            size: None,
+            icons: None,
+        };
+        Resource::new(raw, None)
+    }
+
+    fn memo_template() -> ResourceTemplate {
+        let raw = RawResourceTemplate {
+            uri_template: "memo://codex/{slug}".to_string(),
+            name: "codex-memo".to_string(),
+            title: Some("Codex Memo".to_string()),
+            description: Some(
+                "Template for memo://codex/{slug} resources used in tests.".to_string(),
+            ),
+            mime_type: Some("text/plain".to_string()),
+        };
+        ResourceTemplate::new(raw, None)
+    }
+
+    fn memo_text() -> &'static str {
+        MEMO_CONTENT
+    }
 }
 
 #[derive(Deserialize)]
@@ -77,6 +125,7 @@ impl ServerHandler for TestToolServer {
             capabilities: ServerCapabilities::builder()
                 .enable_tools()
                 .enable_tool_list_changed()
+                .enable_resources()
                 .build(),
             ..ServerInfo::default()
         }
@@ -96,6 +145,53 @@ impl ServerHandler for TestToolServer {
         }
     }
 
+    fn list_resources(
+        &self,
+        _request: Option<PaginatedRequestParam>,
+        _context: rmcp::service::RequestContext<rmcp::service::RoleServer>,
+    ) -> impl std::future::Future<Output = Result<ListResourcesResult, McpError>> + Send + '_ {
+        let resources = self.resources.clone();
+        async move {
+            Ok(ListResourcesResult {
+                resources: (*resources).clone(),
+                next_cursor: None,
+            })
+        }
+    }
+
+    async fn list_resource_templates(
+        &self,
+        _request: Option<PaginatedRequestParam>,
+        _context: rmcp::service::RequestContext<rmcp::service::RoleServer>,
+    ) -> Result<ListResourceTemplatesResult, McpError> {
+        Ok(ListResourceTemplatesResult {
+            resource_templates: (*self.resource_templates).clone(),
+            next_cursor: None,
+        })
+    }
+
+    async fn read_resource(
+        &self,
+        ReadResourceRequestParam { uri }: ReadResourceRequestParam,
+        _context: rmcp::service::RequestContext<rmcp::service::RoleServer>,
+    ) -> Result<ReadResourceResult, McpError> {
+        if uri == MEMO_URI {
+            Ok(ReadResourceResult {
+                contents: vec![ResourceContents::TextResourceContents {
+                    uri,
+                    mime_type: Some("text/plain".to_string()),
+                    text: Self::memo_text().to_string(),
+                    meta: None,
+                }],
+            })
+        } else {
+            Err(McpError::resource_not_found(
+                "resource_not_found",
+                Some(json!({ "uri": uri })),
+            ))
+        }
+    }
+
     async fn call_tool(
         &self,
         request: CallToolRequestParam,