Resources: subscriptions/listen model on modern servers (era fork) (#1630) (#1730)

Fork resource subscriptions by protocol era: legacy keeps resources/subscribe; modern (2026-07-28) models subscriptions as a filter over one long-lived subscriptions/listen stream with reconnect-by-re-listen (capped backoff), an optimistic Connecting→Listening header badge, and a fix so the browser proxy no longer blocks listen() ~60s. Closes #1630.

core/mcp/inspectorClientProtocol.ts

@@ -19,6 +19,7 @@ import type {
   ResourceTemplateReadInvocation,
   PromptGetInvocation,
   ToolCallInvocation,
+  ResourceSubscriptionStreamState,
 } from "./types.js";
 import type {
   CacheMode,
@@ -60,6 +61,7 @@ export interface InspectorClientProtocol extends InspectorClientEventTarget {
   getInstructions(): string | undefined;
   getProtocolVersion(): string | undefined;
   getProtocolEra(): ProtocolEra | undefined;
+  getResourceSubscriptionStreamState(): ResourceSubscriptionStreamState;
   getDiscoverResult(): DiscoverResult | undefined;
   getServerSettings(): InspectorServerSettings | undefined;
   setServerSettings(settings: InspectorServerSettings): void;