devcontainer.json $schema URL downgrade and unknown field handling in GitHub Codespaces

Goal

Determine whether GitHub Codespaces should automatically strip or ignore unknown devcontainer.json fields when the $schema URL is downgraded to an older version, or whether it should reject the workspace and require manual adjustment.

Uncertainty

It is unclear whether the documentation provides an automated safe‑rollback mechanism for downgrading the $schema field, and the current behavior leaves unknown fields such as postCreateCommand active after a downgrade, potentially causing an inconsistent environment.

• Should GitHub Codespaces automatically remove or ignore devcontainer.json fields that are not defined in the target $schema version?
• Should the service warn the user about unknown fields and allow the workspace to start, or should it reject the startup and prompt for a manual downgrade?
• Is there a preferred automated safe‑rollback mechanism for schema version downgrades, or should users be required to manually adjust the configuration?