fix(discord): auto-convert markdown tables to bullet groups

[yashiels]

Summary

Discord does not render GFM pipe tables — raw pipe characters display as garbage text. This PR adds automatic table-to-bullet conversion in the Discord adapter's format_message, matching the pattern Telegram already uses.

Changes

1. Shared helpers (gateway/platforms/helpers.py)

• Added TABLE_SEPARATOR_RE, is_table_row, split_markdown_table_row, _render_table_block, and convert_table_to_bullets
• Same alignment logic as Telegram's proven renderer: non-row-label tables keep data_cells = cells and skip the duplicate-heading bullet

2. Discord adapter (plugins/platforms/discord/adapter.py)

• format_message now calls convert_table_to_bullets() instead of returning content as-is

3. Telegram DRY (gateway/platforms/telegram.py)

• Replaced local _TABLE_SEPARATOR_RE, _is_table_row, _split_markdown_table_row with imports from shared helpers
• Telegram-specific MarkdownV2 rendering (_render_table_block_for_telegram, _wrap_markdown_tables) stays local

Before / After (Discord)

Before: Raw pipe characters render as unreadable garbage:

| Model | Speed | Cost |
|-------|-------|------|
| GPT-4 | Slow | $$$ |

After:

**GPT-4**
• Speed: Slow
• Cost: $$$

Tests

• 18 new tests for shared helpers (tests/gateway/test_table_helpers.py)
• 4 new tests for Discord formatting (tests/gateway/test_discord_format.py)
• All existing Telegram format tests pass unchanged (34 total across all 3 files)

Edge Cases Handled

• Tables inside fenced code blocks are left untouched
• Plain text with pipe characters passes through unchanged
• Horizontal rules (---) are not mistaken for table separators
• Row-label columns (data rows with one more cell than header) detected correctly
• Bare pipe tables (no outer |) supported
• Multiple consecutive tables converted independently

Fixes #21168

[yashiels]

Rebased onto latest main (2026-06-18).

Approach note: This PR converts GFM tables to bold-heading + bullet groups rather than code fences. In practice, bullet groups read much better in Discord (especially mobile) than monospace code blocks for tabular agent output. Happy to pivot to code-fence wrapping if maintainers prefer that approach — the shared helpers in helpers.py would still be useful either way.

Conflict resolution: kept upstream's rich_messages=True default in telegram.py; this PR only deduplicates table-detection primitives into the shared module.

[yashiels]

Rebased onto latest main — merge conflicts resolved, CI should be green.

No CODEOWNERS file in repo; tagging Discord/gateway maintainers for review:

@teknium1 @kshitijk4poor — would appreciate a look when you have a moment.

Summary: Converts markdown tables to bullet groups in Discord format_message() (Telegram-style). Shared helpers extracted to gateway/platforms/helpers.py. Fixes #21168.

Happy to pivot to code-fence wrapping if that's the preferred approach — bullets read better on Discord mobile in our testing.

[kshitijk4poor]

Merged via #53284. Your commits were cherry-picked with authorship preserved (rebase-merge) onto latest main. The original branch was 1086 commits behind, and Telegram had migrated from gateway/platforms/telegram.py to plugins/platforms/telegram/adapter.py since your base — resolved the conflict and also completed the DRY refactor you started (deleted the duplicated renderer+driver from Telegram that were verbatim copies of the shared helpers). Your 3 commits + 1 follow-up fix landed in commit 6326d5c.

Thanks for the contribution!