The plan register has had this since 2026_07_30_110000. The module register
never did, so two rows could claim one Price and archiving the one would have
withdrawn the Price the other was still selling — Block D of the real-run
handoff.
It is also the net under the adoption step: at a VAT rate of nought both
treatments charge the same amount, and the check that refuses an already-claimed
Price is then the only thing keeping the two apart.
Duplicates are deleted, not archived. An archived row goes on claiming the id
and a unique index knows nothing about archived_at; the row rebuilds itself on
the next ensure(), and subscription_addons holds the Stripe id as text rather
than a foreign key, so no booking loses its price.
AddonPrices::remember()'s catch comment described the guard as the only thing
standing between two rows and one Price; now that the index exists, rewritten
to describe it as the net under that guard instead.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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