jfjoch_broker: Export writer FIFO utilization for TCP socket

image_pusher/TCPStreamPusher.cpp

@@ -592,6 +592,8 @@ void TCPStreamPusher::PersistentAckThread(Connection* c) {
             break;
         }
 
+        c->last_ack_fifo_occupancy.store(h.ack_fifo_occupancy, std::memory_order_relaxed);
+
         // ACK frame — forward to data-collection ack logic
         std::string error_text;
         if (h.payload_size > 0) {
@@ -1143,3 +1145,13 @@ std::optional<uint64_t> TCPStreamPusher::GetImagesWritten() const {
 std::optional<uint64_t> TCPStreamPusher::GetImagesWriteError() const {
     return total_data_acked_bad.load(std::memory_order_relaxed);
 }
+
+std::vector<int64_t> TCPStreamPusher::GetWriterFifoUtilization() const {
+    std::vector<int64_t> ret;
+    std::lock_guard lg(connections_mutex);
+    ret.reserve(connections.size());
+    for (const auto& c : connections) {
+        ret.push_back(c->last_ack_fifo_occupancy.load(std::memory_order_relaxed));
+    }
+    return ret;
+}