Change which language the report and the AI plan will be written in.

The language is fixed when the address is handed out, because the SMTP connection that arrives ten minutes later carries no hint of who is waiting for it. That leaves one gap: somebody reserves an address, then switches the page to their own language before sending. Without this they would read a German page and get an English plan.

Only while the reservation is unused. Once the mail has arrived the analysis is either running or done, and rewriting the language then would mean re-running it — a different operation, and one nobody asked for.

The slug is the capability, as everywhere else here: whoever holds the address holds the test. There is nothing to leak — a wrong guess sets the language of a report the guesser cannot read.