Bug Description

Fast shell commands like bare ls return empty stdout (exit code 0) even in non-empty directories. Slightly slower variants like ls -F (which stat()s each entry) return correct output.

Steps to Reproduce

1. Run Gemini CLI in ACP mode (--experimental-acp --yolo)
2. Ask: "exec ls command"
3. Observe: run_shell_command completes with exit code 0 but empty output
4. Ask: "exec ls -F command"
5. Observe: correct file listing is returned

Reproduces consistently in Docker containers (bun:1.2 base image) where node-pty is unavailable, forcing the child_process fallback path.

Root Cause

packages/core/src/services/shellExecutionService.ts line ~731 in childProcessFallback() uses:

child.on('exit', (code, signal) => {
  handleExit(code, signal);
});

Node.js documentation explicitly warns:

It is important to note that when the 'exit' event is triggered, child process stdio streams might still be open.

For very fast commands, the exit event fires before all stdout.on('data') callbacks have delivered pipe buffer contents to state.output. The close event waits for stdio streams to finish and is the correct event for this pattern.

Evidence from Timing

The 6ms difference (due to -F calling stat() per entry) is enough for the pipe buffer to flush before the exit handler runs.

Proposed Fix

Change child.on('exit', ...) to child.on('close', ...) at that line:

child.on('close', (code, signal) => {
  handleExit(code, signal);
});

The close event fires after all stdio streams are fully consumed, guaranteeing state.output contains the complete stdout/stderr data.

Environment

• Gemini CLI: installed via bun install -g @google/gemini-cli
• Runtime: Bun 1.2 in Docker (oven/bun:1.2)
• OS: Linux (Debian-based container)
• PTY: unavailable (no native build tools in container), falls back to child_process.spawn()
• Mode: ACP (--experimental-acp --yolo)

Notes

• PTY mode is likely unaffected since it writes to an xterm headless terminal buffer synchronously
• The cleanup() function inside handleExit does call stdoutDecoder.decode() for remaining bytes, but the issue is that stdout.on('data') events haven't fired yet, not that bytes are stuck in the decoder
• Related: #22170 and #23751 touched shell output buffering but not this specific race