Realtime KDS via Server-Sent Events

Replace the kitchen display's 4s polling with a pushed feed. GET /kitchen/stream
holds an SSE connection and emits the board the moment it changes (~1s tick,
heartbeat between changes), so fired/bumped/guest orders land on screen near
instantly. Bounded to ~25s per connection so PHP-FPM workers recycle — the
browser's EventSource reconnects automatically; if EventSource is unavailable it
falls back to polling /kitchen/feed. Sends X-Accel-Buffering: no so nginx streams
it, and releases the session early (DB sessions don't lock, but be safe).

feed()/stream() now share buildTickets(); behaviour of the JSON feed (initial
load + fallback) is unchanged. Suite green (12).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/Http/Controllers/Pos/KitchenController.php

@@ -9,7 +9,9 @@ use App\Models\PosSaleLine;
 use App\Models\PosStation;
 use Illuminate\Http\JsonResponse;
 use Illuminate\Http\Request;
+use Illuminate\Support\Collection;
 use Illuminate\View\View;
+use Symfony\Component\HttpFoundation\StreamedResponse;
 
 class KitchenController extends Controller
 {
@@ -24,11 +26,70 @@ class KitchenController extends Controller
 
     /**
      * Active kitchen tickets — open sales with fired-but-not-served lines.
+     * Used for the initial load and as a fallback when SSE is unavailable.
      */
     public function feed(Request $request): JsonResponse
     {
-        $owner = $this->ownerRef($request);
+        return response()->json($this->payload($this->ownerRef($request)));
+    }
 
+    /**
+     * Realtime feed over Server-Sent Events. Pushes the board whenever it
+     * changes (~1s tick), with a heartbeat. Bounded lifetime so PHP-FPM workers
+     * recycle — the browser's EventSource reconnects automatically.
+     */
+    public function stream(Request $request): StreamedResponse
+    {
+        $owner = $this->ownerRef($request);
+        // Release the session lock early (DB driver doesn't lock, but be safe).
+        $request->session()->save();
+
+        $response = new StreamedResponse(function () use ($owner) {
+            while (ob_get_level() > 0) {
+                @ob_end_flush();
+            }
+            @set_time_limit(0);
+
+            $start = time();
+            $lastHash = null;
+
+            while (true) {
+                $payload = $this->payload($owner);
+                $json = json_encode($payload);
+                $hash = md5((string) $json);
+
+                if ($hash !== $lastHash) {
+                    echo 'data: '.$json."\n\n";
+                    $lastHash = $hash;
+                } else {
+                    echo ": ping\n\n"; // heartbeat
+                }
+                @ob_flush();
+                @flush();
+
+                if (connection_aborted() || (time() - $start) >= 25) {
+                    break;
+                }
+                sleep(1);
+            }
+        });
+
+        $response->headers->set('Content-Type', 'text/event-stream');
+        $response->headers->set('Cache-Control', 'no-cache');
+        $response->headers->set('Connection', 'keep-alive');
+        $response->headers->set('X-Accel-Buffering', 'no'); // disable nginx buffering
+
+        return $response;
+    }
+
+    /** @return array{tickets: \Illuminate\Support\Collection, server_time: string} */
+    private function payload(string $owner): array
+    {
+        return ['tickets' => $this->buildTickets($owner), 'server_time' => now()->toIso8601String()];
+    }
+
+    private function buildTickets(string $owner): Collection
+    {
         $sales = PosSale::owned($owner)
             ->openTickets()
             ->where('kitchen_status', PosSale::KITCHEN_ACTIVE)
@@ -36,7 +97,7 @@ class KitchenController extends Controller
             ->orderBy('kitchen_sent_at')
             ->get();
 
-        $tickets = $sales->map(function (PosSale $sale) {
+        return $sales->map(function (PosSale $sale) {
             $lines = $sale->lines
                 ->filter(fn (PosSaleLine $l) => in_array($l->kitchen_state, [
                     PosSaleLine::KITCHEN_QUEUED,
@@ -69,8 +130,6 @@ class KitchenController extends Controller
                 ])->all(),
             ];
         })->filter()->values();
-
-        return response()->json(['tickets' => $tickets, 'server_time' => now()->toIso8601String()]);
     }
 
     /**