Move tag validation before the UpdateNode callback in applyAuthNodeUpdate.
Previously, tag validation happened inside the callback, and the error
check occurred after UpdateNode had already committed changes to the
NodeStore. This left the NodeStore in an inconsistent state when tags
were rejected.
Now validation happens first, and UpdateNode is only called when we know
the operation will succeed. This follows the principle that UpdateNode
should only be called when we have all information and are ready to commit.
Also extract validateRequestTags as a reusable function and use it in
createAndSaveNewNode to deduplicate the tag validation logic.
Updates #3038
Updates #3048
d7f7f2c85e