Read notes verbatim and insert the final newline only when it is missing,
instead of stripping the terminator on load and appending it unconditionally
on save. The editor's `rows = #\n + 1` model then renders a file's POSIX
terminator as a visible trailing blank line — what a writer expects: open a
note and see (and land the caret on) the empty line the newline stands for.
Supersedes the strip-on-load / unconditional-append handling that shipped
with the prefs work (c535864), which kept the buffer newline-free and hid the
terminator. Load + save are now an identity round-trip for any device-written
file (all end in '\n'); files stay git-clean (exactly one terminator); and a
trailing blank line the writer leaves is mirrored, never doubled.
- load_path: read verbatim (drop the strip)
- save_path: guarded final-newline (drop the unconditional append)
- Prefs::to_toml: ends in a newline again — the guarded save leaves exactly
one, so the prefs file is byte-identical to before and its device-verified
round-trip still holds
- sd_fat spike: payload ends in '\n' so its exact-equality round-trip holds