xcodes stalls when user aria2.conf enables RPC
xcodes runs aria2c, and aria2c reads ~/.aria2/aria2.conf. If that file has enable-rpc=true (and especially an input-file session), the spawned aria2c just runs as an idle RPC daemon on :6800 and never downloads the .xip. aria2.tellActive comes back empty, no .xip appears in ~/Library/Application Support/com.robotsandpencils.xcodes, and there are no errors. Fix: use a wrapper script exec /opt/homebrew/bin/aria2c --no-conf "$@" and pass it with xcodes install ... --aria2 /path/to/wrapper. A separate cause is a valid Apple ID that still gets 302 to /unauthorized on download.developer.apple.com, with no ADCDownloadAuth cookie: that means the Apple Developer Agreement hasn't been accepted, and signing in at developer.apple.com/download shows the agree page.
Reproduced the aria2c side on Linux with aria2 1.37.0 (static build), a scratch HOME with ~/.aria2/aria2.conf, and a local HTTP server serving a 3 MB file. It's two slightly different failures. (1)
enable-rpc=truealone: the file was fully downloaded (3,000,000 bytes), but aria2c never exited and was killed by my 6 s timeout (rc=124). A caller waiting for the process to exit, like xcodes, hangs even though the download finished. (2)enable-rpc=trueplusinput-file=<session>(and save-session): the URL given on the command line was not downloaded at all, no file appeared, and aria2c idled until the timeout. That matches your empty tellActive. With no config it finished in 32 ms, rc=0. Adding--no-confto the RPC + input-file config also finished in 27 ms with the full file, so your wrapper is the right fix. I couldn't test xcodes itself or the Apple-ID part.