Fix/issue 817 idle timeout log level (#824)

* fix(transport): downgrade idle timeout log from error to debug

Idle keep-alive timeout is normal zombie-session cleanup, not a transport failure.

Route it through a dedicated WorkerQuitReason::IdleTimeout variant.

Log it at debug level instead of treating it as a fatal error.

Remove the unused LocalSessionWorkerError::KeepAliveTimeout variant.

Closes #817

* fix(session): tolerate dead worker in close_session

Swallow SessionServiceTerminated in close_session when the worker has already exited.
This prevents a spurious ERROR log during the post-exit cleanup path in
spawn_session_worker.

* fix(transport): address PR review feedback

- deprecate KeepAliveTimeout
- harden tests

crates/rmcp/src/transport/streamable_http_server/session/local.rs

@@ -66,9 +66,16 @@ impl SessionManager for LocalSessionManager {
         Ok(response)
     }
     async fn close_session(&self, id: &SessionId) -> Result<(), Self::Error> {
-        let mut sessions = self.sessions.write().await;
-        if let Some(handle) = sessions.remove(id) {
-            handle.close().await?;
+        let handle = {
+            let mut sessions = self.sessions.write().await;
+            sessions.remove(id)
+        };
+        if let Some(handle) = handle {
+            match handle.close().await {
+                // Worker already exited — nothing left to clean up.
+                Ok(()) | Err(SessionError::SessionServiceTerminated) => {}
+                Err(e) => return Err(e.into()),
+            }
         }
         Ok(())
     }
@@ -928,6 +935,7 @@ pub enum LocalSessionWorkerError {
     FailToSendInitializeRequest(SessionError),
     #[error("fail to handle message: {0}")]
     FailToHandleMessage(SessionError),
+    #[deprecated(note = "idle timeout now surfaces as WorkerQuitReason::IdleTimeout")]
     #[error("keep alive timeout after {}ms", _0.as_millis())]
     KeepAliveTimeout(Duration),
     #[error("init timeout after {}ms", _0.as_millis())]
@@ -1021,7 +1029,7 @@ impl Worker for LocalSessionWorker {
                     return Err(WorkerQuitReason::Cancelled)
                 }
                 _ = keep_alive_timeout => {
-                    return Err(WorkerQuitReason::fatal(LocalSessionWorkerError::KeepAliveTimeout(keep_alive), "poll next session event"))
+                    return Err(WorkerQuitReason::IdleTimeout(keep_alive))
                 }
             };
             match event {

crates/rmcp/src/transport/worker.rs

@@ -1,4 +1,4 @@
-use std::borrow::Cow;
+use std::{borrow::Cow, time::Duration};
 
 use tokio_util::sync::CancellationToken;
 use tracing::{Instrument, Level};
@@ -22,6 +22,8 @@ pub enum WorkerQuitReason<E> {
     TransportClosed,
     #[error("Handler terminated")]
     HandlerTerminated,
+    #[error("Worker idle timeout after {}ms", _0.as_millis())]
+    IdleTimeout(Duration),
 }
 
 impl<E: std::error::Error + Send + 'static> WorkerQuitReason<E> {
@@ -122,7 +124,8 @@ impl<W: Worker> WorkerTransport<W> {
                 .inspect_err(|e| match e {
                     WorkerQuitReason::Cancelled
                     | WorkerQuitReason::TransportClosed
-                    | WorkerQuitReason::HandlerTerminated => {
+                    | WorkerQuitReason::HandlerTerminated
+                    | WorkerQuitReason::IdleTimeout(_) => {
                         tracing::debug!("worker quit with reason: {:?}", e);
                     }
                     WorkerQuitReason::Join(e) => {