GET /api/insights/chat returns the caller's conversations newest-first
with cursor pagination (default limit 20, hard cap 50). Each row
carries id, title, timestamps, and a message count so the rail can
render without paying the per-message decrypt cost.
GET /api/insights/chat/[id] fetches one conversation with every
message decrypted in memory before serialisation. Provenance metadata
round-trips alongside the assistant turns.
DELETE /api/insights/chat/[id] hard-deletes the thread; the FK chain
cascades the message rows.
Cross-user lookups map to 404, never 403, so the existence channel
never leaks across accounts.
6 integration tests cover the list ordering, owner-only filter,
decryption round-trip, and the 404 boundary on both verbs.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
