[CI] Support partial torch requirement contexts

[taneem-ibrahim]

Purpose

A clean CUDA CI image build runs use_existing_torch.py from a partial test-deps context without pyproject.toml, causing dependency setup to fail before tests. Treating that file as optional preserves the dependency cache while supporting partial contexts.

Reproducer

Run python use_existing_torch.py --prefix with requirements/ present and no pyproject.toml.

Output on main / on branch

Main: FileNotFoundError: [Errno 2] No such file or directory: 'pyproject.toml'

Branch: 8 passed, 14 warnings in 1.40s

Test Plan

.venv/bin/python -m pytest tests/tools/test_docker_build_metadata_args.py -q

AI assistance disclosure

OpenAI Codex (GPT-5) drafted the code and PR text. All changed lines were human-reviewed and tests human-run.

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[yewentao256]

Thanks foe the work!

[yewentao256]

LGTM, thanks for the work!

[yewentao256]

Suggested change

	import sys
	from pathlib import Path
	REPO_ROOT = Path(__file__).resolve().parents[2]
	HELPER = REPO_ROOT / ".buildkite" / "scripts" / "docker-build-metadata-args.sh"
	USE_EXISTING_TORCH = REPO_ROOT / "use_existing_torch.py"
	from pathlib import Path
	REPO_ROOT = Path(__file__).resolve().parents[2]
	HELPER = REPO_ROOT / ".buildkite" / "scripts" / "docker-build-metadata-args.sh"

Now becomes unused import

[github-actions]

✅ @taneem-ibrahim, CI is now available for this PR.

• /ci run starts a CI build.
• /ci retry retries failed jobs in the CI build for the current PR head. If the current head has no CI build, it starts a new CI build for the current head containing only jobs that failed in the latest earlier CI build for this PR.
• /ci cancel cancels scheduled or running CI builds for this PR branch.

[mergify]

Hi @taneem-ibrahim, the pre-commit checks have failed. Please run:

uv pip install pre-commit>=4.5.1
pre-commit install
pre-commit run --all-files

Then, commit the changes and push to your branch.

For future commits, pre-commit will run automatically on changed files before each commit.

[taneem-ibrahim]

/ci run

[github-actions]

✅ Triggered Buildkite CI #83374 for commit 55420eb25027.

[taneem-ibrahim]

/ci run

[github-actions]

✅ Triggered Buildkite CI #83381 for commit ff3a08a0ab5f.