cli: rework +ssh-cache internals and user interface

[jparise]

This change primarily focused on a revised +ssh-cache user interface, but it also reworks a bunch of the internals.

The primary CLI improvement is support for positional arguments and a consistent list output format that includes both the ISO-formatted timestamp and relative age.

ghostty +ssh-cache                           # List all cached destinations
ghostty +ssh-cache user@example.com          # Show that destination
ghostty +ssh-cache example.com               # Show all users on that host
ghostty +ssh-cache --add=user@example.com    # Manually add a destination
ghostty +ssh-cache --remove=user@example.com # Remove a destination
ghostty +ssh-cache --prune=30d               # Remove entries older than 30 days
ghostty +ssh-cache --clear                   # Clear entire cache

Notable, we now support a --prune operation that replaces the previous --expire-days flag that was never actually hooked up to anything (!!). --prune also supports a wider range of Duration-based values.

We're also much more consistent with error codes: 0=success, 1=failure, 2=usage.

While working on those changes, I also reworked the cache internals, particularly the code around timestamp handling and errors. For example, I dropped the explicit error sets because they were growing unwieldy, and in practice we only matched on a subset of those errors.

Lastly, overall test coverage should be much improved, especially around the time- and allocation-related operations.

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AI Disclosure: I made a lot of iterative, AI-assisted (Claude Opus 4.7) correctness passes over this work. It was particularly helpful in tracing through the various failure modes, and it wrote those unit tests in the process.

[tristan957]

Do we have have any precedent for subcommands? I generally prefer ghostty +ssh add xyz whereas you have gone with long options. Obviously being consistent is better than anything, but figured I would bring it up.

[jparise]

Do we have have any precedent for subcommands? I generally prefer ghostty +ssh add xyz whereas you have gone with long options. Obviously being consistent is better than anything, but figured I would bring it up.

This maintains the +ssh-cache interface that's already shipped, which used options rather than subcommands. I think it would be fine to further revise this to use commands (with compatibility for the previous flags), but that might be for a follow-up change given all of the things this already does.

I don't think I'd try to merge this functionality into +ssh, because that's positioned as a ssh wrapper, and it's command line parsing already has a high bar to avoid ambiguities between the Ghostty-specific flags and SSH's.

[tristan957]

Do we have have any precedent for subcommands? I generally prefer ghostty +ssh add xyz whereas you have gone with long options. Obviously being consistent is better than anything, but figured I would bring it up.

This maintains the +ssh-cache interface that's already shipped, which used options rather than subcommands. I think it would be fine to further revise this to use commands (with compatibility for the previous flags), but that might be for a follow-up change given all of the things this already does.

I don't think I'd try to merge this functionality into +ssh, because that's positioned as a ssh wrapper, and it's command line parsing already has a high bar to avoid ambiguities between the Ghostty-specific flags and SSH's.

Makes sense. Thanks!