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

ts/proxies/smart-proxy/models/metrics-types.ts

@@ -72,6 +72,7 @@ export interface IMetrics {
     byBackend(): Map<string, IBackendMetrics>;
     protocols(): Map<string, string>;
     topByErrors(limit?: number): Array<{ backend: string; errors: number }>;
+    detectedProtocols(): IProtocolCacheEntry[];
   };
 
   // UDP metrics
@@ -113,6 +114,26 @@ export interface IMetricsConfig {
   prometheusPrefix: string;        // Default: smartproxy_
 }
 
+/**
+ * Protocol cache entry from the Rust proxy's auto-detection cache.
+ * Shows which protocol (h1/h2/h3) is detected for each backend+domain pair,
+ * including failure suppression state with escalating cooldowns.
+ */
+export interface IProtocolCacheEntry {
+  host: string;
+  port: number;
+  domain: string | null;
+  protocol: string;
+  h3Port: number | null;
+  ageSecs: number;
+  h2Suppressed: boolean;
+  h3Suppressed: boolean;
+  h2CooldownRemainingSecs: number | null;
+  h3CooldownRemainingSecs: number | null;
+  h2ConsecutiveFailures: number | null;
+  h3ConsecutiveFailures: number | null;
+}
+
 /**
  * Per-backend metrics
  */