fix(proxy-service): handle HTTP/3 backend forwarding failures with protocol fallback and pool cleanup

changelog.md

@@ -1,5 +1,15 @@
 # Changelog
 
+## Pending
+
+### Fixes
+
+- handle HTTP/3 backend forwarding failures with protocol fallback and pool cleanup (proxy-service)
+  - Retry bodyless requests over HTTP/1.1 when HTTP/3 forwarding fails in auto backend protocol mode
+  - Remove broken HTTP/3 pooled connections and record protocol cache failures to avoid repeated H3 reuse
+  - Add regression coverage for backends that advertise an unavailable Alt-Svc HTTP/3 endpoint
+  - Refresh documentation examples and API notes to reflect target-level load balancing and certificate provisioning event hooks
+
 ## 2026-04-30 - 27.10.0 - feat(exports)
 export datagram handler types and align tests with updated nftables and route security APIs
 
@@ -1207,4 +1217,4 @@ Fix ACME certificate provisioning timing to ensure ports are listening first
 - Fixed race condition where certificate provisioning would start before ports were listening
 - Modified SmartCertManager.initialize() to defer certificate provisioning
 - Added SmartCertManager.provisionCertificatesAfterPortsReady() for delayed provisioning
-- Updated SmartProxy.start() to call certificate provisioning after ports are ready
+- Updated SmartProxy.start() to call certificate provisioning after ports are ready