bash tool sync mode does not return stdout output

[quetsalkoatl]

Describe the bug

When the Copilot CLI agent uses the bash tool in mode="sync", it cannot read the stdout output of commands. Commands execute successfully (exit code 0) and the user can see the output in the terminal, but the agent only receives <exited with exit code 0> with no output content.

The same issue occurs with the Copilot Chat extension in VS Code.

This must be some configuration issue on my side because no one else I asked has this issue. I also have a huge convo with Claude where I was trying to fix this issue but in the end it recommended opening an issue here.

Affected version

GitHub Copilot CLI 1.0.12

Steps to reproduce the behavior

Ask the agent to run any shell command that produces output, e.g.:

"Run echo hello and tell me what it printed"

Expected behavior

The agent receives the stdout and can reference it in its response.

Additional context

Workaround

The agent can use mode="async" combined with read_bash to successfully retrieve output.

Environment

• OS: macOS (Tahoe 26.2)
• Affected: Copilot CLI v1.0.12, Copilot Chat VS Code extension (0.41.2)