The project code was locked once set, on the belief that changing it
would break joins. Nothing joins on it: every record links to the site by
id, and the PO email intake reads codes live. A mistyped code (Nellmapius
was 001 instead of C26/27) could only be fixed in the database.
In Edit site an admin double-clicks the code to unlock it. PATCH accepts
project_code from admins only, trims it, requires 1-64 characters, answers
409 when another site already uses it, and writes nothing when unchanged.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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