Fleet/agents view: "deleted" (Ctrl+X) background sessions get respawned by the daemon supervisor and become un-openable ("running in another terminal")

Describe the bug

In the claude agents (Fleet) view, deleting a session with Ctrl+X does not actually terminate the session. The daemon supervisor respawns the worker, so the session reappears in the Completed group after the view restarts. Because a live worker keeps holding the session lock, trying to open the reappeared session fails with:

Can't open — this session is running in another terminal

The result is a limbo state: sessions that appear in the list but can be neither opened nor removed. Over time the Completed list fills up with these zombie entries (I remembered ~5-6 agents, now many more show up).

Environment

• Claude Code version: 2.1.204
• Platform: macOS (darwin 25.5.0)

To reproduce

1. Launch several background agents from the Fleet view (claude agents).
2. Delete some of them with Ctrl+X (stop, then delete).
3. Restart / reopen the agents view.
4. The deleted sessions reappear in the Completed group.
5. Try to open one → Can't open — this session is running in another terminal.

Evidence (from ~/.claude/daemon/roster.json)

All 7 registered workers are alive (verified with kill -0). Three of them show "attempt": 2, i.e. the supervisor already respawned them at least once after they were stopped:

worker  attempt  pid
A        2        (alive)
B        2        (alive)
C        2        (alive)
D        1        (alive)
E        1        (alive)
F        1        (alive)
G        1        (alive)

Each worker's dispatch has "source": "fleet", launch.mode: "resume", respawnFlags: ["--agent","claude","--permission-mode","auto"]. The supervisor keeps them (or respawns them) even after a Ctrl+X delete, so killing the worker PID alone doesn't help — the supervisor brings it back.

Expected behavior

• Deleting a session from the Fleet view should terminate the underlying worker and prevent the supervisor from respawning it.
• A finished/deleted session should not be reported as "running in another terminal".
• There should be a way to fully clear a session from the Completed list without manually stopping the daemon supervisor.

Actual behavior

• Delete only hides the entry in-memory; the worker stays alive and is respawned, so the entry comes back and stays un-openable.

Notes

• Daemon supervisor pid holds the roster; the only reliable workaround found is to stop all claude processes AND the daemon supervisor, otherwise workers respawn.