List Instance Health

Health for every integration in the subject's live set (TOS-2708).

One row per instance, carrying the filter bucket (ready / degraded / needs_attention / unknown), the healthy/affected split, and the typed failure detail — so the Connected list can render All / Needs attention / Degraded / Ready without deriving health from raw evidence itself.

subject_identity_id is the identity whose profile is being viewed, which is NOT always the caller: an owner reading an owned agent's Integrations tab must see the AGENT's connections. It matters because a per_caller instance holds one connection row per identity — scoping to the caller there would render the owner's own credential health under the agent's name. Same authority as /instances/installed-on/{identity_id}: self or an owner.

Batched on purpose: connections, rollups, tool rows, definitions and profiles are each one query for the whole page, never one per instance.