-- Which CLI a mission runs on, and therefore which rootfs image its microVM
-- boots (per A6: one image per CLI, independently versioned).
--
-- NULL means "the default" rather than a specific CLI, so existing missions
-- keep their current behaviour without a backfill: the microVM path reads NULL
-- as the golden rootfs, and the container path ignores the column entirely.
--
-- No CHECK constraint listing the CLIs. The set of images is a property of the
-- NODES (which ones have been built there), not of the schema, and a constraint
-- here would have to be migrated every time an image is added while still not
-- guaranteeing the image exists anywhere. The node validates and reports a
-- missing image by name; a wrong value fails loudly at launch rather than
-- silently booting something else.
ALTER TABLE missions ADD COLUMN IF NOT EXISTS backend text;

COMMENT ON COLUMN missions.backend IS
  'CLI/rootfs backend for microvm runtime_kind (e.g. claude, kimi, glm). NULL = default image.';