Verified:
- ~/.local/share/nvim/mason/bin/gopls version v0.23.0, go vet OK for all 7 modules
- nvim --headless edit formatIO/main.go → 0 diagnostics (was EOF on empty)
- nvim --headless edit /tmp/should_show_eof.go (empty) → 1 diag expected 'package', found 'EOF' — expected, template will prevent.
