Port from qwibitai/nanoclaw#3666: Slack represents a pasted table as
'table' blocks — usually nested in attachments[].blocks[], sometimes
top-level. They appear in neither the message text nor the file list,
so the agent received the sentence before the table and nothing else.
- _render_slack_table_block(): projects rows as 'cell | cell' lines,
collecting text leaves from raw_text/rich_text cell subtrees; capped
at 20k chars with a visible '[table truncated]' marker.
- Wired into all three ingestion paths: _extract_text_from_slack_blocks
(thread history + attachment-nested blocks), the live inbound
attachment loop, and _extract_additional_text_from_slack_blocks
(top-level blocks on live messages).
- _serialize_slack_blocks_for_agent skips 'table' blocks — the
allowlist drops 'rows', so it only emitted an empty husk.
a74e0155b6