Personal space is silently not created when another space already uses its ID #3943

With the decomposed driver, a user's personal space uses the user's ID as its space ID. If another space already has that ID, creating the personal space fails with ALREADY_EXISTS. The proxy calls CreateHome on every authenticated request and treats ALREADY_EXISTS as "the personal space is there", so it ignores the error without logging anything. The user ends up without a personal space, and nothing in the logs says why.

Today this can't happen, because project spaces get random IDs. It becomes possible once clients can choose the ID of a new space (#3899).

Expected

Creating a personal space fails with a distinct error (and a log line) when the ID is taken by a space that isn't this user's personal space, instead of the same ALREADY_EXISTS as when the user's own personal space already exists.

Where

• decomposed's CreateStorageSpace returns ALREADY_EXISTS whenever a space root with that ID exists, regardless of its type and owner.
• The proxy (services/proxy/pkg/middleware/create_home.go) only logs statuses other than ALREADY_EXISTS.