[Bug] KillShell tool terminates entire Claude instance in Docker containers

Bug Description
Bug Report: KillShell tool terminates entire Claude instance in Docker containers

Version: Claude Code 2.0.76

Environment: Docker container using node:20-bookworm-slim base image with dumb-init as entrypoint

Severity: Critical - causes complete instance termination

Description

When running Claude Code inside a Docker container, using the KillShell tool on any background process terminates not just the target process, but the entire Claude instance.

Steps to Reproduce

1. Run Claude Code in a Docker container with this setup:

FROM node:20-bookworm-slim
RUN apt-get update && apt-get install -y dumb-init
RUN npm install -g @anthropic-ai/claude-code
ENTRYPOINT ["dumb-init", "--", "claude", "--dangerously-skip-permissions"]

1. Start any background process:

node -e "setInterval(() => {}, 1000)" &

1. Use the KillShell tool on the background shell ID

1. Result: Entire Claude instance terminates, returning to host shell

Investigation Findings

Manual process killing works correctly and does NOT crash the instance:

• kill -TERM $PID works correctly
• kill -KILL $PID works correctly
• kill -TERM -$PGRP (process group kill) works correctly

Process isolation is correct:

• Background processes are properly reparented to dumb-init (PID 1)
• Process groups and session IDs are correctly separated
• dumb-init signal forwarding is working as expected

Conclusion: The bug is in the KillShell tool's internal implementation, not in container signal handling or process management.

Workaround

Use manual bash kill instead of KillShell:

kill $PID

Additional Context

• Bug does NOT occur when running Claude Code outside Docker containers
• Reproducible across multiple container configurations (tested with three separate Dockerfiles)
• All containers use identical setup: dumb-init -> start.sh -> exec claude

Environment Info

• Platform: linux
• Terminal: wsl-Ubuntu
• Version: 2.0.76
• Feedback ID:

Errors

[{"error":"Error\n    at ry (/$bunfs/root/claude:58:1144)\n    at <anonymous> (/$bunfs/root/claude:59:10093)\n    at emit (node:events:92:22)\n    at endReadableNT (internal:streams/readable:862:50)\n    at processTicksAndRejections (native:7:39)\n    at request (/$bunfs/root/claude:61:2149)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-05T01:32:05.289Z"},{"error":"Error: NON-FATAL: Lock acquisition failed for /home/jonnymanchild/.local/share/claude/versions/2.0.76 (expected in multi-process scenarios)\n    at W3$ (/$bunfs/root/claude:2427:2165)\n    at TTA (/$bunfs/root/claude:2427:1885)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-05T01:32:05.868Z"},{"error":"Error\n    at ry (/$bunfs/root/claude:58:1144)\n    at <anonymous> (/$bunfs/root/claude:59:10093)\n    at emit (node:events:92:22)\n    at endReadableNT (internal:streams/readable:862:50)\n    at processTicksAndRejections (native:7:39)\n    at request (/$bunfs/root/claude:61:2149)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-05T01:32:06.533Z"},{"error":"Error\n    at ry (/$bunfs/root/claude:58:1144)\n    at <anonymous> (/$bunfs/root/claude:59:10093)\n    at emit (node:events:92:22)\n    at endReadableNT (internal:streams/readable:862:50)\n    at processTicksAndRejections (native:7:39)\n    at request (/$bunfs/root/claude:61:2149)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-05T01:32:41.357Z"},{"error":"Error\n    at ry (/$bunfs/root/claude:58:1144)\n    at <anonymous> (/$bunfs/root/claude:59:10093)\n    at emit (node:events:92:22)\n    at endReadableNT (internal:streams/readable:862:50)\n    at processTicksAndRejections (native:7:39)\n    at request (/$bunfs/root/claude:61:2149)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-05T01:33:16.156Z"},{"error":"Error: Request was aborted.\n    at _createMessage (/$bunfs/root/claude:455:3157)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-05T01:34:03.641Z"},{"error":"Error\n    at ry (/$bunfs/root/claude:58:1144)\n    at <anonymous> (/$bunfs/root/claude:59:10093)\n    at emit (node:events:92:22)\n    at endReadableNT (internal:streams/readable:862:50)\n    at processTicksAndRejections (native:7:39)\n    at request (/$bunfs/root/claude:61:2149)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-05T01:34:29.619Z"},{"error":"Error: Request was aborted.\n    at _createMessage (/$bunfs/root/claude:455:3157)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-05T01:40:31.593Z"},{"error":"Error\n    at ry (/$bunfs/root/claude:58:1144)\n    at <anonymous> (/$bunfs/root/claude:59:10093)\n    at emit (node:events:92:22)\n    at endReadab

Note: Error logs were truncated.