[idea] group spaces into user-created folders in the sidebar

[leondewey]

idea / problem

Once I have more than a handful of spaces the flat list is hard to navigate; the only grouping today is automatic git-worktree grouping. I'd also like to reclaim the height the agents section uses when I'm not using it.

requested change

User-created folders for spaces: create/rename/delete, assign via right-click / a picker / drag-and-drop, collapsible, reusing the existing worktree-group rendering; membership persisted in the session snapshot (version bump + migration). Also moves the agents-section toggle into the sidebar "menu". Folder definitions/membership are exposed via neutrally-named JSON API + events (workspace_group.*, workspace.assign_group, group_id on WorkspaceInfo) per the runtime/client boundary in AGENTS.md; collapse stays presentation-only. This bumps the wire protocol, so I'd want your input on the API shape first.

https://github.com/leondewey/herdr/tree/sidebar-grouping working prototype on a branch; happy to split into smaller PRs.

why you want this

Keep a larger set of spaces organized, and hide the agents panel when not needed.

[delltrak]

This would solve an important multi-client workflow for me.

I use one workspace per project and need tabs to remain available for project-specific views such as agents, servers, logs, and reviews.

Generic workspace folders would let me organize the sidebar as:

• Client A
  • website
  • API
• Client B
  • platform

Using one named session per client loses the unified agent overview, while using tabs as projects removes the project-level tab organization.

I would be interested in testing the existing prototype on macOS and helping with implementation if the direction is accepted.