描述
Decide when Git submodules are the right external-repo boundary, then choose one safe operator flow: add and pin, bootstrap recursively, sync to the recorded commit, advance a tracked branch, edit inside the submodule without detached-HEAD surprises, remove cleanly, or configure CI/hosted-platform checkout constraints. Use when the user asks about `.gitmodules`, `git submodule`, recursive clone/setup, pointer updates, detached HEAD, private submodules in CI, GitHub Pages submodule limits, or submodule vs subtree/vendoring/package delivery. Not for generic Git history cleanup or package-manager dependency delivery.