Windows desktop app: session stuck showing 'working' spinner after background agents complete

Environment

• Claude Code 2.1.6, desktop app on Windows 11 Enterprise (10.0.26100)
• Model: claude-fable-5

What happened
A session spawned two background agents via the Agent tool (run_in_background: true). Both agents completed successfully and their task-notifications were delivered; TaskList returns "No tasks found", no cron/scheduled wakeups, no background shell processes. The turn ended normally (final text message, no pending tool calls).

Despite that, the session is persistently shown as "working" (spinner/active indicator) in the app UI.

What I tried

• Closed and reopened the session — still shows working
• Restarted the desktop app — still shows working

Expected
Session indicator should return to idle once the turn ends and all background tasks have completed.

Notes

• No tokens are being consumed; it appears to be a UI state issue only.
• Possibly related to completed background agents remaining "resumable": the stuck state appeared specifically in the session where background agents had run, right after they finished.