fix: clamp padding size to prevent UDP fragmentation on LTE/cellular and dynamically report connection status

ostp-client/src/bridge.rs

@@ -661,8 +661,19 @@ impl Bridge {
         let throughput = incoming.saturating_add(outgoing);
 
         tx.send(UiEvent::Traffic { incoming_bps: incoming, outgoing_bps: outgoing }).await.ok();
+
+        // Dynamically report connection status based on whether we have received server packets recently (last 10 seconds)
+        let is_healthy = self.last_valid_recv.elapsed() < Duration::from_secs(10);
+        let status = if is_healthy {
+            self.metrics.connection_state.store(2, Ordering::Relaxed);
+            ConnectionStatus::Established
+        } else {
+            self.metrics.connection_state.store(1, Ordering::Relaxed);
+            ConnectionStatus::Handshaking
+        };
+
         tx.send(UiEvent::Metrics {
-            status: ConnectionStatus::Established,
+            status,
             rtt_ms: self.last_rtt_ms,
             throughput_bps: throughput,
         }).await.ok();

ostp-core/src/framing/padding.rs

@@ -45,7 +45,7 @@ impl AdaptivePadder {
     }
 
     pub fn padding_for_len(&self, payload_len: usize) -> usize {
-        match self.strategy {
+        let raw_pad = match self.strategy {
             PaddingStrategy::Fixed(target) => target.saturating_sub(payload_len),
             PaddingStrategy::Adaptive => {
                 let base_bucket = 64;
@@ -69,7 +69,12 @@ impl AdaptivePadder {
                 let target = prof.target_size(payload_len);
                 target.saturating_sub(payload_len).min(self.max_pad)
             }
-        }
+        };
+
+        // Strict clamp to ensure total packet size (including overhead) never exceeds mtu_hint
+        let overhead = 38;
+        let max_allowed = self.mtu_hint.saturating_sub(payload_len).saturating_sub(overhead);
+        raw_pad.min(max_allowed)
     }
 
     pub fn build_padding(&self, payload_len: usize) -> Vec<u8> {