Issue Summary

The Confluence Cloud Migration Assistant pre-migration checks only validate against the current, active space keys on the destination site. They do not evaluate space aliases (older keys a space previously used, often left behind by earlier test migrations or renamed/recreated spaces).

As a result, a space whose current key matches an alias already registered on a destination space passes validation cleanly, but then fails at import time with a space key/alias conflict. The conflict is only surfaced once the migration runs, not during validation when it could still be resolved.

Example scenario (Confluence Cloud-to-Cloud):

A source space has an active key of KEY-A but historically used the key KEY-B.
A destination space (current key KEY-C) has KEY-B registered as an alias.
The source KEY-B key collides with the destination KEY-B alias, causing the import of that space to fail — even though the destination space was never part of the migration scope.

Steps to Reproduce

1. On the destination Cloud site, have a space whose current key differs from an alias it holds (commonly left over from a prior test migration or a renamed/recreated space).
2. Set up a Confluence Cloud-to-Cloud migration for a source space whose key (current or historical) equals that destination alias.
3. Run the pre-migration checks / validation stage. The space key conflict check passes (green) because no current destination key matches.
4. Run the migration.

Expected Results

The pre-migration space key conflict check detects the collision between the source space key and the destination space alias and flags it during validation, so it can be resolved before the migration is run.

Actual Results

Validation passes with no conflict reported, but the space fails to import during the migration run. The failed space is reported as conflicting with a destination space/alias that was never selected as part of the migration scope.

The below exception is thrown in the migration log:

A space with key <destination-space-key> already exists in the destination site.
That existing space has alias <conflicting-alias>.
Because of that conflict, the import for space <source-space-key> could not complete.
Status code: 516

Workaround

On the destination site, remove or rename the conflicting space/alias before retrying, or export the affected space from the source and import it into a brand-new space with a non-conflicting key, then retry the migration for that space only.