fix(slack): comprehensive mrkdwn formatting — 6 bug fixes + 52 tests

Fixes blockquote > escaping, edit_message raw markdown, ***bold italic***
handling, HTML entity double-escaping (&), Wikipedia URL parens
truncation, and step numbering format. Also adds format_message to the
tool-layer _send_to_platform for consistent formatting across all
delivery paths.

Changes:
- Protect Slack entities (<@user>, <https://...|label>, <!here>) from
  escaping passes
- Protect blockquote > markers before HTML entity escaping
- Unescape-before-escape for idempotent HTML entity handling
- ***bold italic*** → *_text_* conversion (before **bold** pass)
- URL regex upgraded to handle balanced parentheses
- mrkdwn:True flag on chat_postMessage payloads
- format_message applied in edit_message and send_message_tool
- 52 new tests (format, edit, streaming, splitting, tool chunking)
- Use reversed(dict) idiom for placeholder restoration

Based on PR #3715 by dashed, cherry-picked onto current main.

gateway/platforms/slack.py

@@ -281,6 +281,7 @@ class SlackAdapter(BasePlatformAdapter):
                 kwargs = {
                     "channel": chat_id,
                     "text": chunk,
+                    "mrkdwn": True,
                 }
                 if thread_ts:
                     kwargs["thread_ts"] = thread_ts
@@ -323,9 +324,7 @@ class SlackAdapter(BasePlatformAdapter):
         if not self._app:
             return SendResult(success=False, error="Not connected")
         try:
-            # Convert standard markdown → Slack mrkdwn
             formatted = self.format_message(content)
-
             await self._get_client(chat_id).chat_update(
                 channel=chat_id,
                 ts=message_id,
@@ -457,13 +456,36 @@ class SlackAdapter(BasePlatformAdapter):
         text = re.sub(r'(`[^`]+`)', lambda m: _ph(m.group(0)), text)
 
         # 3) Convert markdown links [text](url) → <url|text>
+        def _convert_markdown_link(m):
+            label = m.group(1)
+            url = m.group(2).strip()
+            if url.startswith('<') and url.endswith('>'):
+                url = url[1:-1].strip()
+            return _ph(f'<{url}|{label}>')
+
         text = re.sub(
-            r'\[([^\]]+)\]\(([^)]+)\)',
+            r'\[([^\]]+)\]\(([^()]*(?:\([^()]*\)[^()]*)*)\)',
-            lambda m: _ph(f'<{m.group(2)}|{m.group(1)}>'),
+            _convert_markdown_link,
             text,
         )
 
-        # 4) Convert headers (## Title) → *Title* (bold)
+        # 4) Protect existing Slack entities/manual links so escaping and later
+        #    formatting passes don't break them.
+        text = re.sub(
+            r'(<(?:[@#!]|(?:https?|mailto|tel):)[^>\n]+>)',
+            lambda m: _ph(m.group(1)),
+            text,
+        )
+
+        # 5) Protect blockquote markers before escaping
+        text = re.sub(r'^(>+\s)', lambda m: _ph(m.group(0)), text, flags=re.MULTILINE)
+
+        # 6) Escape Slack control characters in remaining plain text.
+        # Unescape first so already-escaped input doesn't get double-escaped.
+        text = text.replace('&amp;', '&').replace('&lt;', '<').replace('&gt;', '>')
+        text = text.replace('&', '&amp;').replace('<', '&lt;').replace('>', '&gt;')
+
+        # 7) Convert headers (## Title) → *Title* (bold)
         def _convert_header(m):
             inner = m.group(1).strip()
             # Strip redundant bold markers inside a header
@@ -474,34 +496,39 @@ class SlackAdapter(BasePlatformAdapter):
             r'^#{1,6}\s+(.+)$', _convert_header, text, flags=re.MULTILINE
         )
 
-        # 5) Convert bold: **text** → *text* (Slack bold)
+        # 8) Convert bold+italic: ***text*** → *_text_* (Slack bold wrapping italic)
+        text = re.sub(
+            r'\*\*\*(.+?)\*\*\*',
+            lambda m: _ph(f'*_{m.group(1)}_*'),
+            text,
+        )
+
+        # 9) Convert bold: **text** → *text* (Slack bold)
         text = re.sub(
             r'\*\*(.+?)\*\*',
             lambda m: _ph(f'*{m.group(1)}*'),
             text,
         )
 
-        # 6) Convert italic: _text_ stays as _text_ (already Slack italic)
+        # 10) Convert italic: _text_ stays as _text_ (already Slack italic)
-        #    Single *text* → _text_ (Slack italic)
+        #     Single *text* → _text_ (Slack italic)
         text = re.sub(
             r'(?<!\*)\*([^*\n]+)\*(?!\*)',
             lambda m: _ph(f'_{m.group(1)}_'),
             text,
         )
 
-        # 7) Convert strikethrough: ~~text~~ → ~text~
+        # 11) Convert strikethrough: ~~text~~ → ~text~
         text = re.sub(
             r'~~(.+?)~~',
             lambda m: _ph(f'~{m.group(1)}~'),
             text,
         )
 
-        # 8) Convert blockquotes: > text → > text (same syntax, just ensure
+        # 12) Blockquotes: > prefix is already protected by step 5 above.
-        #    no extra escaping happens to the > character)
-        # Slack uses the same > prefix, so this is a no-op for content.
 
-        # 9) Restore placeholders in reverse order
+        # 13) Restore placeholders in reverse order
-        for key in reversed(list(placeholders.keys())):
+        for key in reversed(placeholders):
             text = text.replace(key, placeholders[key])
 
         return text

tests/gateway/test_slack.py

@@ -619,6 +619,18 @@ class TestFormatMessage:
         result = adapter.format_message("[click here](https://example.com)")
         assert result == "<https://example.com|click here>"
 
+    def test_link_conversion_strips_markdown_angle_brackets(self, adapter):
+        result = adapter.format_message("[click here](<https://example.com>)")
+        assert result == "<https://example.com|click here>"
+
+    def test_escapes_control_characters(self, adapter):
+        result = adapter.format_message("AT&T < 5 > 3")
+        assert result == "AT&amp;T &lt; 5 &gt; 3"
+
+    def test_preserves_existing_slack_entities(self, adapter):
+        text = "Hey <@U123>, see <https://example.com|example> and <!here>"
+        assert adapter.format_message(text) == text
+
     def test_strikethrough(self, adapter):
         assert adapter.format_message("~~deleted~~") == "~deleted~"
 
@@ -643,6 +655,325 @@ class TestFormatMessage:
     def test_none_passthrough(self, adapter):
         assert adapter.format_message(None) is None
 
+    def test_blockquote_preserved(self, adapter):
+        """Single-line blockquote > marker is preserved."""
+        assert adapter.format_message("> quoted text") == "> quoted text"
+
+    def test_multiline_blockquote(self, adapter):
+        """Multi-line blockquote preserves > on each line."""
+        text = "> line one\n> line two"
+        assert adapter.format_message(text) == "> line one\n> line two"
+
+    def test_blockquote_with_formatting(self, adapter):
+        """Blockquote containing bold text."""
+        assert adapter.format_message("> **bold quote**") == "> *bold quote*"
+
+    def test_nested_blockquote(self, adapter):
+        """Multiple > characters for nested quotes."""
+        assert adapter.format_message(">> deeply quoted") == ">> deeply quoted"
+
+    def test_blockquote_mixed_with_plain(self, adapter):
+        """Blockquote lines interleaved with plain text."""
+        text = "normal\n> quoted\nnormal again"
+        result = adapter.format_message(text)
+        assert "> quoted" in result
+        assert "normal" in result
+
+    def test_non_prefix_gt_still_escaped(self, adapter):
+        """Greater-than in mid-line is still escaped."""
+        assert adapter.format_message("5 > 3") == "5 &gt; 3"
+
+    def test_blockquote_with_code(self, adapter):
+        """Blockquote containing inline code."""
+        result = adapter.format_message("> use `fmt.Println`")
+        assert result.startswith(">")
+        assert "`fmt.Println`" in result
+
+    def test_bold_italic_combined(self, adapter):
+        """Triple-star ***text*** converts to Slack bold+italic *_text_*."""
+        assert adapter.format_message("***hello***") == "*_hello_*"
+
+    def test_bold_italic_with_surrounding_text(self, adapter):
+        """Bold+italic in a sentence."""
+        result = adapter.format_message("This is ***important*** stuff")
+        assert "*_important_*" in result
+
+    def test_bold_italic_does_not_break_plain_bold(self, adapter):
+        """**bold** still works after adding ***bold italic*** support."""
+        assert adapter.format_message("**bold**") == "*bold*"
+
+    def test_bold_italic_does_not_break_plain_italic(self, adapter):
+        """*italic* still works after adding ***bold italic*** support."""
+        assert adapter.format_message("*italic*") == "_italic_"
+
+    def test_bold_italic_mixed_with_bold(self, adapter):
+        """Both ***bold italic*** and **bold** in the same message."""
+        result = adapter.format_message("***important*** and **bold**")
+        assert "*_important_*" in result
+        assert "*bold*" in result
+
+    def test_pre_escaped_ampersand_not_double_escaped(self, adapter):
+        """Already-escaped &amp; must not become &amp;amp;."""
+        assert adapter.format_message("&amp;") == "&amp;"
+
+    def test_pre_escaped_lt_not_double_escaped(self, adapter):
+        """Already-escaped &lt; must not become &amp;lt;."""
+        assert adapter.format_message("&lt;") == "&lt;"
+
+    def test_pre_escaped_gt_not_double_escaped(self, adapter):
+        """Already-escaped &gt; in plain text must not become &amp;gt;."""
+        assert adapter.format_message("5 &gt; 3") == "5 &gt; 3"
+
+    def test_mixed_raw_and_escaped_entities(self, adapter):
+        """Raw & and pre-escaped &amp; coexist correctly."""
+        result = adapter.format_message("AT&T and &amp; entity")
+        assert result == "AT&amp;T and &amp; entity"
+
+    def test_link_with_parentheses_in_url(self, adapter):
+        """Wikipedia-style URL with balanced parens is not truncated."""
+        result = adapter.format_message("[Foo](https://en.wikipedia.org/wiki/Foo_(bar))")
+        assert result == "<https://en.wikipedia.org/wiki/Foo_(bar)|Foo>"
+
+    def test_link_with_multiple_paren_pairs(self, adapter):
+        """URL with multiple balanced paren pairs."""
+        result = adapter.format_message("[text](https://example.com/a_(b)_c_(d))")
+        assert result == "<https://example.com/a_(b)_c_(d)|text>"
+
+    def test_link_without_parens_still_works(self, adapter):
+        """Normal URL without parens is unaffected by regex change."""
+        result = adapter.format_message("[click](https://example.com/path?q=1)")
+        assert result == "<https://example.com/path?q=1|click>"
+
+    def test_link_with_angle_brackets_and_parens(self, adapter):
+        """Angle-bracket URL with parens (CommonMark syntax)."""
+        result = adapter.format_message("[Foo](<https://en.wikipedia.org/wiki/Foo_(bar)>)")
+        assert result == "<https://en.wikipedia.org/wiki/Foo_(bar)|Foo>"
+
+    def test_escaping_is_idempotent(self, adapter):
+        """Formatting already-formatted text produces the same result."""
+        original = "AT&T < 5 > 3"
+        once = adapter.format_message(original)
+        twice = adapter.format_message(once)
+        assert once == twice
+
+    # --- Entity preservation (spec-compliance) ---
+
+    def test_channel_mention_preserved(self, adapter):
+        """<!channel> special mention passes through unchanged."""
+        assert adapter.format_message("Attention <!channel>") == "Attention <!channel>"
+
+    def test_everyone_mention_preserved(self, adapter):
+        """<!everyone> special mention passes through unchanged."""
+        assert adapter.format_message("Hey <!everyone>") == "Hey <!everyone>"
+
+    def test_subteam_mention_preserved(self, adapter):
+        """<!subteam^ID> user group mention passes through unchanged."""
+        assert adapter.format_message("Paging <!subteam^S12345>") == "Paging <!subteam^S12345>"
+
+    def test_date_formatting_preserved(self, adapter):
+        """<!date^...> formatting token passes through unchanged."""
+        text = "Posted <!date^1392734382^{date_pretty}|Feb 18, 2014>"
+        assert adapter.format_message(text) == text
+
+    def test_channel_link_preserved(self, adapter):
+        """<#CHANNEL_ID> channel link passes through unchanged."""
+        assert adapter.format_message("Join <#C12345>") == "Join <#C12345>"
+
+    # --- Additional edge cases ---
+
+    def test_message_only_code_block(self, adapter):
+        """Entire message is a fenced code block — no conversion."""
+        code = "```python\nx = 1\n```"
+        assert adapter.format_message(code) == code
+
+    def test_multiline_mixed_formatting(self, adapter):
+        """Multi-line message with headers, bold, links, code, and blockquotes."""
+        text = "## Title\n**bold** and [link](https://x.com)\n> quote\n`code`"
+        result = adapter.format_message(text)
+        assert result.startswith("*Title*")
+        assert "*bold*" in result
+        assert "<https://x.com|link>" in result
+        assert "> quote" in result
+        assert "`code`" in result
+
+    def test_markdown_unordered_list_with_asterisk(self, adapter):
+        """Asterisk list items must not trigger italic conversion."""
+        text = "* item one\n* item two"
+        result = adapter.format_message(text)
+        assert "item one" in result
+        assert "item two" in result
+
+    def test_nested_bold_in_link(self, adapter):
+        """Bold inside link label — label is stashed before bold pass."""
+        result = adapter.format_message("[**bold**](https://example.com)")
+        assert "https://example.com" in result
+        assert "bold" in result
+
+    def test_url_with_query_string_and_ampersand(self, adapter):
+        """Ampersand in URL query string must not be escaped."""
+        result = adapter.format_message("[link](https://x.com?a=1&b=2)")
+        assert result == "<https://x.com?a=1&b=2|link>"
+
+    def test_emoji_shortcodes_passthrough(self, adapter):
+        """Emoji shortcodes like :smile: pass through unchanged."""
+        assert adapter.format_message(":smile: hello :wave:") == ":smile: hello :wave:"
+
+
+# ---------------------------------------------------------------------------
+# TestEditMessage
+# ---------------------------------------------------------------------------
+
+
+class TestEditMessage:
+    """Verify that edit_message() applies mrkdwn formatting before sending."""
+
+    @pytest.mark.asyncio
+    async def test_edit_message_formats_bold(self, adapter):
+        """edit_message converts **bold** to Slack *bold*."""
+        adapter._app.client.chat_update = AsyncMock(return_value={"ok": True})
+        await adapter.edit_message("C123", "1234.5678", "**hello world**")
+        kwargs = adapter._app.client.chat_update.call_args.kwargs
+        assert kwargs["text"] == "*hello world*"
+
+    @pytest.mark.asyncio
+    async def test_edit_message_formats_links(self, adapter):
+        """edit_message converts markdown links to Slack format."""
+        adapter._app.client.chat_update = AsyncMock(return_value={"ok": True})
+        await adapter.edit_message("C123", "1234.5678", "[click](https://example.com)")
+        kwargs = adapter._app.client.chat_update.call_args.kwargs
+        assert kwargs["text"] == "<https://example.com|click>"
+
+    @pytest.mark.asyncio
+    async def test_edit_message_preserves_blockquotes(self, adapter):
+        """edit_message preserves blockquote > markers."""
+        adapter._app.client.chat_update = AsyncMock(return_value={"ok": True})
+        await adapter.edit_message("C123", "1234.5678", "> quoted text")
+        kwargs = adapter._app.client.chat_update.call_args.kwargs
+        assert kwargs["text"] == "> quoted text"
+
+    @pytest.mark.asyncio
+    async def test_edit_message_escapes_control_chars(self, adapter):
+        """edit_message escapes & < > in plain text."""
+        adapter._app.client.chat_update = AsyncMock(return_value={"ok": True})
+        await adapter.edit_message("C123", "1234.5678", "AT&T < 5 > 3")
+        kwargs = adapter._app.client.chat_update.call_args.kwargs
+        assert kwargs["text"] == "AT&amp;T &lt; 5 &gt; 3"
+
+
+# ---------------------------------------------------------------------------
+# TestEditMessageStreamingPipeline
+# ---------------------------------------------------------------------------
+
+
+class TestEditMessageStreamingPipeline:
+    """E2E: verify that sequential streaming edits all go through format_message.
+
+    Simulates the GatewayStreamConsumer pattern where edit_message is called
+    repeatedly with progressively longer accumulated text.  Every call must
+    produce properly formatted mrkdwn in the chat_update payload.
+    """
+
+    @pytest.mark.asyncio
+    async def test_edit_message_formats_streaming_updates(self, adapter):
+        """Simulates streaming: multiple edits, each should be formatted."""
+        adapter._app.client.chat_update = AsyncMock(return_value={"ok": True})
+
+        # First streaming update — bold
+        result1 = await adapter.edit_message("C123", "ts1", "**Processing**...")
+        assert result1.success is True
+        kwargs1 = adapter._app.client.chat_update.call_args.kwargs
+        assert kwargs1["text"] == "*Processing*..."
+
+        # Second streaming update — bold + link
+        result2 = await adapter.edit_message(
+            "C123", "ts1", "**Done!** See [results](https://example.com)"
+        )
+        assert result2.success is True
+        kwargs2 = adapter._app.client.chat_update.call_args.kwargs
+        assert kwargs2["text"] == "*Done!* See <https://example.com|results>"
+
+    @pytest.mark.asyncio
+    async def test_edit_message_formats_code_and_bold(self, adapter):
+        """Streaming update with code block and bold — code must be preserved."""
+        adapter._app.client.chat_update = AsyncMock(return_value={"ok": True})
+
+        content = "**Result:**\n```python\nprint('hello')\n```"
+        result = await adapter.edit_message("C123", "ts1", content)
+        assert result.success is True
+        kwargs = adapter._app.client.chat_update.call_args.kwargs
+        assert kwargs["text"].startswith("*Result:*")
+        assert "```python\nprint('hello')\n```" in kwargs["text"]
+
+    @pytest.mark.asyncio
+    async def test_edit_message_formats_blockquote_in_stream(self, adapter):
+        """Streaming update with blockquote — '>' marker must survive."""
+        adapter._app.client.chat_update = AsyncMock(return_value={"ok": True})
+
+        content = "> **Important:** do this\nnormal line"
+        result = await adapter.edit_message("C123", "ts1", content)
+        assert result.success is True
+        kwargs = adapter._app.client.chat_update.call_args.kwargs
+        assert kwargs["text"].startswith("> *Important:*")
+        assert "normal line" in kwargs["text"]
+
+    @pytest.mark.asyncio
+    async def test_edit_message_formats_progressive_accumulation(self, adapter):
+        """Simulate real streaming: text grows with each edit, all formatted."""
+        adapter._app.client.chat_update = AsyncMock(return_value={"ok": True})
+
+        updates = [
+            ("**Step 1**", "*Step 1*"),
+            ("**Step 1**\n**Step 2**", "*Step 1*\n*Step 2*"),
+            (
+                "**Step 1**\n**Step 2**\nSee [docs](https://docs.example.com)",
+                "*Step 1*\n*Step 2*\nSee <https://docs.example.com|docs>",
+            ),
+        ]
+
+        for raw, expected in updates:
+            result = await adapter.edit_message("C123", "ts1", raw)
+            assert result.success is True
+            kwargs = adapter._app.client.chat_update.call_args.kwargs
+            assert kwargs["text"] == expected, f"Failed for input: {raw!r}"
+
+        # Total edit count should match number of updates
+        assert adapter._app.client.chat_update.call_count == len(updates)
+
+    @pytest.mark.asyncio
+    async def test_edit_message_formats_bold_italic(self, adapter):
+        """Bold+italic ***text*** is formatted as *_text_* in edited messages."""
+        adapter._app.client.chat_update = AsyncMock(return_value={"ok": True})
+        await adapter.edit_message("C123", "ts1", "***important*** update")
+        kwargs = adapter._app.client.chat_update.call_args.kwargs
+        assert "*_important_*" in kwargs["text"]
+
+    @pytest.mark.asyncio
+    async def test_edit_message_does_not_double_escape(self, adapter):
+        """Pre-escaped entities in edited messages must not get double-escaped."""
+        adapter._app.client.chat_update = AsyncMock(return_value={"ok": True})
+        await adapter.edit_message("C123", "ts1", "5 &gt; 3 and &amp; entity")
+        kwargs = adapter._app.client.chat_update.call_args.kwargs
+        assert "&amp;gt;" not in kwargs["text"]
+        assert "&amp;amp;" not in kwargs["text"]
+        assert "&gt;" in kwargs["text"]
+        assert "&amp;" in kwargs["text"]
+
+    @pytest.mark.asyncio
+    async def test_edit_message_formats_url_with_parens(self, adapter):
+        """Wikipedia-style URL with parens survives edit pipeline."""
+        adapter._app.client.chat_update = AsyncMock(return_value={"ok": True})
+        await adapter.edit_message("C123", "ts1", "See [Foo](https://en.wikipedia.org/wiki/Foo_(bar))")
+        kwargs = adapter._app.client.chat_update.call_args.kwargs
+        assert "<https://en.wikipedia.org/wiki/Foo_(bar)|Foo>" in kwargs["text"]
+
+    @pytest.mark.asyncio
+    async def test_edit_message_not_connected(self, adapter):
+        """edit_message returns failure when adapter is not connected."""
+        adapter._app = None
+        result = await adapter.edit_message("C123", "ts1", "**hello**")
+        assert result.success is False
+        assert "Not connected" in result.error
+
 
 # ---------------------------------------------------------------------------
 # TestReactions
@@ -1085,6 +1416,48 @@ class TestMessageSplitting:
         await adapter.send("C123", "hello world")
         assert adapter._app.client.chat_postMessage.call_count == 1
 
+    @pytest.mark.asyncio
+    async def test_send_preserves_blockquote_formatting(self, adapter):
+        """Blockquote '>' markers must survive format → chunk → send pipeline."""
+        adapter._app.client.chat_postMessage = AsyncMock(return_value={"ts": "ts1"})
+        await adapter.send("C123", "> quoted text\nnormal text")
+        kwargs = adapter._app.client.chat_postMessage.call_args.kwargs
+        sent_text = kwargs["text"]
+        assert sent_text.startswith("> quoted text")
+        assert "normal text" in sent_text
+
+    @pytest.mark.asyncio
+    async def test_send_formats_bold_italic(self, adapter):
+        """Bold+italic ***text*** is formatted as *_text_* in sent messages."""
+        adapter._app.client.chat_postMessage = AsyncMock(return_value={"ts": "ts1"})
+        await adapter.send("C123", "***important*** update")
+        kwargs = adapter._app.client.chat_postMessage.call_args.kwargs
+        assert "*_important_*" in kwargs["text"]
+
+    @pytest.mark.asyncio
+    async def test_send_explicitly_enables_mrkdwn(self, adapter):
+        adapter._app.client.chat_postMessage = AsyncMock(return_value={"ts": "ts1"})
+        await adapter.send("C123", "**hello**")
+        kwargs = adapter._app.client.chat_postMessage.call_args.kwargs
+        assert kwargs.get("mrkdwn") is True
+
+    @pytest.mark.asyncio
+    async def test_send_does_not_double_escape_entities(self, adapter):
+        """Pre-escaped &amp; in sent messages must not become &amp;amp;."""
+        adapter._app.client.chat_postMessage = AsyncMock(return_value={"ts": "ts1"})
+        await adapter.send("C123", "Use &amp; for ampersand")
+        kwargs = adapter._app.client.chat_postMessage.call_args.kwargs
+        assert "&amp;amp;" not in kwargs["text"]
+        assert "&amp;" in kwargs["text"]
+
+    @pytest.mark.asyncio
+    async def test_send_formats_url_with_parens(self, adapter):
+        """Wikipedia-style URL with parens survives send pipeline."""
+        adapter._app.client.chat_postMessage = AsyncMock(return_value={"ts": "ts1"})
+        await adapter.send("C123", "See [Foo](https://en.wikipedia.org/wiki/Foo_(bar))")
+        kwargs = adapter._app.client.chat_postMessage.call_args.kwargs
+        assert "<https://en.wikipedia.org/wiki/Foo_(bar)|Foo>" in kwargs["text"]
+
 
 # ---------------------------------------------------------------------------
 # TestReplyBroadcast

tests/tools/test_send_message_tool.py

@@ -32,6 +32,30 @@ def _install_telegram_mock(monkeypatch, bot):
     monkeypatch.setitem(sys.modules, "telegram.constants", constants_mod)
 
 
+def _ensure_slack_mock(monkeypatch):
+    if "slack_bolt" in sys.modules and hasattr(sys.modules["slack_bolt"], "__file__"):
+        return
+
+    slack_bolt = MagicMock()
+    slack_bolt.async_app.AsyncApp = MagicMock
+    slack_bolt.adapter.socket_mode.async_handler.AsyncSocketModeHandler = MagicMock
+
+    slack_sdk = MagicMock()
+    slack_sdk.web.async_client.AsyncWebClient = MagicMock
+
+    for name, mod in [
+        ("slack_bolt", slack_bolt),
+        ("slack_bolt.async_app", slack_bolt.async_app),
+        ("slack_bolt.adapter", slack_bolt.adapter),
+        ("slack_bolt.adapter.socket_mode", slack_bolt.adapter.socket_mode),
+        ("slack_bolt.adapter.socket_mode.async_handler", slack_bolt.adapter.socket_mode.async_handler),
+        ("slack_sdk", slack_sdk),
+        ("slack_sdk.web", slack_sdk.web),
+        ("slack_sdk.web.async_client", slack_sdk.web.async_client),
+    ]:
+        monkeypatch.setitem(sys.modules, name, mod)
+
+
 class TestSendMessageTool:
     def test_cron_duplicate_target_is_skipped_and_explained(self):
         home = SimpleNamespace(chat_id="-1001")
@@ -426,7 +450,7 @@ class TestSendToPlatformChunking:
             result = asyncio.run(
                 _send_to_platform(
                     Platform.DISCORD,
-                    SimpleNamespace(enabled=True, token="tok", extra={}),
+                    SimpleNamespace(enabled=True, token="***", extra={}),
                     "ch", long_msg,
                 )
             )
@@ -435,8 +459,115 @@ class TestSendToPlatformChunking:
         for call in send.await_args_list:
             assert len(call.args[2]) <= 2020  # each chunk fits the limit
 
+    def test_slack_messages_are_formatted_before_send(self, monkeypatch):
+        _ensure_slack_mock(monkeypatch)
+
+        import gateway.platforms.slack as slack_mod
+
+        monkeypatch.setattr(slack_mod, "SLACK_AVAILABLE", True)
+        send = AsyncMock(return_value={"success": True, "message_id": "1"})
+
+        with patch("tools.send_message_tool._send_slack", send):
+            result = asyncio.run(
+                _send_to_platform(
+                    Platform.SLACK,
+                    SimpleNamespace(enabled=True, token="***", extra={}),
+                    "C123",
+                    "**hello** from [Hermes](<https://example.com>)",
+                )
+            )
+
+        assert result["success"] is True
+        send.assert_awaited_once_with(
+            "***",
+            "C123",
+            "*hello* from <https://example.com|Hermes>",
+        )
+
+    def test_slack_bold_italic_formatted_before_send(self, monkeypatch):
+        """Bold+italic ***text*** survives tool-layer formatting."""
+        _ensure_slack_mock(monkeypatch)
+        import gateway.platforms.slack as slack_mod
+
+        monkeypatch.setattr(slack_mod, "SLACK_AVAILABLE", True)
+        send = AsyncMock(return_value={"success": True, "message_id": "1"})
+        with patch("tools.send_message_tool._send_slack", send):
+            result = asyncio.run(
+                _send_to_platform(
+                    Platform.SLACK,
+                    SimpleNamespace(enabled=True, token="***", extra={}),
+                    "C123",
+                    "***important*** update",
+                )
+            )
+        assert result["success"] is True
+        sent_text = send.await_args.args[2]
+        assert "*_important_*" in sent_text
+
+    def test_slack_blockquote_formatted_before_send(self, monkeypatch):
+        """Blockquote '>' markers must survive formatting (not escaped to '&gt;')."""
+        _ensure_slack_mock(monkeypatch)
+        import gateway.platforms.slack as slack_mod
+
+        monkeypatch.setattr(slack_mod, "SLACK_AVAILABLE", True)
+        send = AsyncMock(return_value={"success": True, "message_id": "1"})
+        with patch("tools.send_message_tool._send_slack", send):
+            result = asyncio.run(
+                _send_to_platform(
+                    Platform.SLACK,
+                    SimpleNamespace(enabled=True, token="***", extra={}),
+                    "C123",
+                    "> important quote\n\nnormal text & stuff",
+                )
+            )
+        assert result["success"] is True
+        sent_text = send.await_args.args[2]
+        assert sent_text.startswith("> important quote")
+        assert "&amp;" in sent_text  # & is escaped
+        assert "&gt;" not in sent_text.split("\n")[0]  # > in blockquote is NOT escaped
+
+    def test_slack_pre_escaped_entities_not_double_escaped(self, monkeypatch):
+        """Pre-escaped HTML entities survive tool-layer formatting without double-escaping."""
+        _ensure_slack_mock(monkeypatch)
+        import gateway.platforms.slack as slack_mod
+        monkeypatch.setattr(slack_mod, "SLACK_AVAILABLE", True)
+        send = AsyncMock(return_value={"success": True, "message_id": "1"})
+        with patch("tools.send_message_tool._send_slack", send):
+            result = asyncio.run(
+                _send_to_platform(
+                    Platform.SLACK,
+                    SimpleNamespace(enabled=True, token="***", extra={}),
+                    "C123",
+                    "AT&amp;T &lt;tag&gt; test",
+                )
+            )
+        assert result["success"] is True
+        sent_text = send.await_args.args[2]
+        assert "&amp;amp;" not in sent_text
+        assert "&amp;lt;" not in sent_text
+        assert "AT&amp;T" in sent_text
+
+    def test_slack_url_with_parens_formatted_before_send(self, monkeypatch):
+        """Wikipedia-style URL with parens survives tool-layer formatting."""
+        _ensure_slack_mock(monkeypatch)
+        import gateway.platforms.slack as slack_mod
+        monkeypatch.setattr(slack_mod, "SLACK_AVAILABLE", True)
+        send = AsyncMock(return_value={"success": True, "message_id": "1"})
+        with patch("tools.send_message_tool._send_slack", send):
+            result = asyncio.run(
+                _send_to_platform(
+                    Platform.SLACK,
+                    SimpleNamespace(enabled=True, token="***", extra={}),
+                    "C123",
+                    "See [Foo](https://en.wikipedia.org/wiki/Foo_(bar))",
+                )
+            )
+        assert result["success"] is True
+        sent_text = send.await_args.args[2]
+        assert "<https://en.wikipedia.org/wiki/Foo_(bar)|Foo>" in sent_text
+
     def test_telegram_media_attaches_to_last_chunk(self):
-        """When chunked, media files are sent only with the last chunk."""
+
         sent_calls = []
 
         async def fake_send(token, chat_id, message, media_files=None, thread_id=None):

tools/send_message_tool.py

@@ -322,6 +322,13 @@ async def _send_to_platform(platform, pconfig, chat_id, message, thread_id=None,
 
     media_files = media_files or []
 
+    if platform == Platform.SLACK and message:
+        try:
+            slack_adapter = SlackAdapter.__new__(SlackAdapter)
+            message = slack_adapter.format_message(message)
+        except Exception:
+            logger.debug("Failed to apply Slack mrkdwn formatting in _send_to_platform", exc_info=True)
+
     # Platform message length limits (from adapter class attributes)
     _MAX_LENGTHS = {
         Platform.TELEGRAM: TelegramAdapter.MAX_MESSAGE_LENGTH,
@@ -571,7 +578,8 @@ async def _send_slack(token, chat_id, message):
         url = "https://slack.com/api/chat.postMessage"
         headers = {"Authorization": f"Bearer {token}", "Content-Type": "application/json"}
         async with aiohttp.ClientSession(timeout=aiohttp.ClientTimeout(total=30)) as session:
-            async with session.post(url, headers=headers, json={"channel": chat_id, "text": message}) as resp:
+            payload = {"channel": chat_id, "text": message, "mrkdwn": True}
+            async with session.post(url, headers=headers, json=payload) as resp:
                 data = await resp.json()
                 if data.get("ok"):
                     return {"success": True, "platform": "slack", "chat_id": chat_id, "message_id": data.get("ts")}