ADR-0001 · accepted

Change the kit only where two genres or two apps show the need

Amended on 2026-11-06: GameDriver is gone; makeGameEngine's attach is the requestAnimationFrame adapter, see the note on ADR-0010.

Survivors shaped the kit alone, so nobody could tell which of its primitives were general and which only looked general (#4). The kit changes only where two genres, or two apps, show the same need (#4, restated in #27). A need that only one of them shows is recorded as a finding or an issue, and its code stays in that genre or app.

Consequences

• A genre writes its workaround first. The workaround moves into the kit once a second genre needs it. Push-puzzle's tile map stays in its genre package, and a direction-buttons input preset waits for a second grid game (finding 14).
• A shared-layer bug that makes a genre play wrong is fixed right away, unless the fix changes GameDefinition or GameEngine. A contract change gets its own issue (#4, #27).
• The kit's author can pick a shape early. PR #22 did that for #15, #16, #17 and #19, whose findings had left the shape to a third genre. Each fix is additive, so a genre that doesn't use it is unchanged.
• #23 follows the rule: each demo app builds its own save first. Whether a shared save package belongs in the kit is decided once both apps have one, and that answer becomes an ADR.
• Revisit if a follow-up needs a kit change that only one genre shows. #25 is the likely case: lockstep serves survivors' co-op, and push-puzzle uses it only if it gets the versus race that #25 suggests.