Only text (0) and announcement (5) channels accept a direct message — forum
(15) and media (16) require thread creation, so they're dropped from the
picker (they returned 'non-text channel'). Channels are also filtered by the
bot's effective VIEW_CHANNEL + SEND_MESSAGES, computed from role base perms and
channel overwrites (Discord's documented algorithm), with a safe fallback to
type-only filtering when the bot's roles can't be resolved.
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