Team agents go idle without responding or completing tasks

Bug Description

Team agents spawned via Task tool with team_name and run_in_background: true (and also foreground) repeatedly go idle without:

• Sending any messages back to team lead
• Completing their assigned tasks (TaskUpdate)
• Producing any visible output

Reproduction

1. Create a team with TeamCreate
2. Create tasks with TaskCreate
3. Spawn 3 agents via Task tool with team_name parameter, mode: "dontAsk", subagent_type set to custom agent types (dlaw:qa-testing-expert, dlaw:security-engineer, dlaw:devops-engineer)
4. Agents go idle immediately after spawning
5. Send messages via SendMessage asking them to report findings
6. Agents go idle again without responding
7. Tried shutting down and re-spawning as foreground agents — same behavior
8. Repeated across 6+ agents, all exhibited the same pattern

Expected Behavior

Agents should read the files specified in their task prompt, perform analysis, send findings back via SendMessage, and mark tasks completed via TaskUpdate.

Actual Behavior

Agents go idle (receive idle_notification) without taking any visible action. No messages sent, no tasks updated, no errors reported. This happened consistently across all agent types tested.

Environment

• Claude Code CLI
• Model: claude-opus-4-6
• Platform: macOS Darwin 25.3.0
• Multiple agent types affected (qa-testing-expert, security-engineer, devops-engineer)
• Team primitives (TeamCreate, TaskCreate, SendMessage) all appeared to work — agents just never responded

Workaround

Performed the review directly in the main conversation context instead of delegating to team agents.