Create Thread

Creates a new thread row.

WHO ACTUALLY CALLS THIS:

• mcp_server/admin/handlers/assistant.py (the admin MCP server at mcp.every.ai). External AI integrations like Claude.ai and ChatGPT invoke the ask_assistant MCP tool, which POSTs here to seed a thread before streaming agent output.

WHO DOES NOT:

• The web app (every-react) creates threads via a direct Supabase insert in packages/agent-chat/contexts/ThreadContext.tsx — RLS-protected.
• The mobile app (every-mobile-app) does the same in src/stores/threadStore.ts.

storage_mode is always "session"; the threads table column has the same NOT NULL default, so direct Supabase inserts land on the same value.

Idempotency: protected by idempotency_guard so MCP retries don't create duplicate threads. The MCP server doesn't send X-Idempotency-Key today but the guard is in place for future retry logic.