As others have noted, npm install can/will change your lockfile as it installs, and one caveat for the clean-install command they provide is that it is SLOW, since it deletes the entire node_modules directory. Lots of people have complained but they have done nothing: https://github.com/npm/cli/issues/564
The npm team eventually seemed to settle on requiring someone to bring an RFC for this improvment, and the RFC someone did create I think has sat neglected in a corner ever since.
Is there no flag to opt out of this behavior? For Rust, Cargo commands will also do this by default, but they also have `--offline` for not checking online for new versions, `--locked` to require sticking with the exact version of the lockfile even when allowing downloading dependencies online (e.g. if you're building on a machine that's never downloaded dependencies before, so they aren't cached locally, but you still don't want to allow implicit updates), and `--frozen` (which is a shorthand for both `--locked` and `--offline`). I'm honestly on the fence about whether this is even sufficient, since I've worked at multiple places where the CI didn't actually run with `--locked` because whoever configured it didn't realize, and at least once a surprise update to the lockfile in CI ended up causing an issue that took a bit of time to debug before someone realized what was going on.
The npm team eventually seemed to settle on requiring someone to bring an RFC for this improvment, and the RFC someone did create I think has sat neglected in a corner ever since.