ettusresearch/gr-doa — reverse-engineered prompt

I want a working GNU Radio demonstration for finding where a radio signal is coming from using an Ettus USRP X440. It should show off the X440 receive channels staying phase synchronized, measure relative phase offsets, apply corrections, let me calibrate a linear antenna array, and estimate direction of arrival with MUSIC and Root MUSIC.

Please include runnable example apps and GNU Radio blocks so I can test phase sync first, then run a DoA demo with a known signal. I also need clear setup notes for Ubuntu 24.04 with UHD, GNU Radio, Armadillo, and the QA test tools, plus simple verification tests using Octave and Python where appropriate.

Keep it as a clean out of tree module that can be built with CMake and installed into GNU Radio Companion. If you need exact API details, look up the current UHD and GNU Radio docs online.