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/__tests__/fakeInspectorClient.ts

@@ -33,8 +33,10 @@ import type {
   PromptGetInvocation,
   ResourceReadInvocation,
   ResourceTemplateReadInvocation,
+  ResourceSubscriptionStreamState,
   ToolCallInvocation,
 } from "../types.js";
+import { INACTIVE_SUBSCRIPTION_STREAM_STATE } from "../types.js";
 import type { JsonValue } from "../../json/jsonUtils.js";
 
 type ListResult<TKey extends string, TItem> = {
@@ -249,6 +251,13 @@ export class FakeInspectorClient
     return this.discoverResult;
   }
 
+  resourceSubscriptionStreamState: ResourceSubscriptionStreamState =
+    INACTIVE_SUBSCRIPTION_STREAM_STATE;
+
+  getResourceSubscriptionStreamState(): ResourceSubscriptionStreamState {
+    return this.resourceSubscriptionStreamState;
+  }
+
   getServerSettings(): InspectorServerSettings | undefined {
     return this.serverSettings;
   }