#20905 cmux NEXT sidebar: group by status, ported onto the Priority state (Debug toggle, off)

The sidebar's computer sections can be grouped by agent status, behind the Debug toggle Group by status (sidebar.groupByStatus), which is off by default. Turn it on in Debug Settings > Sidebar (palette: Open Debug Settings). With the toggle off, the sidebar lays out exactly as before.

Leo, 2026-10-21: "#20905: adopt it rather than building a second auto-sections. Keep it behind the Debug toggle, off by default, then bring it current, get a review and land it."

This PR is now ported onto current feat-cmux-next. Since #20905 was first written, base gained the Priority state (AgentPriorityRanking), the session tree, S1/S3 row status, the Done fold (#23633) and Show more (#23671). The port builds on those instead of carrying its own copies.

What changes

• Sections. Each computer's workspaces sit under one header per Priority state. The sections are, in Priority's tier order: Needs you, Done, Failed, CI failing, Working, Idle.
  • The state is the row's agentChip (AgentPriorityRanking.state and .tier). A row with no chip falls back to Working or Idle.
  • Headers reuse the Priority view's strings, so the string catalog is unchanged.
  • Each header shows a count.
• Stable order. Inside a section, rows keep their manual order.
  • The active row keeps its section until another row becomes active, so nothing jumps under you.
  • A plain click doesn't relayout ("a click moves no row", #22960), so a released row moves at the next relayout.
• Folding. Each header folds and keeps its count, except Needs you, which never folds.
  • Turning the toggle off forgets the held row and the folds.
• Locked while grouped. Drag reorder is locked while the list is grouped, as it already is under Group by Folder.
• No Done fold or Show more inside status sections. A Done workspace shows under its own state. A status section lists every row even when sidebar.groupRowLimit is set.
• Dropped from the original #20905:
  • its own status classifier (SidebarStatusBucket): the Priority state replaces it;
  • the row status marks: S1/S3 already draw row status;
  • the agent-parent elbow and its toggle (sidebar.statusElbow): the session tree replaces it;
  • the Package.swift and ci-target-graph.json edits.
• Supporting changes.
  • Group by Folder's bucketing moved to SidebarLayout+Folder.swift.
  • Both god files shrink: SidebarLayout.swift goes from 461 to 459 lines, and SidebarModel.swift stays at 565.

No capture: the change is behind a Debug toggle that is off by default, and with it off nothing draws differently. Stills will go on #16541 once someone dogfoods it.

Evidence

• SidebarStatusGroupingTests (8 cases) drives a real SidebarView and reads the drawn rows and header labels. It covers:
  • tier and manual order;
  • toggle off giving the old list, with reorder unlocked;
  • a row moving when its state changes, while the active row waits;
  • folding, and Needs you never folding;
  • toggle off clearing the folds and the held row;
  • Done staying under its state;
  • no Show more row at a row limit of 10 with 14 rows;
  • the classifier end to end.
• Red: the test commit 05389f2 alone doesn't compile, because it calls the new toggle and types. Green: the port.
• The fleet compile-check --app passed at 31d66cd and again at 55cf9cc, which only disambiguates SidebarSection in the test. The focused suite run had not reported when this merged; a red there would be fixed forward.
• prepush-gate.py reports no new violations.

Observed / Not run

Observed: the fleet compile at the head, the pre-push gate, and an independent review (receipt in the comments). Not run: a confirmed focused suite result, a capture, and a live dogfood of the toggle in a DEV build.

Takes back #23671: not a take-back. The .showMore cases that S5 added to row-key switches gain a .status case beside them, and Show more's behavior is unchanged.
Takes back #23633: not a take-back. The .doneFold cases that S4 added to row-key switches gain a .status case beside them, and the Done fold's behavior outside status sections is unchanged.

Changelog

none (behind a Debug toggle, off by default)

Agent session: cosmic-gray

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