Architecture - platform-achievements

Modules

Module	Role
`platform.ts`	The model: definitions, `resolveAchievements`, `outstanding`, and the adapter contract
`sync.ts`	`syncAchievements`: the only code that talks to an adapter and a store together
`store.ts`	The `AcknowledgementStore` interface and an in-memory implementation
`validate.ts`	Console limits and `validateAchievements`
`adapters/*.ts`	One file per platform, each depending on `platform.ts` types only
`export/*.ts`	Pure submission writers, one file per console, plus CSV and ZIP helpers

The root entry point re-exports platform, store, sync and validate. Adapters and export are separate entry points, so an app that ships only the Steam build never bundles the Play adapter.

Invariants

Nothing is queued. The only state is what the game has earned and what each platform has acknowledged. Outstanding work is a pure function of the two (outstanding).
Acknowledge after confirmation. syncAchievements records a value only after the adapter's call resolved, and a store never lowers a value.
Progress is absolute in the model and translated per platform inside the adapter (steps, percentage points, a stat).
No runtime dependencies and no platform imports. Adapters take structural interfaces. A change that imports Capacitor, a Play Games plugin or steamworks.js is wrong.
A failure is data. A refused report becomes an entry in SyncResult.errors; one failure never stops the rest and nothing throws out of syncAchievements for an adapter error.
Export is pure. Writers return strings and icon descriptions; the caller touches the file system and draws the icons.

Intentional limits

An add-only platform with a non-durable store gets unlocks only. Sending progress there would add the same steps again after a restart.
One sync at a time per platform. The store has no locking.
No tiers, repeatable achievements, or leaderboards. Tiered achievements are separate achievements.
No Play Console API calls. The Play ids come back through the resources file the console offers.