pnpm pipeline runs nothing in a workspace whose only project is the root #16849

In a workspace whose only project is the root (packages: ['.'], or no packages key), pnpm pipeline and pnpm pipeline --full select no projects. They print "No projects are affected since origin/main — nothing to run." and exit 0. In the same workspace, pnpm -r run build runs the root's build script.

Reproduction (pnpm 12.12.1):

mkdir a && cd a && git init -q -b main
echo '{"name":"a","scripts":{"build":"echo BUILD"}}' > package.json
printf 'packages:\n  - .\npipelines:\n  default: [build]\n' > pnpm-workspace.yaml
pnpm install && git add -A && git commit -qm init
pnpm pipeline --full   # No projects are affected since origin/main — nothing to run.
pnpm -r run build      # BUILD

Expected: in a root-only workspace, the pipeline selects the root, the same way recursive commands do. Recursive commands skip their usual root exclusion when the root is the only project.

Setting includeWorkspaceRoot: true works around it. But the setting stays in place after the workspace gains other projects, and from then on it adds the root's tasks to every pipeline run.

Also, when --full selects nothing, the message still says "No projects are affected since ", which describes affected selection rather than a full run.

The pipeline docs say the root is excluded unless includeWorkspaceRoot is true. The fix should cover the root-only case there too.

Written by an agent (Claude Code, claude-opus-5-5).