[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/tests/resources.rs

@@ -0,0 +1,124 @@
+use std::ffi::OsString;
+use std::path::PathBuf;
+use std::time::Duration;
+
+use codex_rmcp_client::RmcpClient;
+use escargot::CargoBuild;
+use mcp_types::ClientCapabilities;
+use mcp_types::Implementation;
+use mcp_types::InitializeRequestParams;
+use mcp_types::ListResourceTemplatesResult;
+use mcp_types::ReadResourceRequestParams;
+use mcp_types::ReadResourceResultContents;
+use mcp_types::Resource;
+use mcp_types::ResourceTemplate;
+use mcp_types::TextResourceContents;
+use serde_json::json;
+
+const RESOURCE_URI: &str = "memo://codex/example-note";
+
+fn stdio_server_bin() -> anyhow::Result<PathBuf> {
+    let build = CargoBuild::new()
+        .package("codex-rmcp-client")
+        .bin("test_stdio_server")
+        .run()?;
+    Ok(build.path().to_path_buf())
+}
+
+fn init_params() -> InitializeRequestParams {
+    InitializeRequestParams {
+        capabilities: ClientCapabilities {
+            experimental: None,
+            roots: None,
+            sampling: None,
+            elicitation: Some(json!({})),
+        },
+        client_info: Implementation {
+            name: "codex-test".into(),
+            version: "0.0.0-test".into(),
+            title: Some("Codex rmcp resource test".into()),
+            user_agent: None,
+        },
+        protocol_version: mcp_types::MCP_SCHEMA_VERSION.to_string(),
+    }
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+async fn rmcp_client_can_list_and_read_resources() -> anyhow::Result<()> {
+    let client = RmcpClient::new_stdio_client(
+        stdio_server_bin()?.into(),
+        Vec::<OsString>::new(),
+        None,
+        &[],
+        None,
+    )
+    .await?;
+
+    client
+        .initialize(init_params(), Some(Duration::from_secs(5)))
+        .await?;
+
+    let list = client
+        .list_resources(None, Some(Duration::from_secs(5)))
+        .await?;
+    let memo = list
+        .resources
+        .iter()
+        .find(|resource| resource.uri == RESOURCE_URI)
+        .expect("memo resource present");
+    assert_eq!(
+        memo,
+        &Resource {
+            annotations: None,
+            description: Some("A sample MCP resource exposed for integration tests.".to_string()),
+            mime_type: Some("text/plain".to_string()),
+            name: "example-note".to_string(),
+            size: None,
+            title: Some("Example Note".to_string()),
+            uri: RESOURCE_URI.to_string(),
+        }
+    );
+    let templates = client
+        .list_resource_templates(None, Some(Duration::from_secs(5)))
+        .await?;
+    assert_eq!(
+        templates,
+        ListResourceTemplatesResult {
+            next_cursor: None,
+            resource_templates: vec![ResourceTemplate {
+                annotations: None,
+                description: Some(
+                    "Template for memo://codex/{slug} resources used in tests.".to_string()
+                ),
+                mime_type: Some("text/plain".to_string()),
+                name: "codex-memo".to_string(),
+                title: Some("Codex Memo".to_string()),
+                uri_template: "memo://codex/{slug}".to_string(),
+            }],
+        }
+    );
+
+    let read = client
+        .read_resource(
+            ReadResourceRequestParams {
+                uri: RESOURCE_URI.to_string(),
+            },
+            Some(Duration::from_secs(5)),
+        )
+        .await?;
+    let ReadResourceResultContents::TextResourceContents(text) =
+        read.contents.first().expect("resource contents present")
+    else {
+        panic!("expected text resource");
+    };
+    assert_eq!(
+        text,
+        &TextResourceContents {
+            text: "This is a sample MCP resource served by the rmcp test server.".to_string(),
+            uri: RESOURCE_URI.to_string(),
+            mime_type: Some("text/plain".to_string()),
+        }
+    );
+
+    Ok(())
+}