querylog: the writer queue defaults to 1024 entries, and a live stream allocates its ring on subscribe instead of at boot

src/app.zig

@@ -584,16 +584,10 @@ fn serve(r: cli.Runner, args: cli.RunArgs) !u8 {
 
     // Milestone 8 fans every logged query out to the SSE hub as well. The hub
     // exists only when the web interface does (ruling 6) — without it the sink
-    // costs the query path one null check. Its rings are ~900 KiB, so it lives
-    // on the heap and initializes in place; a by-value init would copy the
-    // whole of it through this frame.
-    var hub: ?*sse.Hub = null;
-    defer if (hub) |hub_ptr| gpa.destroy(hub_ptr);
-    if (cfg.web.enabled) {
-        const created = try gpa.create(sse.Hub);
-        created.init();
-        hub = created;
-    }
+    // costs the query path one null check.
+    var hub_storage: sse.Hub = .init(gpa);
+    defer hub_storage.deinit();
+    const hub: ?*sse.Hub = if (cfg.web.enabled) &hub_storage else null;
 
     // -----------------------------------------------------------------------
     // disk, retention and the remaining connections (ruling 21)