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/components/elements/SubscriptionStreamBadge/subscriptionStreamUtils.ts

@@ -0,0 +1,53 @@
+import type { ResourceSubscriptionStreamStatus } from "../../../../../../core/mcp/types.js";
+
+export interface StreamPresentation {
+  /** Mantine palette color name conveying the status. */
+  color: string;
+  /** Short label shown on the panel badge. */
+  label: string;
+  /** Full explanation shown in the tooltip (both variants). */
+  tooltip: string;
+}
+
+const STREAM_INTRO =
+  "On modern (2026-07-28) servers, resource subscriptions are a filter over one long-lived subscriptions/listen stream.";
+
+// Keyed by status so it's exhaustive at compile time: a new
+// `ResourceSubscriptionStreamStatus` that isn't handled here is a type error
+// (no unreachable `default` needed, so it stays fully covered).
+const PRESENTATION: Record<
+  ResourceSubscriptionStreamStatus,
+  StreamPresentation
+> = {
+  connecting: {
+    color: "blue",
+    label: "Connecting…",
+    tooltip: `${STREAM_INTRO} Opening the stream — waiting for the server to acknowledge the subscription.`,
+  },
+  acknowledged: {
+    color: "green",
+    label: "Listening",
+    tooltip: `${STREAM_INTRO} The server acknowledged the subscription and the stream is open, carrying resources/updated notifications.`,
+  },
+  reconnecting: {
+    color: "yellow",
+    label: "Reconnecting…",
+    tooltip: `${STREAM_INTRO} The stream dropped unexpectedly; re-listening to re-establish it (there is no resumability, so the full filter is re-sent).`,
+  },
+  ended: {
+    color: "gray",
+    label: "Stream ended",
+    tooltip: `${STREAM_INTRO} The stream is closed and won't reconnect on its own — either the server ended it (for example, on shutdown) or reconnection was abandoned after repeated failures. Re-subscribe to try again.`,
+  },
+};
+
+/**
+ * Maps a modern listen-stream status to its badge color, label, and tooltip
+ * copy (#1630). Kept in its own module so the badge component file exports only
+ * a component (react-refresh rule).
+ */
+export function subscriptionStreamPresentation(
+  status: ResourceSubscriptionStreamStatus,
+): StreamPresentation {
+  return PRESENTATION[status];
+}