Cron jobs targeting a Slack user (deliver=slack:U…) failed with
channel_not_found: chat.postMessage and files_upload_v2 require a
conversation ID, and a DM must be opened first via conversations.open
to obtain a D… ID. The tool-level resolution in send_message() does not
cover cron's direct _send_to_platform → standalone_sender_fn path.
Add _resolve_slack_user_dm to the Slack plugin: resolves U…/W… targets
via conversations.open (proxy-aware, cached per token+user so repeated
cron fires don't re-open the DM), wired into _standalone_send ahead of
both the text and media delivery branches so every standalone entry
point benefits.
Adapted from #17444 by @Esther-Zhu023 — the original patched the legacy
_send_slack helper in tools/send_message_tool.py, which has since moved
into the plugin as _standalone_send (#41112).
Closes#17444
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
c7b9dfa961