0112 — Sidebar navigation stays put while status changes

Status: Accepted Date: 2026-09-11

Context

ADR-0089 deliberately let an empty attention queue disappear and sorted rows by urgency and last change. In daily use this moves both navigation targets and section headers while the user is working. The sidebar becomes difficult to learn spatially and a changing agent can displace the session the user was about to click. Host-qualified session inventory now exists (ADR-0107), but the strip hides that context.

Decision

1. Two fixed panels. After reserving the footer, half the sidebar body belongs to Agents and the remainder to Sessions. Population never changes this split. Both areas keep headers and quiet empty states. Only an explicit viewport resize changes their allocation. Tiny viewports degrade within their bounds, prioritizing Sessions when only one body row is available.
2. Stable agent order. Sessions use stable session-id order; agents retain their session’s window/leaf order. State, attention, timestamps and review flags never participate in sorting. Agent creation, removal and explicit layout changes may change membership; lifecycle transitions do not.
3. Sessions include the current session. Session name and host are separate rows, with current-session windows nested below. The tab strip remains the complete window-navigation surface. Each panel has bounded overflow: Agents opens the fleet dashboard, Sessions opens the session picker.
4. Host identity comes from the server. Local-to-server sessions use the existing whoami record’s hostname, with this server as an honest fallback. Satellite sessions use their host inventory’s routing alias, and their clicks carry both host and session name. A local session containing a satellite pane remains a session on the serving server. An unreachable host remains visible as an inert placeholder.
5. Project once, paint incrementally. Peer metadata and inventory replies dirty the sidebar model. The burst drain rebuilds it once and schedules changed chrome without clearing pane contents. Peer layout broadcasts use the same agent-watch reconciliation as GET replies. Workspace membership, not mirror-slot allocation, identifies local agent broadcasts. Early question flags survive until the persisted layout resolves ownership; the server need not repeat a coalesced question.

Consequences

• Calm periods leave useful breathing room instead of moving Sessions upward. The user can learn where each area and ongoing agent lives.
• Urgency remains visible through glyphs and color, without overriding spatial navigation. The explicit fleet dashboard may keep its task-oriented ranking.
• A full panel can hide a newly blocked agent below overflow. That trade-off is deliberate: attention shortcuts and the fleet remain available; the sidebar is a stable navigation surface.
• Review lifetime remains a separate client-state defect (phux-deya). A session switch can still reset review badges, but it cannot reorder sidebar rows.
• No wire or server state is added. Host inventory is a snapshot refreshed by existing lifecycle/picker sweeps, not a claim of a new live federation feed.

Validation

• Empty, working, blocked and completed fleets leave both headers on the same rows at a fixed viewport; identical projections emit no bytes.
• Focus/review and lifecycle transitions preserve agent target order.
• Session labels identify the serving hostname and satellite alias; identical names on different hosts retain distinct click actions.
• GET and broadcast peer changes reach a quiet visible sidebar with the fleet closed; a broadcast introducing a leaf requests its metadata and watch.
• Short/narrow viewports remain bounded, overflow stays reachable, and real terminal captures verify top tabs and split sidebar together.