Direct package installs bypass PM's dependency selection and do not survive
new generations. Document explicit runtime extras, recorded repair, fresh
build outputs, and lock generation through PM instead.
Keep the prepared-interpreter prerequisite and explicit removal requirement
for disposable test environments. Preserve Nix and external-project package
manager ownership. Correct platform and Python-marker claims where the
manifest contradicts the installation hints.
Checked the public CLI help, literal PM calls against public signatures and
extra declarations, fenced blocks, and whitespace. No dependency build or
site build ran. The docs toolchain is not installed in this checkout.
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