Task tool subagent processes not terminating after completion (memory leak)

Description

The Task tool spawns subagent processes (claude --output-format stream-json) that don't terminate after the task completes. These orphaned processes accumulate over extended sessions, each consuming ~350MB of RAM.

Steps to Reproduce

1. Start a Claude Code session
2. Use the Task tool to spawn subagents (e.g., explore codebase, run background tasks)
3. After tasks complete, check for lingering processes:

``bash
ps -eo pid,ppid,etimes,args | grep 'output-format stream-json' | grep -v grep
``

Expected Behavior

Subagent processes should terminate cleanly when:

• The task completes and returns results to the parent
• The parent session closes the communication pipe

Actual Behavior

Subagent processes remain running indefinitely in Sl (sleeping, multi-threaded) state:

  66480    2513 Sl   /home/kron/.local/bin/claude --output-format stream-json --verbose --input-format stream-json --model claude-sonnet-4-5 --disallowedTools Bash,Read,Write,Edit,Grep,Glob,WebFetch,WebSearch,Task,NotebookEdit,AskUserQuestion,TodoWrite --setting-sources  --permission-mode default

The parent PID points to an unrelated daemon process, indicating the subagent was orphaned and re-parented by the OS.

Impact

• Memory leak: ~350MB per orphaned subagent
• After extended use with multiple Task tool invocations, several GB of RAM can be consumed
• Requires manual cleanup or cron-based workaround

Workaround

Cleanup script that kills subagents older than 5 minutes:

#!/bin/bash
MAX_AGE_SECONDS=300
mapfile -t PROCS < <(ps -eo pid,etimes,args 2>/dev/null | grep 'claude' | grep '\-\-output-format stream-json' | grep -v '\-\-dangerously-skip-permissions' | grep -v grep)
for proc in "${PROCS[@]}"; do
    read -r PID ELAPSED REST <<< "$proc"
    [[ "$ELAPSED" -gt "$MAX_AGE_SECONDS" ]] && kill "$PID" 2>/dev/null
done

Environment

• OS: Linux 6.8.12-18-pve
• Claude Code version: Latest (installed via npm)
• Model: claude-opus-4-5-20251101 (parent), claude-sonnet-4-5 (subagents)

Possible Cause

The Task tool may not be:

1. Sending SIGTERM to the subagent when the task completes
2. Properly closing stdin to signal EOF
3. Waiting for the child process to exit (zombie prevention)