@ file autocomplete filtering broken inside Docker container (devcontainers CLI)

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?

When running Claude Code inside a Docker container via devcontainers CLI (without VS Code), the @ file autocomplete shows the file list initially, but typing any character to filter causes the list to disappear completely.

Key observations:

• Typing @ alone correctly displays the file list (e.g., CLAUDE.md, docs/, .devcontainer/)
• Typing @C or any other character causes the entire list to vanish
• The / command autocomplete works correctly with filtering
• fzf filtering works correctly in the same terminal session
• ripgrep (rg --files) works correctly
• This issue does not occur when running Claude Code directly on macOS host

What Should Happen?

When typing @C, the file list should filter to show files starting with "C" (e.g., CLAUDE.md).

Steps to Reproduce

1. Set up a devcontainer with the following Dockerfile:

FROM node:20-bookworm-slim

RUN apt-get update && apt-get install -y \
    git curl sudo ca-certificates ripgrep \
    && rm -rf /var/lib/apt/lists/*

ARG USERNAME=node
RUN echo "$USERNAME ALL=(ALL) NOPASSWD:ALL" >> /etc/sudoers

RUN mkdir -p /workspace /home/node/.claude \
    && chown -R node:node /workspace /home/node/.claude /home/node

ENV DEVCONTAINER=true
ENV TERM=xterm-256color
WORKDIR /workspace
USER node

RUN curl -fsSL https://claude.ai/install.sh | bash
ENV PATH="/home/node/.claude/bin:/home/node/.local/bin:$PATH"

1. Create devcontainer.json:

{
    "name": "Claude Code Sandbox",
    "build": { "dockerfile": "Dockerfile", "context": "." },
    "mounts": [
        "source=claude-config-${localWorkspaceFolderBasename},target=/home/node/.claude,type=volume"
    ],
    "workspaceFolder": "/workspace",
    "remoteUser": "node"
}

1. Start container using devcontainers CLI (not VS Code):

devcontainer up --workspace-folder .
devcontainer exec --workspace-folder . bash
# or
docker exec -it <container_id> bash

1. Initialize git and create a file:

git init
echo "# Test" > CLAUDE.md

1. Run Claude Code and try @ autocomplete:

claude
# Type: @      -> File list appears correctly
# Type: @C     -> File list disappears

Environment Info

• Platform: Linux (Docker container on macOS host)
• Base image: node:20-bookworm-slim (Debian Bookworm)
• Terminal: Ghostty 1.2.3 on macOS
• Claude Code Version: 2.1.27
• Container access method: devcontainers CLI / docker exec -it

Troubleshooting Attempted

• ✅ fzf filtering works correctly in the container
• ✅ System ripgrep works correctly (rg --files returns expected results)
• ✅ USE_BUILTIN_RIPGREP=0 claude - no change
• ✅ Set LANG=en_US.UTF-8 and LC_ALL=en_US.UTF-8 - no change
• ✅ Set COLORTERM=truecolor and TERM_PROGRAM=ghostty - no change
• ✅ / command autocomplete works correctly with filtering

Additional Context

• Works correctly on macOS host with the same terminal (Ghostty)
• Only broken inside Docker container
• The @ displays the initial list, proving file indexing works
• Only the filtering/fuzzy search functionality is broken

Related Issues

• #11902 - File completion filters using wrong directory (similar symptoms but different root cause)
• #14399 - @ path autocomplete broken in container (different symptom: wrong path prefix)
• #5559 - File Reference Autocomplete Fails with Partial Filename Input (closed)