bash tool sync mode does not return stdout output

### 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 `` 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)

Start by reproducing the issue with the bash tool in mode="sync" using a command such as echo hello, then compare its result with mode="async" and read_bash. The work is done when synchronous execution returns the command's stdout to the agent while preserving the exit status.

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