mcore-split-pr

# Split PR by CODEOWNERS Groups Split a large pull request into multiple smaller PRs, where each PR touches the fewest possible CODEOWNERS reviewer groups. The goal is to reduce review burden: a PR that only touches `megatron/core/` needs only the core reviewers, while a PR that also touches `examples/`, `tools/`, and `megatron/training/` pulls in many additional groups. ## Answer-First Constraints For split-planning questions, lead with these constraints before the full workflow: - Minimize CODEOWNERS reviewer groups per PR, but each resulting PR must still be independently mergeable and reviewable. - Tests travel with the production code they validate; do not split tests into a separate PR just to reduce reviewer groups. - If PR B depends on symbols renamed in PR A, call out the dependency and put backward-compatible aliases, re-exports, or shims in PR A when needed. - Wait for user approval before execution. - Execution creates draft PRs from the right base, applies file-scoped diffs with `git diff upstream/main..<source-branch> -- <paths> | git apply`, pushes to the user's fork, and never pushes directly to upstream. ## Workflow ### 1. Analyze the PR 1. Fetch the PR details: `gh pr view <number> --repo NVIDIA/Megatron-LM --json title,body,headRefName,author` and `gh pr diff <number> --repo NVIDIA/Megatron-LM --stat`. Also determine the current GitHub user with `gh api user --jq .login`. 2. Parse `.github/CODEOWNERS` to build a mapping from file path patte...