feat(slack): add gateway.slack.unfurl to suppress link previews

gateway/config.py

@@ -830,6 +830,8 @@ def load_gateway_config() -> GatewayConfig:
                     bridged["reply_in_thread"] = platform_cfg["reply_in_thread"]
                 if "require_mention" in platform_cfg:
                     bridged["require_mention"] = platform_cfg["require_mention"]
+                if plat == Platform.SLACK and "unfurl" in platform_cfg:
+                    bridged["unfurl"] = platform_cfg["unfurl"]
                 if plat == Platform.TELEGRAM and "allowed_chats" in platform_cfg:
                     bridged["allowed_chats"] = platform_cfg["allowed_chats"]
                 if plat == Platform.TELEGRAM and "group_allowed_chats" in platform_cfg:

gateway/platforms/slack.py

@@ -790,13 +790,20 @@ async def send(
             # reply_broadcast: also post thread replies to the main channel.
             # Controlled via platform config: gateway.slack.reply_broadcast
             broadcast = self.config.extra.get("reply_broadcast", False)
+            # When gateway.slack.unfurl is false, suppress Slack's link/media
+            # previews so posted URLs don't expand into preview cards. Defaults
+            # to true, preserving Slack's native unfurling behavior.
+            unfurl = self.config.extra.get("unfurl", True)
 
             for i, chunk in enumerate(chunks):
                 kwargs = {
                     "channel": chat_id,
                     "text": chunk,
                     "mrkdwn": True,
                 }
+                if not unfurl:
+                    kwargs["unfurl_links"] = False
+                    kwargs["unfurl_media"] = False
                 if thread_ts:
                     kwargs["thread_ts"] = thread_ts
                     # Only broadcast the first chunk of the first reply

tests/gateway/test_slack.py

@@ -15,7 +15,7 @@
 
 import pytest
 
-from gateway.config import Platform, PlatformConfig
+from gateway.config import Platform, PlatformConfig, load_gateway_config
 from gateway.platforms.base import (
     MessageEvent,
     MessageType,
@@ -2458,6 +2458,27 @@ async def test_send_explicitly_enables_mrkdwn(self, adapter):
         kwargs = adapter._app.client.chat_postMessage.call_args.kwargs
         assert kwargs.get("mrkdwn") is True
 
+    @pytest.mark.asyncio
+    async def test_send_disables_url_previews_when_unfurl_off(self, adapter):
+        """With gateway.slack.unfurl=false, posts must suppress link/media
+        unfurling so URLs don't expand into noisy preview cards."""
+        adapter.config.extra["unfurl"] = False
+        adapter._app.client.chat_postMessage = AsyncMock(return_value={"ts": "ts1"})
+        await adapter.send("C123", "see https://example.com/article")
+        kwargs = adapter._app.client.chat_postMessage.call_args.kwargs
+        assert kwargs.get("unfurl_links") is False
+        assert kwargs.get("unfurl_media") is False
+
+    @pytest.mark.asyncio
+    async def test_send_preserves_url_previews_by_default(self, adapter):
+        """Default behavior leaves Slack's unfurling untouched — no unfurl
+        flags are sent, so Slack applies its native preview behavior."""
+        adapter._app.client.chat_postMessage = AsyncMock(return_value={"ts": "ts1"})
+        await adapter.send("C123", "see https://example.com/article")
+        kwargs = adapter._app.client.chat_postMessage.call_args.kwargs
+        assert "unfurl_links" not in kwargs
+        assert "unfurl_media" not in kwargs
+
     @pytest.mark.asyncio
     async def test_send_does_not_double_escape_entities(self, adapter):
         """Pre-escaped & in sent messages must not become &."""
@@ -3177,3 +3198,27 @@ async def test_no_contextvar_does_not_match_any_context(self, adapter):
         # the normal single-user case; the ContextVar path is the precise one.
         # The key invariant is: when the ContextVar IS set, it matches exactly.
         assert ctx is not None  # fallback path finds the entry
+
+
+class TestUnfurlConfigBridging:
+    """gateway.slack.unfurl must bridge from YAML into PlatformConfig.extra so
+    the send path can read it — guards the allowlist wiring in
+    load_gateway_config (a non-allowlisted key would be silently dropped)."""
+
+    def _write_config(self, tmp_path, content: str):
+        hermes_home = tmp_path / ".hermes"
+        hermes_home.mkdir()
+        (hermes_home / "config.yaml").write_text(content, encoding="utf-8")
+        return hermes_home
+
+    def test_top_level_unfurl_false_bridges_to_extra(self, tmp_path, monkeypatch):
+        hermes_home = self._write_config(tmp_path, "slack:\n  unfurl: false\n")
+        monkeypatch.setenv("HERMES_HOME", str(hermes_home))
+        cfg = load_gateway_config()
+        assert cfg.platforms[Platform.SLACK].extra.get("unfurl") is False
+
+    def test_unfurl_absent_when_not_configured(self, tmp_path, monkeypatch):
+        hermes_home = self._write_config(tmp_path, "slack:\n  require_mention: true\n")
+        monkeypatch.setenv("HERMES_HOME", str(hermes_home))
+        cfg = load_gateway_config()
+        assert "unfurl" not in cfg.platforms[Platform.SLACK].extra

website/docs/user-guide/messaging/slack.md

@@ -343,6 +343,26 @@ platforms:
 | `platforms.slack.extra.reply_in_thread` | `true` | When `false`, channel messages get direct replies instead of threads. Messages inside existing threads still reply in-thread. |
 | `platforms.slack.extra.reply_broadcast` | `false` | When `true`, thread replies are also posted to the main channel. Only the first chunk is broadcast. |
 
+### Link Previews
+
+By default Slack expands posted URLs into preview cards ("unfurling"). For bots
+that post a lot of links — news feeds, digests, alerts — this is often noise.
+Set `unfurl: false` to suppress link and media previews on the bot's own posts:
+
+```yaml
+platforms:
+  slack:
+    extra:
+      # Suppress Slack link/media previews on the bot's posts (default: true)
+      unfurl: false
+```
+
+The top-level `slack.unfurl` shorthand is also accepted.
+
+| Key | Default | Description |
+|-----|---------|-------------|
+| `platforms.slack.extra.unfurl` | `true` | When `false`, the bot's posts disable Slack's `unfurl_links`/`unfurl_media`, so posted URLs don't expand into preview cards. |
+
 ### Session Isolation
 
 ```yaml