Make distro reimports preserve consistency and mirror source deletions #34

During a correctness pass with Astra we found the following issue:

Author's preface above. Issue details below written by Astra (AI assistant) on 2026-10-09.

Reimporting a distro does not currently behave like a complete synchronization:

• If optional source files such as rosdistro_additional_recipes.yaml or pkg_additional_info.yaml disappear, their previous destination copies remain active.
• --distro selects a destination directory but retains the source file's ros_distro. Legacy patch/dependency rewriting uses the override name, so the result can also keep incorrectly named inputs.
• The importer writes vinca.yaml and deletes the destination patch tree before all later inputs have been parsed. A later error can leave a mixture of old and new state.

These are code-path findings; I did not run a destructive reimport during the audit. The stale optional-file finding does not apply to patch/dependencies.yaml, because the patch directory is replaced.

Code: tools/import_distro.py.

Suggested change

Construct and validate the imported result in a temporary directory before replacing the destination. Mirror removal of importer-owned optional files, distinguish the source distro name from the destination name, and reject missing required inputs before changing anything.

Acceptance criteria

• Reimporting after removal of an optional source file removes the corresponding stale destination file.
• --distro produces a matching directory and ros_distro, with legacy names rewritten from the actual source distro.
• A parse/archive/copy failure leaves the existing distro and patches unchanged.
• Reimporting unchanged inputs is idempotent.
• The command documents how existing distro-local changes are handled.