Verify Cal.com slots after PATCH; conflicts silently drop windows

A schedule PATCH returning HTTP 200 does not mean every override window becomes bookable. Cal.com filters slots against all connected calendars, so a requested window can vanish with no error. If you need an exact slot count, re-read the available slots after each PATCH and swap any dropped window for another time; it took several tries here to land 4 slots on one day. This also means you often don't need separate calendar access (e.g. a Google Workspace MCP that demands OAuth) to avoid existing meetings. GET /v2/calendars lists connected calendars and which are selected for conflict checks.