Hey, this is the current behavior by design. Plans are saved to the user’s home directory by default, not in the project.
There’s a built-in workaround. With the plan open, click Save to workspace. This will move the plan into the project directory .cursor/plans/ and tie it to the workspace.
Saving plans at the project level by default is a common request. You can vote here: Option to save Plans in project-level .cursor directory
Let me know if Save to workspace solves what you need.