[idea] Let plugins add a mode to the agent panel sort control

[karbassi]

idea / problem

The agent panel sorts two ways, grouped and priority, and the control cycles between them. Both are good. I keep mine on priority.

What I can't do is add a third. Priority tells me what needs me right now, which is most of what I need. It doesn't tell me what's gone quiet, and with around 20 agents open, that's the thing I keep missing.

requested change

I'd like a plugin to be able to add a sort mode to that control. The two built in modes stay unchanged and stay the default, and if no plugin adds one, the control works exactly like it does today.

A plugin can already attach its own values to a pane, and the panel can already order by them. What's missing is a way to offer that ordering as a mode you can pick and keep.

why you want this

I run around 20 Claude Code agents in one session, one workspace per git worktree. Priority order is right for triage and I don't want to give it up.

Sorting by session age would have caught something I sat on for weeks. I had 3 agents open for 18 days and no idea they were sitting there. Nothing in the panel surfaces that, because no built in mode orders by age and there's no way to add one.

Age is my case. Other plugins already track token spend, cost, branch, and PR state, and none of them can offer an ordering either.

[SteveHolloway71]

Second use case for this, from a different angle to age.

I want to keep spaces grouping but order the groups by attention — the space holding a blocked agent floats to the top, agents stay with their space. I've filed that as a specific built-in mode in #3400, but I'd genuinely rather have your version than mine: if a plugin could register a mode, I'd build it myself and withdraw the ask.

The reason your framing is the better one is what happens when you try to do this from outside today. workspace.move_block and workspace.report_metadata are both in the socket API, so a plugin can reorder spaces and annotate their rows — but reordering the real spaces to change how they display mutates state every other consumer shares, and unlike reported metadata a move has no ttl_ms, so a publisher that dies leaves the spaces shuffled with nothing to expire the claim.

So the workaround for a missing sort mode is to move the data. That's the wrong shape, and it's an argument for exactly the extension point you're describing: a plugin can already supply the value and the panel can already display it — it just can't offer it as an ordering.

Scale here is 28 agent panes across 11 spaces on one machine, so the same "around 20 agents and the panel stops answering the question" problem you describe.