Fix WLED LED stutters: restore DDP PUSH flag, skip HTTP during streaming

Three changes to eliminate periodic LED stutters on high-LED-count
WLED devices:

1. DDP PUSH flag: re-enable on the last packet of each frame so WLED
   waits for the complete frame before rendering (prevents tearing
   from partial multi-packet frames).

2. Health check: skip HTTP probe while a target is actively streaming
   to the device — the device is clearly online and the HTTP request
   to the ESP causes LED output to stutter.

3. Brightness polling: cache the value after first fetch and reuse it
   on subsequent 2-second UI refreshes instead of hitting the ESP
   every cycle.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/core/ddp_client.py

@@ -223,11 +223,10 @@ class DDPClient:
                 # Increment sequence number
                 self._sequence = (self._sequence + 1) % 256
 
-                # Build and send packet (no PUSH flag — WLED 0.15.x
-                # handles DDP without it; adding PUSH broke rendering)
+                # Set PUSH flag on the last packet to signal frame completion
                 packet = self._build_ddp_packet(
                     chunk, offset=start,
-                    sequence=self._sequence, push=False,
+                    sequence=self._sequence, push=is_last,
                 )
                 self._transport.sendto(packet)
 
@@ -273,10 +272,11 @@ class DDPClient:
             start = i * bytes_per_packet
             end = min(start + bytes_per_packet, total_bytes)
             chunk = pixel_bytes[start:end]
+            is_last = (i == num_packets - 1)
             self._sequence = (self._sequence + 1) % 256
             packet = self._build_ddp_packet(
                 chunk, offset=start,
-                sequence=self._sequence, push=False,
+                sequence=self._sequence, push=is_last,
             )
             self._transport.sendto(packet)
 

server/src/wled_controller/core/processor_manager.py

@@ -1002,6 +1002,13 @@ class ProcessorManager:
         state.health_task.cancel()
         state.health_task = None
 
+    def _device_is_processing(self, device_id: str) -> bool:
+        """Check if any target is actively streaming to this device."""
+        return any(
+            t.is_running for t in self._targets.values()
+            if t.device_id == device_id
+        )
+
     async def _health_check_loop(self, device_id: str):
         """Background loop that periodically checks a WLED device via GET /json/info."""
         state = self._devices.get(device_id)
@@ -1012,7 +1019,14 @@ class ProcessorManager:
 
         try:
             while self._health_monitoring_active:
+                # Skip health check while actively streaming — the device is
+                # clearly online and the HTTP request causes LED stutters
+                if not self._device_is_processing(device_id):
                     await self._check_device_health(device_id)
+                else:
+                    # Mark as online since we're successfully sending frames
+                    if state.health:
+                        state.health.online = True
                 await asyncio.sleep(check_interval)
         except asyncio.CancelledError:
             pass

server/src/wled_controller/static/app.js

@@ -4562,8 +4562,22 @@ async function loadTargetsTab() {
         devicesWithState.forEach(device => {
             attachDeviceListeners(device.id);
             if ((device.capabilities || []).includes('brightness_control')) {
+                // Only fetch from device if we don't have a cached value yet —
+                // avoids HTTP requests to the ESP every 2s which cause LED stutters
+                if (device.id in _deviceBrightnessCache) {
+                    const bri = _deviceBrightnessCache[device.id];
+                    const slider = document.querySelector(`[data-device-brightness="${device.id}"]`);
+                    if (slider) {
+                        slider.value = bri;
+                        slider.title = Math.round(bri / 255 * 100) + '%';
+                        slider.disabled = false;
+                    }
+                    const wrap = document.querySelector(`[data-brightness-wrap="${device.id}"]`);
+                    if (wrap) wrap.classList.remove('brightness-loading');
+                } else {
                     fetchDeviceBrightness(device.id);
                 }
+            }
         });
 
         // Manage KC WebSockets: connect for processing, disconnect for stopped