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]>

tests/req-telemetry.test.mjs

@@ -0,0 +1,97 @@
+// #9: the cold-login REQ storm's remaining emitters are unpinned, so a
+// dev-gated tracer at the pool.sub choke point aggregates every subscription
+// by kinds + emitting call site. These tests cover the aggregation, the
+// call-site extraction (must skip pool plumbing frames), and that the hot
+// path is a no-op while tracing is off.
+//
+// test_integrity_note:
+//   change_type: ["new_tests"]
+//   scenarios:
+//     - id: SCN-req-trace-aggregation
+//       given: "a telemetry instance with an injected clock and log sink"
+//       when: "subs with various kinds/relay counts are recorded and report() runs"
+//       then: "rows are grouped by kinds+caller, sorted by count, with correct totals and REQ/s"
+//   observable_outcomes:
+//     - "disabled instance records nothing"
+//     - "report() totals equal the recorded subs and relay fan-out"
+//     - "plumbing frames (toolkit/relaySubscriptionService) never become the caller"
+//   determinism_controls:
+//     - "injected now(); no interval timers exercised; synthetic stacks"
+//   anti_cheat_rationale:
+//     prevents: ["hard-coded return value", "over-mocking internal logic"]
+//   relaxation:
+//     did_relax_any_assertion: false
+
+import "./test-helpers/setup-localstorage.mjs";
+import test from "node:test";
+import { strict as assert } from "node:assert";
+import {
+  createReqTelemetry,
+  extractCallSite,
+} from "../js/nostr/reqTelemetry.js";
+
+const STACK = (site) =>
+  [
+    "Error",
+    "    at recordReq (http://x/js/nostr/reqTelemetry.js:180:5)",
+    "    at legacySub (http://x/js/nostr/toolkit.js:529:7)",
+    `    at ${site}`,
+  ].join("\n");
+
+test("records aggregate by kinds + caller and report totals are honest", () => {
+  let t = 0;
+  const logs = [];
+  const telem = createReqTelemetry({
+    now: () => t,
+    log: (payload) => logs.push(payload),
+  });
+  telem.start();
+  t = 0;
+  telem.reset();
+
+  for (let i = 0; i < 3; i += 1) {
+    telem.record(8, [{ kinds: [30000], authors: ["a"] }], STACK("loadLists (http://x/js/subscriptions.js:757:10)"));
+  }
+  telem.record(4, [{ kinds: [0] }, { kinds: [10050] }], STACK("dmBoot (http://x/js/services/dmNostrService.js:127:3)"));
+
+  t = 5000; // 5s window
+  const payload = telem.report({ emit: true });
+
+  assert.equal(payload.totalSubs, 4);
+  assert.equal(payload.totalRelayReqs, 28, "3×8 + 4 relay-level REQs");
+  assert.equal(payload.perSecond, 5.6, "28 REQs over 5s");
+  assert.equal(payload.byKindsAndCaller[0].kinds, "30000");
+  assert.equal(payload.byKindsAndCaller[0].subs, 3);
+  assert.match(payload.byKindsAndCaller[0].caller, /subscriptions\.js:757/);
+  assert.equal(payload.byKindsAndCaller[1].kinds, "0,10050");
+  assert.match(payload.byKindsAndCaller[1].caller, /dmNostrService\.js:127/);
+  assert.equal(logs.length, 1, "report emitted through the injected sink");
+});
+
+test("disabled tracer records nothing; stop() disarms a started one", () => {
+  const telem = createReqTelemetry({ now: () => 0, log: () => {} });
+  telem.record(8, [{ kinds: [30000] }], STACK("x (http://x/js/a.js:1:1)"));
+  assert.equal(telem.report({ emit: false }).totalSubs, 0, "off by default");
+
+  telem.start();
+  telem.record(2, [{ kinds: [7] }], STACK("x (http://x/js/a.js:1:1)"));
+  telem.stop();
+  telem.record(2, [{ kinds: [7] }], STACK("x (http://x/js/a.js:1:1)"));
+  assert.equal(telem.report({ emit: false }).totalSubs, 1, "no records after stop");
+});
+
+test("call-site extraction skips pool plumbing and keeps module:line", () => {
+  assert.match(
+    extractCallSite(STACK("refresh (http://x/js/services/moderationService.js:843:20)")),
+    /moderationService\.js:843/,
+  );
+  // Plumbing-only stack falls back to unknown rather than blaming the shim.
+  assert.equal(
+    extractCallSite(
+      "Error\n    at legacySub (http://x/js/nostr/toolkit.js:529:7)\n    at ensureSubscription (http://x/js/services/relaySubscriptionService.js:158:1)",
+    ),
+    "unknown",
+  );
+  assert.equal(extractCallSite(""), "unknown");
+  assert.equal(extractCallSite(undefined), "unknown");
+});