Widen #48476's fence guarantees to the two splitters that still emitted
fence-broken chunks:
* GatewayStreamConsumer._split_text_chunks (fallback final send): close
the orphaned ``` at each chunk boundary and reopen it — with the
original language tag — on the next chunk, mirroring
BasePlatformAdapter.truncate_message's contract. Headroom is reserved
so balanced chunks stay within the platform limit.
* Slack block_kit._split_text (3000-char section chunking): same
close/reopen balancing for mrkdwn section text carrying fences.
With these, every chunk boundary — non-streaming send
(truncate_message), streaming overflow (_truncate_for_stream via
adapter.truncate_message per #45938), fallback final
(_split_text_chunks), final-send balance (ensure_closed_code_fences),
and Block Kit section splits — delivers fence-balanced chunks.
Regression tests probe each path with fenced fixtures, assert per-chunk
balance, limit compliance, language-tag reopening, and prose passthrough.
Slack rejects a rich_text_section / rich_text_preformatted / rich_text_quote
whose elements list is empty or contains a zero-length text element, and a
header whose plain_text is empty. The Block Kit renderer emits exactly those
shapes for common inputs: a markdown table with a blank cell or a ragged
(short) row, an empty fenced code block, a blank quote line, an empty list
item, and an emphasis-only header ("# ***"). Any one of them poisons the
whole payload — chat.postMessage fails with invalid_blocks ("missing element"
/ "must be more than 0 characters") and the message loses its rich rendering
entirely.
Route every rich_text builder's child elements through _nonempty_elements
(drop zero-length text elements; substitute a single space when nothing
remains) and skip headers that reduce to empty after markdown-marker
stripping. Observed in production via live chat.postMessage rejections;
regression tests cover each case plus a well-formed-content control.
Complementary to #56618 (column_settings hardening + no-blocks retry): that
change makes Block Kit rejections recoverable, this one makes the common
empty-content cases render correctly in the first place. No overlapping hunks.
Refine the blank-line handling so a blank line only continues a list run
when the next non-blank line is another list item. This keeps a list ->
paragraph -> list sequence as three separate blocks and matches the
contiguous-list layout for mixed/nested lists (one rich_text block, split
into sub-lists by (indent, ordered)), rather than emitting a separate
block per item.
Adds regression tests for the mixed blank-separated layout and the
list->paragraph->list boundary.
When a Markdown ordered list has blank lines between items (common in
LLM-authored content), the list run loop breaks on each blank line.
Slack numbers each rich_text_list independently, so N items produce N
lists each starting at 1.
Skip blank lines inside the list run as soft separators instead of
breaking, so ordered items stay in one rich_text_list and Slack renders
the correct numbering.
Fixes#57076
Replace the interim monospace table fallback with Slack's native `table`
block (rows of rich_text cells). Addresses the core ask in #18918.
- _table_block(): builds type:"table" with rich_text cells, so inline
formatting (bold, links, code) renders inside cells.
- Column alignment parsed from the markdown separator row (:---, :-:, --:)
into column_settings (left = default/null-skip, center/right emitted).
- Escaped pipes (\\|) are not treated as column separators.
- Respects Slack's table limits (100 rows / 20 cols / 10k aggregate chars);
oversized or unparseable tables gracefully fall back to aligned monospace
(rich_text_preformatted), so a big table never breaks the message.
Docs (EN + zh-Hans) updated to describe native tables + the fallback.
Tests: native table shape, alignment->column_settings, inline-formatted
cells, oversized/too-wide monospace fallback, escaped-pipe cell. Prove-
failed against a stubbed _table_block (native-table tests fail, fallback
tests stay green). All existing Slack tests still pass.
Add platforms.slack.extra.rich_blocks (default off). When enabled, the
final agent message is sent as Slack Block Kit blocks — section headers,
dividers, and true nested lists via rich_text — instead of flat mrkdwn.
- New plugins/platforms/slack/block_kit.py: pure markdown->blocks renderer
(headers, dividers, nested ordered/bullet lists, blockquotes, fenced code;
pipe-tables as aligned monospace since Block Kit has no robust table block).
Enforces Slack's 50-block / 3000-char section limits and returns None to
fall back to plain text on empty/oversized/unexpected input. Never raises.
- adapter.send(): render blocks on the single-chunk primary message; a
text= fallback is ALWAYS sent alongside (notifications/accessibility).
- adapter.edit_message(): blocks only on finalize=True, so intermediate
streaming edits stay plain mrkdwn (no per-flush block re-derivation).
- Docs (EN + zh-Hans) + config example. Send-side only: no app reinstall.
Tests: pure-renderer unit suite + adapter integration suite (blocks present
when on, plain text when off, text fallback always set, finalize gating,
multi-chunk fallback). Prove-failed against a stubbed renderer.
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