Slack mrkdwn has no table syntax — GFM pipe tables render as literal-pipe
noise with a raw |---|---| separator row. Wrap detected tables in ```
fences so they render as monospace preformatted text, and pad cells to
per-column max display width (East-Asian Wide / Full-width chars counted
as 2 columns) so columns stay aligned even with CJK content.
Tables already inside fenced code blocks are left untouched, and the
emitted fences carry no language tag so they compose with the
lang-tag-strip pass. This covers the plain-mrkdwn text path; the opt-in
rich_blocks path already renders native Block Kit table blocks.
Reapplied from #16648 by @kylezh — the original patched
gateway/platforms/slack.py, which was migrated to
plugins/platforms/slack/adapter.py in the plugin migration.
Fixes the non-rich_blocks table path described in #8552.
a7738796e1