Ninja build fails on subcommand + Question about physical buttons

I am currently in the process of upcycling a broken Harman Karman Citation 100 speaker. The mainboard is fried but the speaker and power supply are working. I saw your project and decided to put an ESP32 in it with a DAC and extra amplifier board.

I am stuck building the firmware on my PC. I am running Debian 11, protobuf and grpcio-tools are installed in the .espressif python environment. Retried installing esp-idf from scratch, but that wasn't any help.

My logs show the following:

```
esptool.py v3.3-dev
Creating esp32 image...
Merged 1 ELF section
Successfully created esp32 image.
Generated /home/nova/Projects/esp/cspot/targets/esp32/build/bootloader/bootloader.bin
[97/97] cd /home/nova/Projects/esp/cspot/targets/esp32/build/bootloader/esp-idf/esptool_py && /home/nova/.espressif/python_env/idf4.4_py3.9_env/bin/python /home/nova/Projects/esp/esp-idf/components/partition_table/check_sizes.py --offset 0x8000 bootloader 0x1000 /home/nova/Projects/esp/cspot/targets/esp32/build/bootloader/bootloader.bin
Bootloader binary size 0x69b0 bytes. 0x650 bytes (6%) free.
[963/1445] Generating nanopb/generator/nanopb_generator.py, nanopb/generator/proto/nanopb.proto
FAILED: esp-idf/main/cspot/nanopb/generator/nanopb_generator.py esp-idf/main/cspot/nanopb/generator/proto/nanopb.proto
cd /home/nova/Projects/esp/cspot/targets/esp32/build/esp-idf/main/cspot && /usr/bin/cmake -E copy_directory /usr/bin /home/nova/Projects/esp/cspot/targets/esp32/build/esp-idf/main/cspot/nanopb/generator
Error copying directory from "/usr/bin" to "/home/nova/Projects/esp/cspot/targets/esp32/build/esp-idf/main/cspot/nanopb/generator".
[976/1445] Building C object esp-idf/bt/CMakeFiles/__idf_bt.dir/host/bluedroid/stack/l2cap/l2c_utils.c.obj
ninja: build stopped: subcommand failed.
ninja failed with exit code 1
```

I am out of ideas to get this to work, so any help would be greatly appreciated!

**Question about physical buttons**

I would really like to have the original control buttons of the Citation speaker working with cspot. I took apart the speaker and noticed an UART bus on the control panel, hooked this up to a USB-To-TTL converter, worked on the first try, a serial monitor shows which button is pressed and released.

Would there be a easy way to implement this in CSpot? I already took a look at some source files and my guess would be to modify the Player.h file, but maybe i am overseeing something. I am not a professional programmer, and my C skills aren't noteworthy. I know my way around PHP and Python, with some tinkering I am convinced I will get it to work.

Cheers!