feat(rustproxy-http): add protocol failure suppression, h3 fallback escalation, and protocol cache metrics exposure

rust/crates/rustproxy/src/lib.rs

@@ -937,8 +937,29 @@ impl RustProxy {
     }
 
     /// Get current metrics snapshot.
+    /// Includes protocol cache entries from the HTTP proxy service.
     pub fn get_metrics(&self) -> Metrics {
-        self.metrics.snapshot()
+        let mut metrics = self.metrics.snapshot();
+        if let Some(ref lm) = self.listener_manager {
+            let entries = lm.http_proxy().protocol_cache_snapshot();
+            metrics.detected_protocols = entries.into_iter().map(|e| {
+                rustproxy_metrics::ProtocolCacheEntryMetric {
+                    host: e.host,
+                    port: e.port,
+                    domain: e.domain,
+                    protocol: e.protocol,
+                    h3_port: e.h3_port,
+                    age_secs: e.age_secs,
+                    h2_suppressed: e.h2_suppressed,
+                    h3_suppressed: e.h3_suppressed,
+                    h2_cooldown_remaining_secs: e.h2_cooldown_remaining_secs,
+                    h3_cooldown_remaining_secs: e.h3_cooldown_remaining_secs,
+                    h2_consecutive_failures: e.h2_consecutive_failures,
+                    h3_consecutive_failures: e.h3_consecutive_failures,
+                }
+            }).collect();
+        }
+        metrics
     }
 
     /// Add a listening port at runtime.