ADR-001 — No in-module model-generation picker

Status: accepted (2026-08, backfilled from the Moonshine v2 design discussion).
Context: When Moonshine v2 appeared as a successor to the first streaming engine, one option was a selection mechanism inside the module choosing which model generation to run.
Decision: Rejected. A new model generation is a new cartridge behind the same seam, selected by the host via descriptors (and, once real, the staging step) — never by logic inside a cartridge. A cartridge must not contain "if not me, use the other one".
Consequences: Cartridges stay dumb and swappable; selection logic concentrates in exactly one place (host resolution, index.adoc "Selection"); version coexistence is a packaging concern, not a runtime branch.