Look up what a number supports

Ask what a phone number can receive, before you send to it. Works on any number in the world — it doesn't have to be one of your Dial numbers, and you don't have to have messaged it before. `supports` describes **the number you asked about**, not your own line. Each key is a channel, and the boolean says whether that number can be reached there. Today the only key is `imessage`; further channels arrive as further keys, so read the ones you care about by name rather than assuming the whole set. **The answer is point-in-time, not a property of the number.** `true` means the number is reachable on iMessage as of this request — someone who changes device or turns the service off stops being reachable, and the same number can answer differently next week. Treat it as a strong signal for picking a channel, not as a promise that a later send lands. **A lookup that fails is never reported as `false`.** If Dial can't complete the check the request fails with a `502`, so `false` always means "we asked, and the number isn't reachable there" — never "we couldn't find out".