Add Cookbook other topics (draft)

docs-src/pages/en/cookbook/e02-sse-event-names.md

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+---
+title: "E02. Use Named Events in SSE"
+order: 48
+status: "draft"
+---
+
+SSE lets you send multiple kinds of events over the same stream. Give each one a name with the `event:` field, and the client can dispatch to a different handler per type. Great for things like "new message", "user joined", "user left" in a chat app.
+
+## Send events with names
+
+```cpp
+auto send_event = [](httplib::DataSink &sink,
+                     const std::string &event,
+                     const std::string &data) {
+  std::string msg = "event: " + event + "\n"
+                  + "data: " + data + "\n\n";
+  sink.write(msg.data(), msg.size());
+};
+
+svr.Get("/chat/stream", [&](const httplib::Request &req, httplib::Response &res) {
+  res.set_chunked_content_provider(
+    "text/event-stream",
+    [&, send_event](size_t offset, httplib::DataSink &sink) {
+      send_event(sink, "message", "Hello!");
+      std::this_thread::sleep_for(std::chrono::seconds(2));
+      send_event(sink, "join", "alice");
+      std::this_thread::sleep_for(std::chrono::seconds(2));
+      send_event(sink, "leave", "bob");
+      std::this_thread::sleep_for(std::chrono::seconds(2));
+      return true;
+    });
+});
+```
+
+A message is `event:` → `data:` → blank line. If you omit `event:`, the client treats it as a default `"message"` event.
+
+## Attach IDs for reconnect
+
+When you include an `id:` field, the client automatically sends it back as `Last-Event-ID` on reconnect, telling the server "here's how far I got."
+
+```cpp
+auto send_event = [](httplib::DataSink &sink,
+                     const std::string &event,
+                     const std::string &data,
+                     const std::string &id) {
+  std::string msg = "id: " + id + "\n"
+                  + "event: " + event + "\n"
+                  + "data: " + data + "\n\n";
+  sink.write(msg.data(), msg.size());
+};
+
+send_event(sink, "message", "Hello!", "42");
+```
+
+The ID format is up to you. Monotonic counters or UUIDs both work — just pick something unique and orderable on the server side. See E03. Handle SSE Reconnection for details.
+
+## JSON payloads in data
+
+For structured data, the usual move is to put JSON in `data:`.
+
+```cpp
+nlohmann::json payload = {
+  {"user", "alice"},
+  {"text", "Hello!"},
+};
+send_event(sink, "message", payload.dump(), "42");
+```
+
+On the client, parse the incoming `data` as JSON to get the original object back.
+
+## Data with newlines
+
+If the data value contains newlines, split it across multiple `data:` lines.
+
+```cpp
+std::string msg = "data: line1\n"
+                  "data: line2\n"
+                  "data: line3\n\n";
+sink.write(msg.data(), msg.size());
+```
+
+On the client side, these come back as a single `data` string with newlines.
+
+> **Note:** Using `event:` makes client-side dispatch cleaner, but it also helps in the browser DevTools — events are easier to filter by type. That matters more than you'd expect while debugging.