Widen the #19237 send_message fix to the live adapter: send, _upload_file,
send_multiple_images, send_image, send_video, send_document,
send_exec_approval, send_slash_confirm, and send_clarify now route bare
Slack user IDs (U.../W...) through a shared _ensure_dm_conversation helper
before calling chat.postMessage / files_upload_v2, which reject user IDs.
This closes the gap in #17261 where an attachment worked when replying in
a thread but failed when directed at a user DM, and extends the DM-open
fallback to clarify/approval Block Kit prompts so gated actions can reach
a user directly.
Resolution uses the workspace-scoped client (multi-workspace installs open
the DM with the right bot token), caches per (team, user), and records the
opened D... channel in the channel→team map. On failure the original
target passes through so the downstream API call surfaces the real Slack
error.
Fixes#17261
Refs #19236
Teknium
994a405f2d