Upgrade rmcp to 0.8.4 (#6234)

Picks up https://github.com/modelcontextprotocol/rust-sdk/pull/509 which
fixes https://github.com/openai/codex/issues/6164

codex-rs/Cargo.lock

@@ -5010,9 +5010,9 @@ dependencies = [
 
 [[package]]
 name = "rmcp"
-version = "0.8.3"
+version = "0.8.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1fdad1258f7259fdc0f2dfc266939c82c3b5d1fd72bcde274d600cdc27e60243"
+checksum = "a2c66318b30535ccd0d3b39afaa4240d6b5a35328fb7672a28e3386c97472805"
 dependencies = [
  "base64",
  "bytes",
@@ -5044,9 +5044,9 @@ dependencies = [
 
 [[package]]
 name = "rmcp-macros"
-version = "0.8.3"
+version = "0.8.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ede0589a208cc7ce81d1be68aa7e74b917fcd03c81528408bab0457e187dcd9b"
+checksum = "49a19193e0d69bb1c96324b1b4daec078d4c8e76d734e53404c107437858a4d2"
 dependencies = [
  "darling 0.21.3",
  "proc-macro2",

codex-rs/Cargo.toml

@@ -162,7 +162,7 @@ ratatui = "0.29.0"
 ratatui-macros = "0.6.0"
 regex-lite = "0.1.7"
 reqwest = "0.12"
-rmcp = { version = "0.8.3", default-features = false }
+rmcp = { version = "0.8.4", default-features = false }
 schemars = "0.8.22"
 seccompiler = "0.5.0"
 sentry = "0.34.0"
@@ -256,7 +256,12 @@ unwrap_used = "deny"
 # cargo-shear cannot see the platform-specific openssl-sys usage, so we
 # silence the false positive here instead of deleting a real dependency.
 [workspace.metadata.cargo-shear]
-ignored = ["icu_provider", "openssl-sys", "codex-utils-readiness", "codex-utils-tokenizer"]
+ignored = [
+    "icu_provider",
+    "openssl-sys",
+    "codex-utils-readiness",
+    "codex-utils-tokenizer",
+]
 
 [profile.release]
 lto = "fat"

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

@@ -10,9 +10,11 @@ use axum::extract::State;
 use axum::http::Request;
 use axum::http::StatusCode;
 use axum::http::header::AUTHORIZATION;
+use axum::http::header::CONTENT_TYPE;
 use axum::middleware;
 use axum::middleware::Next;
 use axum::response::Response;
+use axum::routing::get;
 use rmcp::ErrorData as McpError;
 use rmcp::handler::server::ServerHandler;
 use rmcp::model::CallToolRequestParam;
@@ -256,14 +258,35 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     };
     eprintln!("starting rmcp streamable http test server on http://{bind_addr}/mcp");
 
-    let router = Router::new().nest_service(
-        "/mcp",
-        StreamableHttpService::new(
-            || Ok(TestToolServer::new()),
-            Arc::new(LocalSessionManager::default()),
-            StreamableHttpServerConfig::default(),
-        ),
-    );
+    let router = Router::new()
+        .route(
+            "/.well-known/oauth-authorization-server/mcp",
+            get({
+                move || async move {
+                    let metadata_base = format!("http://{bind_addr}");
+                    #[expect(clippy::expect_used)]
+                    Response::builder()
+                        .status(StatusCode::OK)
+                        .header(CONTENT_TYPE, "application/json")
+                        .body(Body::from(
+                            serde_json::to_vec(&json!({
+                                "authorization_endpoint": format!("{metadata_base}/oauth/authorize"),
+                                "token_endpoint": format!("{metadata_base}/oauth/token"),
+                                "scopes_supported": [""],
+                            })).expect("failed to serialize metadata"),
+                        ))
+                        .expect("valid metadata response")
+                }
+            }),
+        )
+        .nest_service(
+            "/mcp",
+            StreamableHttpService::new(
+                || Ok(TestToolServer::new()),
+                Arc::new(LocalSessionManager::default()),
+                StreamableHttpServerConfig::default(),
+            ),
+        );
 
     let router = if let Ok(token) = std::env::var("MCP_EXPECT_BEARER") {
         let expected = Arc::new(format!("Bearer {token}"));
@@ -282,6 +305,9 @@ async fn require_bearer(
     request: Request<Body>,
     next: Next,
 ) -> Result<Response, StatusCode> {
+    if request.uri().path().contains("/.well-known/") {
+        return Ok(next.run(request).await);
+    }
     if request
         .headers()
         .get(AUTHORIZATION)