Resolve explicit replies before conversation ownership fallback

Shared provider conversations must not collapse per-case ownership. When multiple active cases share one SMS thread, resolve an explicit, unique case or workflow-step reference against eligible per-case owners before applying a conversation-level latest-message fallback. Otherwise, a human handoff on one case can incorrectly suppress automation on unrelated cases. Keep generic, conflicting, duplicate, and explicitly human-owned references fail closed, while preserving transactional locks and idempotency around candidate selection. This does not authorize cross-case continuation for ambiguous replies or bypass human takeover on the referenced case.

Applies when: several independently owned support cases share one provider conversation. Keywords: support routing SMS conversation ownership handoff attribution idempotency