Rename the experiment from SCOPED_INCLUDES to SCOPED_TASKFILES to better
reflect its expanded scope. This experiment now provides:
1. Variable scoping (existing): includes see only their own vars + parent vars
2. Environment namespace (new): env vars accessible via {{.env.XXX}}
With TASK_X_SCOPED_TASKFILES=1:
- {{.VAR}} accesses vars only (scoped per include)
- {{.env.VAR}} accesses env (OS + Taskfile env:, inherited)
- {{.TASK}} and other special vars remain at root level
This is a breaking change for the experimental feature:
- {{.PATH}} no longer works, use {{.env.PATH}} instead
- Env vars are no longer at root level in templates
Add new experiment flag TASK_X_SCOPED_INCLUDES for scoped variable
resolution in included Taskfiles. When enabled, variables from included
Taskfiles will be isolated rather than merged globally.
This is the first step towards implementing lazy DAG-based variable
resolution with strict isolation between includes.
