Poetry.lock vs pyproject.toml: Safe rollback after schema change?

Integration between Poetry.lock and pyproject.toml

The goal is to revert a project to a known good dependency state after the schema in pyproject.toml has been altered. In practice, this means restoring an older poetry.lock and invoking poetry install to re‑install the exact package hashes recorded in that lockfile.

Key constraints:

• Poetry 1.x and 2.x use different resolver algorithms; a lockfile that was valid under one may be rejected by the other.
• Modifying dependency constraints in pyproject.toml without re‑running poetry lock can leave the resolver in a partially resolved state.
• Running poetry install after replacing the lockfile may trigger ResolutionImpossible errors if the newer constraints conflict with the old lockfile.

Unresolved questions:

• Does restoring an older poetry.lock and running poetry install always re‑establish the exact environment, regardless of the Poetry version?
• How does the 2.x resolver handle previously valid lockfile combinations when pyproject.toml has been updated?
• Is there a documented, safe sequence of commands that guarantees rollback integrity after schema changes?