Problem:
vim.lsp.util.show_document() can fail to load the target buffer, most
visibly with E325 when another process owns the file's swapfile and the
user declines to open it. The Vim error escapes show_document() and
surfaces inside whichever LSP handler called it, instead of being
reported as a failure to show the document.
Solution:
Load the buffer up front with vim.fn.bufload(), before any of that
state is touched, and report the error instead of raising.
AI-assisted
ce5e230af8