fix(ui): enforce save semantics for default and preset chunks

src/controllers/preset.py

@@ -171,9 +171,13 @@ async def send_presets(request, session):
     if not sender:
         return json.dumps({"error": "Transport not configured"}), 503, {'Content-Type': 'application/json'}
 
-    async def send_chunk(chunk_presets):
-        # Include save flag so the led-driver can persist when desired.
-        msg = build_message(presets=chunk_presets, save=save_flag, default=default_id)
+    async def send_chunk(chunk_presets, is_last):
+        # Save/default should only be sent with the final presets chunk.
+        msg = build_message(
+            presets=chunk_presets,
+            save=save_flag and is_last,
+            default=default_id if is_last else None,
+        )
         await sender.send(msg, addr=destination_mac)
 
     MAX_BYTES = 240
@@ -195,7 +199,7 @@ async def send_presets(request, session):
             last_msg = test_msg
         else:
             try:
-                await send_chunk(batch)
+                await send_chunk(batch, False)
             except Exception:
                 return json.dumps({"error": "Send failed"}), 503, {'Content-Type': 'application/json'}
             await asyncio.sleep(send_delay_s)
@@ -205,7 +209,7 @@ async def send_presets(request, session):
 
     if batch:
         try:
-            await send_chunk(batch)
+            await send_chunk(batch, True)
         except Exception:
             return json.dumps({"error": "Send failed"}), 503, {'Content-Type': 'application/json'}
         await asyncio.sleep(send_delay_s)