[ci] Give the custom BYOD build a name for the agent

[elliot-barn]

What

Passes --add-host rayci.localhost:host-gateway to the docker build that builds custom BYOD images, which is what wanda already passes to every image build it starts (ray-project/rayci#501).

Why

Release build 104848, on the commit that became #65578, failed hello_world_custom_byod.aws and hello_world_custom_byod.gce:

#11 6.043 error: Request failed after 3 retries in 5.7s
#11 6.043   Caused by: failed to lookup address information: No address associated with hostname
#11 ERROR: process "/bin/bash -c bash /tmp/install_python_deps.sh python_depset.lock" did not complete successfully: exit code: 2

Custom BYOD images are built here by a plain docker build, not by wanda, so they inherit none of wanda's networking flags. RAYCI_IMAGE_PIP_INDEX_URL reaches the build as http://rayci.localhost:35999/simple — a name the build has no way to resolve — and install_python_deps.sh resolves the depsets with uv, which fails hard where pip would have fallen back to PyPI. So the image build dies rather than degrading.

Everything else on that build was green (78 passed at the time, including wanda: forge, all five wheel builds, the base-extra-testdeps images, and the hello_world* release tests on AWS, GCE and released images) — this is the one path that reaches the agent proxy without going through wanda.

Unconditional, matching wanda: docker resolves host-gateway itself, and one extra hosts entry is inert for a build that never uses the name.

Testing

python -m pytest release/ray_release/tests/test_byod_build.py — 4 passed. The flag goes in after -t <image>, so the argument prefix those tests match on is unchanged.

AI assistance was used for this change.

[gemini-code-assist]

Code Review

This pull request updates the custom BYOD image build command in release/ray_release/byod/build.py to include the --add-host rayci.localhost:host-gateway flag. This change ensures that the plain docker build can resolve rayci.localhost to the host gateway, preventing dependency resolution failures during the build process. There are no review comments, so I have no feedback to provide.