[Bug] Named/teammate agent spawns silently never start when tmux capability probe passes but pane creation fails (Windows)

Bug Description
sub agents are frequently failing for me. they constantly just hang for hours and nothign returns. this has been happening a lot since opus 5

Environment Info

• Platform: win32
• Terminal: yes
• Version: 2.1.220
• Feedback ID: fa3b4218-927c-44fd-a672-0c63da814a8c

What happens: Spawned two subagents (x-code-reviewer, x-qa) via the Agent tool with well-scoped prompts. 45+ minutes later neither had returned a result or a task notification. TaskList showed "No tasks found" the whole time. Three SendMessage pings were accepted into their inboxes ("success": true) — so the agents existed — but produced no reply, not even a partial one when explicitly told to stop and answer immediately.

Impact: Silent, unbounded hang. There's no progress signal and no timeout, so the main thread either blocks indefinitely or abandons the work. I ended up doing the review inline, which took minutes and found a real bug the agents were spawned to catch. This is a recurring pattern across sessions, not a one-off.

Expected: either a result, a failure, or a timeout with partial output. At minimum, TaskList should show running agents so a hang is diagnosable, and SendMessage "delivered" shouldn't be indistinguishable from "the agent is alive and will respond".

Environment: Claude Code, Windows 11, model claude-opus-5[1m], project-defined subagents in .claude/agents/.