fix(rustproxy-http): validate pooled HTTP/2 connections asynchronously before reuse and evict stale senders

rust/crates/rustproxy-http/src/connection_pool.rs

@@ -10,7 +10,7 @@ use bytes::Bytes;
 use dashmap::DashMap;
 use http_body_util::combinators::BoxBody;
 use hyper::client::conn::{http1, http2};
-use tracing::debug;
+use tracing::{debug, warn};
 
 /// Maximum idle connections per backend key.
 const MAX_IDLE_PER_KEY: usize = 16;
@@ -115,20 +115,27 @@ impl ConnectionPool {
 
     /// Try to get a cloned HTTP/2 sender for the given key.
     /// HTTP/2 senders are Clone-able (multiplexed), so we clone rather than remove.
-    pub fn checkout_h2(&self, key: &PoolKey) -> Option<http2::SendRequest<BoxBody<Bytes, hyper::Error>>> {
+    pub fn checkout_h2(&self, key: &PoolKey) -> Option<(http2::SendRequest<BoxBody<Bytes, hyper::Error>>, Duration)> {
         let entry = self.h2_pool.get(key)?;
         let pooled = entry.value();
+        let age = pooled.created_at.elapsed();
 
         // Check if the h2 connection is still alive and not too old
-        if pooled.sender.is_closed() || pooled.created_at.elapsed() >= MAX_H2_AGE {
+        if pooled.sender.is_closed() || age >= MAX_H2_AGE {
+            let reason = if pooled.sender.is_closed() { "closed" } else { "max_age" };
+            debug!("Pool evict (h2): {}:{} (reason={}, age={:.1}s)", key.host, key.port, reason, age.as_secs_f64());
             drop(entry);
             self.h2_pool.remove(key);
             return None;
         }
 
         if pooled.sender.is_ready() {
-            debug!("Pool hit (h2): {}:{}", key.host, key.port);
-            return Some(pooled.sender.clone());
+            if age > Duration::from_secs(30) {
+                warn!("Pool hit (h2): {}:{} — connection age {:.1}s (>30s, may be stale)", key.host, key.port, age.as_secs_f64());
+            } else {
+                debug!("Pool hit (h2): {}:{} (age={:.1}s)", key.host, key.port, age.as_secs_f64());
+            }
+            return Some((pooled.sender.clone(), age));
         }
         None
     }