FleetView freezes for ~6 minutes after exiting an agent chat (attachJob blocks input loop)

Summary

In the multi-agent FleetView (claude agents), entering an agent session and then returning to the FleetView list via arrow key causes the list to become completely unresponsive — neither mouse-click nor keyboard (arrows, j/k, Tab) selects any agent. Debug logs show [FV-attach] attachJob blocking for ~6 minutes before the list remounts, with a follow-up respawnJob failing because the prior session is still alive.

Environment

• Claude Code: v2.1.143 (npm-global install)
• OS: Windows 11 Pro for Workstations 10.0.26200
• Shell: PowerShell 5.1
• Terminal: legacy conhost (cmd.exe host) — TERM_PROGRAM=unset, TERM=unset
• Concurrent agents at time of repro: 4 working + 6 completed (10 total)

Reproduction

1. Run claude agents with several background agents already running.
2. Use arrow keys to highlight an agent in the FleetView list.
3. Press Enter to attach to that agent's session.
4. Use the arrow key (left arrow / Esc) to navigate back to the FleetView list.
5. Try to select another agent with mouse or keyboard → inert. No selection works.

The pane only recovers after either: a terminal resize, Ctrl+L, or restarting Claude Code entirely.

Hard evidence from --debug-file log

The smoking gun:

2026-05-17T14:39:11.963Z [DEBUG] [FV-attach] respawnJob 1675c4a4: ok=false alive=true err=Session 1675c4a4 is already running
2026-05-17T14:39:11.964Z [DEBUG] [PERF:bg-attach-start]
... (357 seconds of silence) ...
2026-05-17T14:45:11.367Z [DEBUG] [PERF:bg-attach-end]
2026-05-17T14:45:11.369Z [DEBUG] [FV-attach] attachJob returned after 359406ms — remounting list
2026-05-17T14:45:11.375Z [DEBUG] [PERF:bg-remount-start]
2026-05-17T14:45:11.414Z [DEBUG] [PERF:bg-remount-end]
...
2026-05-17T14:45:19.661Z [DEBUG] [FV-attach] respawnJob 3ed8e92a: ok=true alive=false err=

Two interleaved issues are visible:

1. attachJob blocks for 359,406 ms (~6 minutes) between bg-attach-start and bg-attach-end. During this window the FleetView UI is unresponsive — the input loop is waiting on this job.

2. Race condition on respawn: the first respawn fails with ok=false alive=true err=Session ... is already running. The lifecycle isn't cleaning up the prior attached session before respawn is attempted, so respawn no-ops and the UI is stuck holding a stale handle.

Why I think this is the root cause

The [PERF:bg-attach-*] and [FV-attach] events bracket the entire freeze window. There are no other long-running events in the log during those 6 minutes. Input handling appears to be coupled to the attach/respawn lifecycle, so when attachJob blocks, all selection input is dropped.

Related issues

These are adjacent but not duplicates:

• #58555 — FleetView layout broken after returning from session
• #59511 — Agent View opening hangs
• #30130 — Arrow keys ~1s input delay
• #35903 — CLI freezes when holding directional keys

Additional info

Debug log file (full, ~11KB) available on request — I can attach if helpful.

A second, separate bug surfaced in the same log: with TERM_PROGRAM=unset (legacy Windows conhost), synchronized output (DEC mode 2026) is disabled, causing 100% raw screen writes (blit=0, write=2181 at 51×209) per agent stream chunk. This produces the input-key lag many Windows users report (#30130, #35903) and is fixed by switching to Windows Terminal. If useful I can file that as a separate issue with a doc-only suggestion ("recommend Windows Terminal in the Windows install guide").