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.

clients/web/src/test/integration/mcp/remote/remoteClientTransport-unit.test.ts

@@ -562,6 +562,30 @@ describe("RemoteClientTransport (focused branch coverage)", () => {
       ).rejects.toThrow(/Transport is closed/);
     });
 
+    it("does not wait for an SSE response on subscriptions/listen (long-lived stream)", async () => {
+      // A `subscriptions/listen` never yields a JSON-RPC response — only an
+      // acknowledged notification over the event channel — so send() must
+      // resolve promptly instead of hanging on the SSE response wait (#1630).
+      // With a short response timeout, a request that *did* wait would reject.
+      const t = makeTransport(
+        {
+          events: () => openEventsResponse(),
+          send: () => jsonResponse({ ok: true }),
+        },
+        { sseResponseTimeoutMs: 50 },
+      );
+      await t.start();
+      await expect(
+        t.send({
+          jsonrpc: "2.0",
+          id: "listen:0",
+          method: "subscriptions/listen",
+          params: {},
+        }),
+      ).resolves.toBeUndefined();
+      await t.close();
+    });
+
     it("posts a message including relatedRequestId and succeeds", async () => {
       let sentBody: { relatedRequestId?: unknown } | undefined;
       const encoder = new TextEncoder();

clients/web/src/test/integration/mcp/remote/server-extra-coverage.test.ts

@@ -19,7 +19,10 @@ import { join } from "node:path";
 import { serve } from "@hono/node-server";
 import type { ServerType } from "@hono/node-server";
 import type pinoType from "pino";
-import { createRemoteApp } from "@inspector/core/mcp/remote/node/server.js";
+import {
+  createRemoteApp,
+  requestIdForSendWait,
+} from "@inspector/core/mcp/remote/node/server.js";
 import {
   InMemorySecretStore,
   KeychainUnavailableError,
@@ -108,6 +111,34 @@ function makeCapturingLogger(): {
 }
 
 describe("server.ts supplemental coverage", () => {
+  describe("requestIdForSendWait (#1630)", () => {
+    it("returns the id for an ordinary request", () => {
+      expect(
+        requestIdForSendWait({ jsonrpc: "2.0", id: 7, method: "tools/list" }),
+      ).toBe(7);
+    });
+
+    it("does not wait for a response on subscriptions/listen (long-lived stream)", () => {
+      expect(
+        requestIdForSendWait({
+          jsonrpc: "2.0",
+          id: "listen:0",
+          method: "subscriptions/listen",
+          params: {},
+        }),
+      ).toBeUndefined();
+    });
+
+    it("returns undefined for a notification (no id)", () => {
+      expect(
+        requestIdForSendWait({
+          jsonrpc: "2.0",
+          method: "notifications/initialized",
+        }),
+      ).toBeUndefined();
+    });
+  });
+
   describe("/api/log forwardLogEvent shapes", () => {
     let h: Harness;
     let records: Array<{ level: string; args: unknown[] }>;