Entities are global; facts are persona-scoped. Under the active
persona an entity can read as "0 facts" while having plenty under
other personas the user owns — the curation UI had no way to
surface that gap. Adds a batched DAO method
`get_persona_breakdowns_for_entities` that returns
{entity_id → [(persona_id, count)]} in one query (group by
subject + persona, user-scoped, status != rejected), and wires it
into both /knowledge/entities list rows and
GET /knowledge/entities/{id}.
EntitySummary grows an optional `persona_breakdown` field
(skipped on serialization when None — keeps PATCH responses
unchanged). EntityDetailResponse carries the breakdown as a
non-optional Vec since the detail endpoint always populates it.
One extra query per list page (50 entities → 50 subject ids
batched in one IN clause); single-entity GET adds one round trip.
Indexed by (subject_entity_id, persona_id) implicitly via the
existing user-persona indexes on entity_facts.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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