nostr: dev-gated REQ tracer at the pool.sub choke point (#9)

The cold-login REQ storm's remaining emitters are unpinned (the suspected
per-contact list loops don't exist; mutes are already batched). Every
sub/list flows through the shimmed pool.sub, so recordReq() there aggregates
kinds + relay fan-out + emitting call site per 10s window. Zero-cost when
off; arm with localStorage bitvid:reqTrace=1 (auto in dev mode), read
[req-trace] logs or window.__bitvidReqTrace.report().

One traced cold login on unstable will name the storm's sources; the
batching/deferral pass follows from that data.

Tests: tests/req-telemetry.test.mjs (3).

Co-Authored-By: Claude Fable 5 <[email protected]>

js/nostr/toolkit.js

@@ -3,6 +3,7 @@
 import { isDevMode } from "../config.js";
 import { nostrToolsReady } from "../nostrToolsBootstrap.js";
 import { devLogger, userLogger } from "../utils/logger.js";
+import { recordReq } from "./reqTelemetry.js";
 
 /**
  * The default relay set bitvid bootstraps with before loading a user's
@@ -524,6 +525,10 @@ export function shimLegacySimplePoolMethods(pool) {
       const { relayList, filterList, requests } =
         createLegacySubscriptionContext(relays, filters);
 
+      // #9 REQ tracer: every sub/list passes through here — record kinds,
+      // fan-out, and the emitting call site (no-op unless tracing is armed).
+      recordReq(relayList.length, filterList);
+
       const listeners = {
         event: new Set(),
         eose: new Set(),