scalable: reused state inherits every behavior attached to it#16
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The existing 'don't optimize away the domain object' bullet warns against reuse that deletes the domain object. Add its mirror: reuse that silently inherits a hidden behavior. Repurposing an existing status/flag/enum/column (e.g. trialing to mean 'migration bridge') fires everything that already reads that value — webhooks, crons, entitlement gates, billing/credit grants, UI branches, cleanup jobs — not just the one property you wanted. Enumerate consumers up front (grep every reader) instead of discovering them reactively one bug at a time, and verify by diffing the whole system's response, not just the fields you predicted would change.
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What
Adds one bullet to `commands/scalable.md`, right after "don't optimize away the domain object."
That existing bullet warns against reuse that deletes the domain object. This adds its mirror: reuse that silently inherits a hidden behavior.
Why
Repurposing an existing status / flag / enum / column to mean something new (e.g.
trialingto mean "currency-migration bridge") doesn't just carry the one property you want — it fires everything already wired to that value: webhooks, crons, entitlement gates, billing/credit grants, UI branches, cleanup jobs.Real case that motivated this: a subscription currency-migration reused Stripe's
trialingstatus purely to defer a charge./scalablecorrectly flagged two inherited behaviors (orphan-cancel, upgrade block) — but only reactively, after being prompted. A third —trialingsub creation emitting a$0invoice →invoice.paid→ a full plan-credit grant — went unnoticed until it had minted a duplicate month of credits for every migrated customer.The fix is mechanical, not conceptual: grep every consumer of the reused value up front and enumerate what each does, rather than validating the one behavior you wanted and discovering the rest one bug at a time. Plus a verification note: diff the whole system's response (side-effect tables, ledgers), not just the fields you predicted.