feat: configurable compaction

[maxeonyx]

This will help to address the manyissuesaboutcompaction

Closes#3031

I have had great success using this version with a custom "handover" compact prompt.

example: override /compact with compact.md

This will now affect auto-compaction.

~/.config/opencode/command/compact.md

---description: my custom compactcompact: true---
Provide a detailed summary focusing on ...

example: custom command /handover

~/.config/opencode/command/handover.md

---description: handover to new agentcompact: true---
Produce a handoff note from this conversation ...

example: set auto-compact to use /handover

~/.config/opencode/opencode.json

{
"compaction": {
"command": "handover"
}
}

---

I have spent a lot of time making this PR as small and well integrated as possible, as I'm relying on it for my day-to-day work.

[rekram1-node]

@maxeonyx have u seen how we handle /init?

I was thinking a cleaner solution here would be to make compact a built in slash command, a user could override the prompt by defining their own compact and it wouldn't require additional config fields

The main change this would require is allowing slash commands to register functions to execute, which ofc couldn't be done in json but perhaps for now that functionality would remain internal

[maxeonyx]

I haven't seen that, no, but I assumed compact has special handling due to the fact that it replaces the full context window. I am very open to doing this a different way.

[maxeonyx]

@rekram1-node in your suggestion, then, I would define my own /handover slash command, with a different prompt, and configured to remove the rest of the context same as /compact (and we would also make /compact be implemented the same way)

[einarpersson]

@rekram1-node

@maxeonyx have u seen how we handle /init?

I was thinking a cleaner solution here would be to make compact a built in slash command, a user could override the prompt by defining their own compact and it wouldn't require additional config fields

The main change this would require is allowing slash commands to register functions to execute, which ofc couldn't be done in json but perhaps for now that functionality would remain internal

I agree, I think
1.compact should be a default includes slash command
2. Default included slash commands should be able to be overriden by user custom commands
3. User custom commands should be able to run as functions, something like #4411

I would advocate for trying to build the built-in slash commands such as /compact with the sdk, in other words forcing yourself to use the same functionality that a custom plugin developer would use. That would drive a architecture which makes sure that user custom commands can be just as powerful as the ones provided by default.

[rekram1-node]

Yup total agreement, currently jumping between several fixes and then I can come back to these new feature prs

[maxeonyx]

I have the new version mostly implemented but I'm on holiday atm - feel free to take it over or close as I won't able to do the final "runnable as functions" part. But I have done the "custom md file to implement custom compact-type command". I can add precedence for overriding /compact - that's a good idea.

[maxeonyx]

@rekram1-node@einarpersson This PR is ready for your review, hope it's what you are imagining. It has turned out pretty clean I think.

[maxeonyx]

@rekram1-node Keeping this up-to date is becoming a hassle - would you be able to review?

[github-actions]

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