Desktop sidebar: no way to hide empty groups or sessions whose working directory is gone

## Summary

Two related pieces of sidebar clutter in the Claude Code desktop app (Code tab) that cannot currently be dismissed by any setting:

1. Custom sidebar groups with zero sessions stay visible forever, each rendering an empty header plus a "No active sessions" placeholder row.
2. Sessions whose working directory no longer exists stay in the sidebar, and opening one only produces Working directory no longer exists: <path>. The folder may have been moved, deleted, or unmounted.

Actual behavior

On my machine the sidebar had 90 custom groups, 45 of which contained 0 sessions (verified via the ccd_sidebar list_groups MCP tool and cross-checked per group with list_sessions --include_archived). Those 45 groups occupied roughly half the sidebar height with nothing in them. The only remedy was to delete each group one at a time.

Separately, a session pointing at a folder I had deleted two months earlier was still listed. Its history directory (~/.claude/projects/C--AI-Git) was last written 2026-07-28, and the folder itself no longer exists.

Expected behavior

A setting (or sensible default) that:

• Hides sidebar groups that currently contain zero sessions, and
• Hides or auto-archives sessions whose working directory no longer exists — ideally with a visible "stale" affordance rather than silent removal, so nothing is lost.

What already exists and why it does not cover this

| Existing feature | Why it does not help |
|---|---|
| Auto-archive after PR merge or close | Only triggers on PR state; most sessions here have no PR. |
| cleanupPeriodDays (default 90) | Age-based, not existence-based. A folder deleted yesterday still shows for 90 days. |
| Grouping toggle (state / directory) | Changes grouping, does not hide empty groups. |
| Manual group delete / manual archive | O(n) clicks; 45 groups meant 45 separate operations. |

Suggested shape

Two independent toggles under Settings → Claude Code, both defaulting to the current behavior so nobody is surprised:

• Hide empty sidebar groups
• Hide sessions whose working directory is missing (or Auto-archive sessions with a missing working directory)

Equivalent settings.json keys would let this be configured from the CLI as well.

Environment

• Claude Code desktop app, Code tab
• Windows 11 Pro 10.0.26200
• ~45 active custom sidebar groups after cleanup, ~90 before