Status: IN
Autocomplete (time decay), URL shortener (expiration), and payment (balance derivation) all defer computation to the read path, keeping writes simple and append-only at the cost of read-time complexity and latency.
Three independent systems chose lazy evaluation, suggesting write-simplicity is the dominant concern in pedagogical implementations
Depends on (SL): autocomplete-decay-is-read-time, url-shortener-expiration-lazy, payment-balance-never-cached