What changed

• Document that the host owns cwd and environment selection.
• Clarify that the kit performs generic ambient environment inheritance plus explicit overlay.
• Add a regression test proving product-specific variables are passed through unchanged by the generic kit.

Why

Filtering Tutti-specific variables inside the SDK would mix product policy into a reusable process library. The host must select the environment before invoking the kit.

Risks

No runtime behavior changes.

Verification

• pnpm typecheck
• env test suite, 16 tests
• pnpm build
• git diff --check