fix(network): prevent near-zero bandwidth on rapid event-driven updates

When netlink events (link/addr/route changes) fire between timer
intervals, dp.emit() triggers update() which consumes the byte delta
and resets bandwidth_down_total_. A subsequent timer update sees
near-zero delta, displaying very small bandwidth.

Cache the last computed bandwidth values and skip recalculation
when update() is called within half the interval. Event-driven
updates reuse the cached values instead.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

include/modules/network.hpp

@@ -70,6 +70,8 @@ class Network : public ALabel {
 
   unsigned long long bandwidth_down_total_{0};
   unsigned long long bandwidth_up_total_{0};
+  unsigned long long bandwidth_down_prev_{0};
+  unsigned long long bandwidth_up_prev_{0};
   std::chrono::steady_clock::time_point bandwidth_last_sample_time_;
 
   std::string state_;

src/modules/network.cpp

@@ -280,14 +280,22 @@ auto waybar::modules::Network::update() -> void {
   std::string tooltip_format;
   auto now = std::chrono::steady_clock::now();
   auto elapsed_seconds = std::chrono::duration<double>(now - bandwidth_last_sample_time_).count();
+
+  auto bandwidth_down = 0ull;
+  auto bandwidth_up = 0ull;
+
+  // Only recalculate bandwidth when enough time has elapsed since the last
+  // sample.  Event-driven dp.emit() calls (link/addr/route changes) can
+  // trigger update() between timer intervals, which would consume the byte
+  // delta prematurely and show near-zero bandwidth.
+  auto min_elapsed = std::chrono::duration<double>(interval_).count() * 0.5;
+  if (elapsed_seconds >= min_elapsed) {
     if (elapsed_seconds <= 0.0) {
       elapsed_seconds = std::chrono::duration<double>(interval_).count();
     }
     bandwidth_last_sample_time_ = now;
 
     auto bandwidth = readBandwidthUsage();
-  auto bandwidth_down = 0ull;
-  auto bandwidth_up = 0ull;
     if (bandwidth.has_value()) {
       auto down_octets = (*bandwidth).first;
       auto up_octets = (*bandwidth).second;
@@ -297,6 +305,14 @@ auto waybar::modules::Network::update() -> void {
 
       bandwidth_up = up_octets - bandwidth_up_total_;
       bandwidth_up_total_ = up_octets;
+
+      bandwidth_down_prev_ = bandwidth_down;
+      bandwidth_up_prev_ = bandwidth_up;
+    }
+  } else {
+    bandwidth_down = bandwidth_down_prev_;
+    bandwidth_up = bandwidth_up_prev_;
+    elapsed_seconds = std::chrono::duration<double>(interval_).count();
   }
 
   if (!alt_) {