Vim built‑in package loading versus external plugin manager: interoperability for reproducible plugin sets

Goal: establish a repeatable Vim development environment where the exact plugin set and versions can be reproduced on any machine using only Vim’s startup mechanisms.

Uncertainty: Vim’s native package loading via runtimepath and pack/*/start loads plugins automatically but offers no dependency resolution or version pinning, requiring manual vendoring or submodules. External plugin managers (e.g., vim‑plug, dein.vim, minpac) provide declarative pinning through the vimrc but add their own runtimepath entries and may interact with defaults.vim and the presence or absence of a user vimrc. It is unclear how these two mechanisms coexist when both are present, and which strategy yields a more reliable, cross‑machine reproducible setup.

Specific questions:

• When both built‑in packages and an external plugin manager are present, how does Vim resolve duplicate plugin entries in runtimepath, and what effect does this have on startup time and plugin precedence?
• Does relying solely on Vim’s native pack/*/start layout with vendored copies, or delegating version control to an external plugin manager, provide a more dependable, reproducible environment given the interaction with defaults.vim and the optional user vimrc?