ADR 0254: Turn-based games share a play kernel

Status: accepted (VUH-1747, 2026-10-08).

Decision

Pokémon and Minecraft use one observe/decide/act/verify/remember scheduler in packages/play, extending ADR 0225 and ADR 0234. Game adapters supply observations, their native decision/action schemas, state fences, memory and progress policy. The kernel owns numbered turns and bounded proposal replacement; its model transport owns streaming, deadlines, cancellation and provider pricing. Neither adapter carries a second turn scheduler or pricing formula.

Minecraft's adapter and prompt live in integrations/minecraft. Pokémon retains its existing GbaDriverIo adapter in packages/play/free-play.ts, composed by integrations/pokemon. Moving files does not admit a second controller: core still owns leases, grants, join/leave, driver generations, model/persona resolution, recovery and room destinations. Minecraft's existing MCP motor and lifecycle remain separate. Full Minecraft lifecycle adoption and dynamic installed-extension registration under VUH-1616 remain follow-ups.

Policy stays explicit where the bodies differ. Both adapters allow at most two room-message replacements in a numbered turn. Pokémon aborts a proposal and reserves unreported usage; Minecraft lets its billed request settle first and stops when usage is unknown. Pokémon can re-decide a changed state twice within a turn; Minecraft records a stale turn and re-observes on the next turn. Their existing failure limits, action settlement, idle pacing and speech cooldowns remain adapter policy, using shared backoff/cooldown primitives.

Every new journal line carries the same run, journey, environment, session, venue, timestamp and version envelope (header V3; turn/summary/diagnostics V2). Native game payloads remain evidence, never authority. The existing reader accepts legacy Pokémon journals and projects Minecraft turns for evaluation, stories and journey memory, retaining native observations and exact action evidence. Pokémon scene/tile heuristics are unknown for Minecraft; absence of a Pokémon framebuffer, map or timing record is never filled with invented evidence. Bounded audience cards may truncate text; the canonical trail retains the native bounded payload. A separate read-only play environment identifier admits Minecraft metadata without expanding Pokémon's embodiment motor catalog.

Rivals is intentionally excluded. Its real-time tactical pad loop is owned by the Rivals controller (ADR 0175), not a slow turn-based model scheduler. This kernel does not prescribe routes, speech or actions, introduce a universal action schema, or change owner configuration. Verification uses existing game regressions and HTTP/model/voice/filesystem integration boundaries; it drives no live game body.