TaskOutput hangs after background agent completes

Problem Summary

When using TaskOutput to wait for a background task completion, the main session hangs and does not respond even after the agent has completed.

Steps to Reproduce

1. Start a background agent with Task(..., run_in_background=true)
2. Wait for results with TaskOutput(task_id) (with block=true)
3. Agent completes its work
4. Main session remains stuck in "Waiting for task" / "Booping…" state
5. More than 5 minutes pass without detecting completion
6. Manually cancel with Esc key, then the completed task's results are displayed

Expected Behavior

• TaskOutput should immediately return results when the agent completes
• Completion detection should work correctly

Actual Behavior

• TaskOutput continues to block after agent completion
• Session hangs in "Booping…" state for several minutes
• Results are only retrievable via manual cancellation (Esc)

Environment

• Claude Code version: 2.1.17
• Platform: Linux (WSL2)
• OS: Linux 6.6.87.2-microsoft-standard-WSL2

Additional Context

This issue significantly impacts workflows that rely on background agent orchestration. The workaround of manually canceling and re-requesting results is disruptive to automated pipelines.

Possible Root Cause

The completion polling/notification mechanism may not be correctly detecting when the background task state changes from "running" to "completed".