Choosing "Accept plan and build on default permissions" sometimes do not make the agent start implementing the plan

### Describe the bug

Sometimes, when choosing "Accept plan and build on default permissions" after generating a plan, the agent will only go back to normal mode, but will not start implementing the plan.
I need to ask it manually, which I guess will use a premium request while it should not.
I use the model "gpt-5.4 (medium)", but I believe there was also the issue with gpt-5.3-codex.

### Affected version

GitHub Copilot CLI 1.0.3.

### Steps to reproduce the behavior

1. Choose the model gpt-5.4 (medium).
2. Go in plan mode.
3. Generate a plan.
4. When it's done, choose "Accept plan and build on default permissions".
5. Notice it doesn't start the implementation.

Since it doesn't always happen, retry multiple times (perhaps with `--allow-all-tools` as this is what I use to workaround bug #1875).

### Expected behavior

When choosing "Accept plan and build on default permissions", it should start building the implementation.

### Additional context

Operating system: Linux
Terminal: Alacritty
Shell: fish