Cache the emoji set.

codemojex validates every guess against the round’s emoji set. Codemojex.Guesses.submit/3 turns an untrusted guess into a branded JOB on the player’s lane or one closed error, and one of the first checks is the keyboard: it calls Codemojex.Cache.fetch_set(set_id) and runs EmojiSet.valid_guess?/2, answering {:error, :bad_guess} for a code the round’s keyboard does not expose. That emoji set lookup is reference data — read on every guess, immutable for the round’s life — which is exactly the read-heavy, write-light shape cache-aside is built for. Fronting it with EchoStore.Table is the workshop.

The read path stacks four layers, each adding one move taught earlier in the chapter, and each leaving the read correct on its own. The base layer is a cache-aside read: EchoStore.Table.fetch/3 checks L1 ETS, then on a miss runs a single-flight fill — GET ecc:{cm_emojisets}:<id>, the loader, then SET … PX — and returns {:ok, value, source} with source :hit | :l2 | :fill. The next layer keeps the cache consistent: a room’s emoji set changing runs Coherence.broadcast/4 on the fast lane or Coherence.enqueue/5 on the at-least-once job lane, and Coherence.newer?/2 resolves a late message newer-wins.

The third layer hardens the set every guess touches — EchoStore does this by construction: the single-flight flights map coalesces a herd onto one fill, and a jittered TTL (ttl ± ttl·jitter) keeps a cohort from expiring together. The fourth layer measures: EchoStore.Table.stats/1 returns the counter snapshot — hits, misses, fills, l2_hits, coalesced, swept, full_skips, sweeps, coh_applied, coh_stale plus live size — so the hit rate is a number, not a guess. Nothing here is new: each layer is a pattern from R1.01–R1.06, applied to one real surface. The work is the assembly.

The workshop is three dives. Each takes one layer and builds it on the real consumer surface, ending with the read path one step closer to production. Take them in order: the cache must exist before it can be kept consistent, and it must be consistent before its hit rate means anything.

Pick a stage to see which EchoStore surface it adds to the read path and what the cache can do once it lands. The surface grows as the stages stack; the readout names the new calls and the property the layer secures.