Fix BLE upload: write-with-response on CMD+DATA, on-demand advertising, wake-play-random, remove startup blink

app/ble.js

@@ -186,7 +186,7 @@ export class BabyMobile extends EventTarget {
 
   async _writeCmd(bytes) {
     this._requireConnected();
-    await this.cmd.writeValueWithoutResponse(Uint8Array.from(bytes));
+    await this.cmd.writeValue(Uint8Array.from(bytes));
   }
 
   async play(track) {
@@ -282,21 +282,21 @@ export class BabyMobile extends EventTarget {
       this._log(`Starting upload of ${total} bytes to slot ${track}…`);
       await this._writeCmd([CMD_UPLOAD_START, track & 0xff]);
 
-      // Send all data chunks sequentially.  Chrome on Windows (WinRT BLE) only
-      // allows one writeValueWithoutResponse in flight at a time; concurrent calls
-      // fail with "GATT operation already in progress".  Sequential writes are
-      // reliable and throughput is governed by the BLE connection interval, not
-      // by how many calls are in flight.
+      // Send all data chunks using write-with-response.  Each writeValue() call
+      // blocks until the SoftDevice sends an ATT Write Response, which only happens
+      // after it has delivered the packet to the firmware's write callback.  This
+      // provides natural per-packet flow control: CMD_UPLOAD_END cannot be sent until
+      // every data packet has been confirmed received, eliminating all OS TX-queue
+      // race conditions without any byte-counting hacks.
       for (let off = 0; off < total; off += DATA_CHUNK) {
-        await this.data.writeValueWithoutResponse(
+        await this.data.writeValue(
           wavBytes.subarray(off, Math.min(off + DATA_CHUNK, total)));
         // Cap the optimistic local count at 99%; the final 1% is filled only when
         // the device's finalize ack confirms the bytes actually landed in flash.
         report(Math.min(off + DATA_CHUNK, Math.floor(total * 0.99)));
       }
 
-      // Tell the firmware we're done. It will drain its ring buffer, write the
-      // track table, then send ONE finalize notification with the total byte count.
+      // All data confirmed received — finalize.
       await this._writeCmd([CMD_UPLOAD_END]);
 
       // Wait for that single finalize notification.  Allow up to 60 s: at 300 ms/sector