Bump runtimed to include iopub_welcome (JEP 65) support (#72)

Pull in latest runtimed changes that add XPUB socket support and iopub_welcome
messages for improved IOPub reliability. Update kernel-testbed to use the new
wait_for_iopub_welcome() API and add a conformance test for JEP 65 compliance.

Changes:
- cargo update: runtimed commits d703acca -> 302c4a2b
- Replace 100ms settle time with wait_for_iopub_welcome() (500ms timeout)
- Add iopub_welcome_received tracking to KernelUnderTest
- Add Tier 1 conformance test for iopub_welcome (JEP 65)

Author: rgbkrk

Cargo.lock

@@ -13,8 +13,8 @@ use runtimelib::{
     create_client_control_connection, create_client_heartbeat_connection,
     create_client_iopub_connection, create_client_shell_connection_with_identity,
     create_client_stdin_connection_with_identity, peer_identity_for_session, peek_ports,
-    ClientControlConnection, ClientHeartbeatConnection, ClientIoPubConnection,
-    ClientShellConnection, ClientStdinConnection, KernelspecDir,
+    wait_for_iopub_welcome, ClientControlConnection, ClientHeartbeatConnection,
+    ClientIoPubConnection, ClientShellConnection, ClientStdinConnection, KernelspecDir,
 };
 use std::net::{IpAddr, Ipv4Addr};
 use std::path::PathBuf;
@@ -24,8 +24,9 @@ use thiserror::Error;
 use tokio::process::Child;
 use tokio::time::timeout;
 
-/// Time to wait for IOPub to settle after connecting
-const IOPUB_SETTLE_TIME: Duration = Duration::from_millis(100);
+/// Timeout for waiting for iopub_welcome message (JEP 65)
+/// Kernels using XPUB sockets will send this immediately, others will timeout gracefully
+const IOPUB_WELCOME_TIMEOUT: Duration = Duration::from_millis(500);
 
 #[derive(Error, Debug)]
 pub enum HarnessError {
@@ -72,6 +73,8 @@ pub struct KernelUnderTest {
     snippets: LanguageSnippets,
     /// Per-test timeout
     test_timeout: Duration,
+    /// Whether iopub_welcome was received (JEP 65 support)
+    iopub_welcome_received: bool,
 }
 
 impl KernelUnderTest {
@@ -128,7 +131,7 @@ impl KernelUnderTest {
         .await
         .map_err(|e| HarnessError::ConnectionFailed(e.to_string()))?;
 
-        let iopub = create_client_iopub_connection(&connection_info, "", &session_id)
+        let mut iopub = create_client_iopub_connection(&connection_info, "", &session_id)
             .await
             .map_err(|e| HarnessError::ConnectionFailed(e.to_string()))?;
 
@@ -145,8 +148,13 @@ impl KernelUnderTest {
             .await
             .map_err(|e| HarnessError::ConnectionFailed(e.to_string()))?;
 
-        // Wait for IOPub to settle
-        tokio::time::sleep(IOPUB_SETTLE_TIME).await;
+        // Wait for iopub_welcome (JEP 65) or timeout gracefully for legacy kernels
+        let iopub_welcome_received =
+            match wait_for_iopub_welcome(&mut iopub, IOPUB_WELCOME_TIMEOUT).await {
+                Ok(Some(_subscription)) => true,
+                Ok(None) => false, // Timeout or non-welcome message - kernel doesn't support XPUB
+                Err(_) => false,   // Error during wait - proceed anyway
+            };
 
         // Default snippets (will be updated after kernel_info)
         let snippets = LanguageSnippets::for_language("python");
@@ -164,6 +172,7 @@ impl KernelUnderTest {
             kernel_info: None,
             snippets,
             test_timeout,
+            iopub_welcome_received,
         };
 
         // Get kernel info to determine language
@@ -208,6 +217,11 @@ impl KernelUnderTest {
         &self.snippets
     }
 
+    /// Check if iopub_welcome was received (JEP 65 support).
+    pub fn iopub_welcome_received(&self) -> bool {
+        self.iopub_welcome_received
+    }
+
     /// Send a request on shell and wait for reply.
     pub async fn shell_request(
         &mut self,

src/harness.rs

@@ -30,6 +30,23 @@ fn test_heartbeat_responds(
     })
 }
 
+fn test_iopub_welcome(
+    kernel: &mut KernelUnderTest,
+) -> Pin<Box<dyn Future<Output = TestResult> + Send + '_>> {
+    Box::pin(async move {
+        if kernel.iopub_welcome_received() {
+            TestResult::Pass
+        } else {
+            // iopub_welcome is optional (JEP 65) - kernels using legacy PUB sockets won't send it
+            TestResult::PartialPass {
+                score: 0.5,
+                notes: "No iopub_welcome received (kernel may use legacy PUB socket instead of XPUB)"
+                    .to_string(),
+            }
+        }
+    })
+}
+
 fn test_kernel_info_reply_valid(
     kernel: &mut KernelUnderTest,
 ) -> Pin<Box<dyn Future<Output = TestResult> + Send + '_>> {
@@ -880,6 +897,13 @@ pub fn all_tests() -> Vec<ConformanceTest> {
             message_type: "heartbeat",
             run: test_heartbeat_responds,
         },
+        ConformanceTest {
+            name: "iopub_welcome",
+            category: TestCategory::Tier1Basic,
+            description: "Kernel sends iopub_welcome on XPUB subscription (JEP 65)",
+            message_type: "iopub_welcome",
+            run: test_iopub_welcome,
+        },
         ConformanceTest {
             name: "kernel_info_reply_valid",
             category: TestCategory::Tier1Basic,