[smaugho]

Fixes #23752.

Problem

In a pnpm workspace, installing the node package for a target only installed that package's own dependencies. When the package depends on another workspace package, that package's dependencies were left uninstalled, so code importing through it failed at runtime (e.g. Cannot find package '@invented/leaf').

Change

When Pants installs a pnpm workspace member, it now selects the member together with its dependencies, using pnpm's <package>... filter, instead of the member alone.

• Only the pnpm install path changes. Ordinary commands, npm and yarn, root environments and single-package projects keep their current selectors.
• Release note added in docs/notes/2.34.x.md.

Tests

• New regression test: a workspace reader -> contract -> leaf. It installs through the real rules and runs Node. On current main without the fix it fails (Cannot find package '@invented/leaf'); with the fix Node prints 42.
• Scope cases cover installation versus ordinary commands across pnpm, npm and yarn, and member, root and single environments.
• Verified on main 05181fa with the native engine built locally: 25/25 tests in install_node_package_test.py and nodejs_project_environment_test.py, lint, MyPy, build-support/githooks/pre-push and pants --changed-since=HEAD fmt all pass.

AI disclosure

This PR was written primarily by Claude Code; I reviewed and tested it.