perf(api): SSR-inject system.getLiveNow to cut ~26 req/s off api-primary (#2683)

`system.getLiveNow` is a global boolean (a single `redis.get(LIVE_NOW)`,
identical for every user) fired ambiently on every bootstrap via the
`useIsLive` hook (header logo, social links, social home block). At ~26 req/s
on api-primary it pays the full non-batched tRPC middleware + context-build +
superjson cycle for a boolean — pure per-request fixed CPU cost, the diffuse
lever behind the recurring 504 waves (see datapacket-talos
claudedocs/api-primary-trpc-cost-analysis-2026-06-21.md, Tier-1 #1).

Mirror the proven #2464 SSR-inject pattern: compute the value in
`_app.getInitialProps` (from the SAME already-imported `system-cache` module
that already calls `getBrowsingSettingAddons` — no new client-bundle surface),
thread it through pageProps, and seed it as `initialData` on the fixed
`undefined` query key in AppProvider (alongside the existing getSettings /
getFollowingUsers seeds). The ambient `useIsLive` query then reads a primed
cache and never fires on bootstrap; its own 5-minute refetchInterval keeps it
current once a consumer mounts.

Fail-open to `false` (not-live) in getInitialProps: getLiveNow has no internal
try/catch, and an uncaught redis throw on the SSR path would 500 every render.

Extends tests/preview-ssr-inject.spec.ts with authed + anon describe blocks
asserting (a) the seed is present in __NEXT_DATA__, (b) no system.getLiveNow
request fires on bootstrap, and (c) the seed byte-equals a live authed fetch.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/preview-ssr-inject.spec.ts

@@ -43,6 +43,7 @@ const FEATURE_FLAGS_PROCEDURE = 'user.getFeatureFlags';
 const TOS_PROCEDURE = 'content.checkTosUpdate';
 const ANNOUNCEMENTS_PROCEDURE = 'announcement.getAnnouncements';
 const FOLLOWING_PROCEDURE = 'user.getFollowingUsers';
+const LIVE_NOW_PROCEDURE = 'system.getLiveNow';
 
 // A core page a gate-passing user lands on directly (no /login bounce). Both
 // procedures fire on every logged-in bootstrap regardless of which page, so
@@ -399,6 +400,77 @@ test.describe('SSR-injected getFollowingUsers (logged-in)', () => {
   });
 });
 
+/**
+ * Regression guard for the SSR-inject of `system.getLiveNow` (~26/s on
+ * api-primary). NOT auth-gated — it is a `publicProcedure` consumed by the
+ * ambient `useIsLive` hook (header logo, social links, social home block), so
+ * it fires on every bootstrap, anon and authed alike. SSR-computed in
+ * `_app.getInitialProps` (fail-open to `false`) and seeded in AppProvider on the
+ * fixed `undefined` key. The payload is a plain `boolean` — no Date/array
+ * serialization subtlety, so the seed (JSON) and a live fetch (`result.data.json`)
+ * compare directly. The seed can legitimately be `false` (stream offline); that
+ * is still a valid, present seed and the byte-equality assertion holds.
+ */
+test.describe('SSR-injected getLiveNow (logged-in)', () => {
+  test.use({ storageState: storageStatePath('mod') });
+
+  test('getLiveNow is seeded into __NEXT_DATA__ and not fetched on bootstrap', async ({ page }) => {
+    const trpcUrls = await collectTrpcRequests(page, AUTHED_LANDING);
+
+    const liveNow = await readPageProp(page, 'liveNow');
+    expect(liveNow.present, 'liveNow present in __NEXT_DATA__ pageProps').toBe(true);
+    expect(typeof liveNow.value, 'liveNow seed is a boolean').toBe('boolean');
+
+    const liveNowRequests = trpcUrls.filter((u) => u.includes(LIVE_NOW_PROCEDURE));
+    expect(
+      liveNowRequests,
+      `no ${LIVE_NOW_PROCEDURE} tRPC request should fire on bootstrap (it is SSR-injected); saw:\n${liveNowRequests.join(
+        '\n'
+      )}`
+    ).toHaveLength(0);
+  });
+
+  test('SSR seed byte-equals a live fetch', async ({ page }) => {
+    await page.goto(AUTHED_LANDING, { waitUntil: 'domcontentloaded' });
+
+    const seed = await readPageProp(page, 'liveNow');
+    expect(seed.present, 'liveNow seed present in __NEXT_DATA__').toBe(true);
+
+    const live = await fetchTrpcQueryJson(page, LIVE_NOW_PROCEDURE);
+    expect(
+      seed.value,
+      'system.getLiveNow SSR seed must byte-equal a live resolver fetch'
+    ).toEqual(live);
+    expect(typeof live, 'live getLiveNow is a boolean').toBe('boolean');
+  });
+});
+
+test.describe('SSR-injected getLiveNow (anonymous)', () => {
+  // `system.getLiveNow` is a publicProcedure and fires for anon too, so the seed
+  // must be present on the anon bootstrap as well. No anon "byte-equals a live
+  // fetch" test: the preview-auth gate blocks ALL anonymous /api/trpc/* and
+  // 302-redirects to /login (same reason documented for the anon announcements
+  // case), so an anon live fetch never returns tRPC JSON. The seed-present +
+  // no-bootstrap-fetch contract is what matters and is asserted here.
+  test.use({ storageState: { cookies: [], origins: [] } });
+
+  test('getLiveNow is seeded into __NEXT_DATA__ and not fetched on bootstrap', async ({ page }) => {
+    const trpcUrls = await collectTrpcRequests(page, ANON_LANDING);
+
+    const liveNow = await readPageProp(page, 'liveNow');
+    expect(liveNow.present, 'liveNow present in __NEXT_DATA__ pageProps').toBe(true);
+    expect(typeof liveNow.value, 'liveNow seed is a boolean').toBe('boolean');
+
+    const liveNowRequests = trpcUrls.filter((u) => u.includes(LIVE_NOW_PROCEDURE));
+    expect(
+      liveNowRequests,
+      `no ${LIVE_NOW_PROCEDURE} tRPC request should fire on bootstrap (it is SSR-injected); saw:\n${liveNowRequests.join(
+        '\n'
+      )}`
+    ).toHaveLength(0);
+  });
+});
+
 /**
  * MANUAL CHECKLIST — behaviours of this PR that are not auto-asserted above.
  * (Auth IS supported by this harness, but these are timing/visual/state cases