put_to_history wrote entries without a trailing newline, so fixed
commands concatenated onto one line, and backslash-continued
multiline entries were read back as broken fragments. Join
continuations when reading and terminate entries with a newline,
matching the fish adapter convention.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
Alexander