[BUG] Background task completion notification not appearing / activating Claude

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Bug Report: Background task completion notification not appearing

Title

[BUG] Background task completion notification not appearing on Windows and not activating Claude from idle state

Environment

• OS: Windows 11
• Claude Code version: (check with claude --version)
• Terminal: VS Code integrated terminal / Windows Terminal

Description

When running commands with run_in_background: true, the automatic completion notification (⏺ Background command "..." completed (exit code 0)) does not appear in the conversation and, more importantly, does NOT activate claude from idle state.

I use backgrounding often and have Claude idle (no sleep, no monitoring) waiting for the completed code that will awaken Claude to continue. This saves tokens.

Without the Background notification, Claude is required to actively monitor or for me to alert Claude that the background has finished.

Steps to Reproduce

1. Start a Claude Code session
2. Run a background command:

``
Bash(command="ask-agent --CWD='.' --AGENTS=g25l 'Reply: TEST'", run_in_background=true)
``

1. Wait for the task to complete (verify by checking the output file)
2. Expected: ⏺ Background command "..." completed (exit code 0) appears
3. Actual: No notification appears; must manually check with TaskOutput

Expected Behavior

When a background task exits, Claude Code should automatically inject the completion notification into the conversation, allowing the assistant to respond without polling.

Actual Behavior

• Task completes successfully
• Output file shows [DONE] message and exit code 0
• No automatic notification appears
• Must manually poll with TaskOutput to detect completion

Additional Context

• This worked previously (the feature exists per #18544)
• Multiple background tasks tested, none trigger notification
• Both stdout and stderr are being written by the command
• Process exits cleanly with code 0

Workaround

Currently must use TaskOutput(task_id="...", block=true) to wait for completion, which defeats the purpose of background tasks for parallel work.

What Should Happen?

Expected Behavior

When a background task exits, Claude Code should automatically inject the completion notification into the conversation, allowing the assistant to respond without polling.

Error Messages/Logs

Steps to Reproduce

Steps to Reproduce

1. Start a Claude Code session
2. Run a background command:

``
Bash(command="ask-agent --CWD='.' --AGENTS=g25l 'Reply: TEST'", run_in_background=true)
``

1. Wait for the task to complete (verify by checking the output file)
2. Expected: ⏺ Background command "..." completed (exit code 0) appears
3. Actual: No notification appears; must manually check with TaskOutput

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.19

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_