[Feature] Restore in-sidebar channel list (or make it optional vs the popover)

[brendandebeasi]

Summary

The chat/conversation switcher in the agent portal is now a popover (PortalHistoryPopover) rather than a persistent list. For users with many channels per agent, this loses at-a-glance visibility into unread state, recently-active channels, and which conversation is currently selected. A persistent list (or at least an option to enable one) would close that gap.

Current state

• interface/src/routes/AgentChat.tsx is a 5-line shim that renders <PortalPanel agentId={…} />
• Channel/conversation switching lives in interface/src/components/portal/PortalHeader.tsx:116-130 as a PopoverRoot wrapping PortalHistoryPopover — click-to-open dropdown
• The sidebar (interface/src/components/Sidebar.tsx:67-74) only exposes top-level agent sub-nav: Chat | Channels | Memory | Skills | Schedule | Config — no per-channel entries
• This was introduced in commit c53a1e38 (2026-04-04, "SpaceUI migration: sidebar redesign…") which redesigned the sidebar to a fixed-shape accordion. Prior to that, channels were visible directly in the sidebar.

Proposed change

User-configurable switcher style:

• New setting (Settings → Appearance, or per-agent): Channel switcher: sidebar | popover (default: keep current popover to avoid surprise; or flip if maintainers prefer)
• When sidebar, render channel list under the agent in Sidebar.tsx with last-message preview + unread badge, similar to the pre-c53a1e38 layout
• When popover, keep today's PortalHistoryPopover exactly as-is
• Persist setting in localStorage (or per-user once [Feature] Multi-user accounts + role-based access control for the API/dashboard #584 lands)

Related

• [Feature] Migrate sidebar from Agents to Humans #458 — proposes a different sidebar concept ("Migrate sidebar from Agents to Humans"). Worth coordinating: a configurable switcher style fits inside either layout.
• [Feature] Agent chats doesn't have threads like cortex chat #439 — thread support in agent chat. Threads inside a channel would benefit even more from a sidebar-style hierarchical view.

Open questions

• Was the popover an intentional simplification, or a side-effect of the SpaceUI migration? If the latter, should the default be sidebar for power users with >5 channels per agent?