fix(slack): preserve thread-parent context when cron/bot posted the parent

The Slack thread-context fetcher used to drop every message with a
bot_id, which silently erased the thread parent whenever a cron job (or
any other bot) had posted it. As a result, replies to a cron-posted
summary lost all context and the agent answered as if from a blank
thread.

Changes:

1. gateway/platforms/slack.py::_fetch_thread_context
   - Keep the thread parent even when it was posted by a bot
     (e.g. cron summaries, third-party integrations).
   - Only skip *our own* prior bot replies to avoid circular context,
     matching the per-workspace bot user id via _team_bot_user_ids so
     multi-workspace deployments stay correct.
   - Keep non-self bot children (useful third-party context).

2. gateway/platforms/slack.py::_handle_slack_message
   - Populate MessageEvent.reply_to_text for thread replies (parity
     with Telegram/Discord/Feishu/WeCom). gateway.run uses this field
     to inject a [Replying to: "..."] prefix when the parent is not
     already in the session history, which is exactly the scenario
     triggered by cron-generated thread parents.
   - New helper _fetch_thread_parent_text reuses the existing thread-
     context cache (and its 60s TTL) to avoid duplicate
     conversations.replies calls; falls back to a cheap limit=1 fetch
     when the cache is cold.

Tests:

- Updated TestSlackThreadContext::test_skips_bot_messages to reflect
  the new behaviour (self-bot child dropped, third-party bot kept).
- Added:
    * test_fetch_thread_context_includes_bot_parent
    * test_fetch_thread_context_excludes_self_bot_replies
    * test_fetch_thread_context_multi_workspace
    * test_fetch_thread_context_current_ts_excluded (regression guard)
    * test_fetch_thread_parent_text_from_cache
    * test_slack_reply_to_text_set_on_thread_reply
    * test_slack_reply_to_text_none_for_top_level_message

Full Slack suite: 176 passed (was 169).

gateway/platforms/slack.py

@@ -55,6 +55,7 @@ class _ThreadContextCache:
     content: str
     fetched_at: float = field(default_factory=time.monotonic)
     message_count: int = 0
+    parent_text: str = ""  # Raw text of the thread parent (for reply_to_text injection)
 
 
 def check_slack_requirements() -> bool:
@@ -1291,6 +1292,22 @@ class SlackAdapter(BasePlatformAdapter):
             self.config.extra, channel_id, None,
         )
 
+        # Extract reply context if this message is a thread reply.
+        # Mirrors the Telegram/Discord implementations so that gateway.run
+        # can inject a `[Replying to: "..."]` prefix when the parent is not
+        # already in the session history. Uses the thread-context cache when
+        # available to avoid redundant conversations.replies calls.
+        reply_to_text = None
+        if thread_ts and thread_ts != ts:
+            try:
+                reply_to_text = await self._fetch_thread_parent_text(
+                    channel_id=channel_id,
+                    thread_ts=thread_ts,
+                    team_id=team_id,
+                ) or None
+            except Exception:  # pragma: no cover - defensive
+                reply_to_text = None
+
         msg_event = MessageEvent(
             text=text,
             message_type=msg_type,
@@ -1301,6 +1318,7 @@ class SlackAdapter(BasePlatformAdapter):
             media_types=media_types,
             reply_to_message_id=thread_ts if thread_ts != ts else None,
             channel_prompt=_channel_prompt,
+            reply_to_text=reply_to_text,
         )
 
         # Only react when bot is directly addressed (DM or @mention).
@@ -1555,14 +1573,37 @@ class SlackAdapter(BasePlatformAdapter):
 
             bot_uid = self._team_bot_user_ids.get(team_id, self._bot_user_id)
             context_parts = []
+            parent_text = ""
             for msg in messages:
                 msg_ts = msg.get("ts", "")
                 # Exclude the current triggering message — it will be delivered
                 # as the user message itself, so including it here would duplicate it.
                 if msg_ts == current_ts:
                     continue
-                # Exclude our own bot messages to avoid circular context.
+
-                if msg.get("bot_id") or msg.get("subtype") == "bot_message":
+                is_parent = msg_ts == thread_ts
+                is_bot = bool(msg.get("bot_id")) or msg.get("subtype") == "bot_message"
+                msg_user = msg.get("user", "")
+
+                # Identify "our own" bot for this workspace (multi-workspace safe).
+                msg_team = msg.get("team") or team_id
+                self_bot_uid = (
+                    self._team_bot_user_ids.get(msg_team)
+                    if msg_team
+                    else None
+                ) or self._bot_user_id
+
+                # Exclude only our own prior bot replies (circular context).
+                # Keep:
+                #   - the thread parent even if it was posted by a bot
+                #     (e.g. a cron job summary we are now replying to);
+                #   - other bots' child messages (useful third-party context).
+                if (
+                    is_bot
+                    and not is_parent
+                    and self_bot_uid
+                    and msg_user == self_bot_uid
+                ):
                     continue
 
                 msg_text = msg.get("text", "").strip()
@@ -1573,11 +1614,15 @@ class SlackAdapter(BasePlatformAdapter):
                 if bot_uid:
                     msg_text = msg_text.replace(f"<@{bot_uid}>", "").strip()
 
-                msg_user = msg.get("user", "unknown")
-                is_parent = msg_ts == thread_ts
                 prefix = "[thread parent] " if is_parent else ""
-                name = await self._resolve_user_name(msg_user, chat_id=channel_id)
+                display_user = msg_user or "unknown"
+                # Prefer the bot's own name when the message is a bot post.
+                if is_bot and not display_user:
+                    display_user = msg.get("username") or "bot"
+                name = await self._resolve_user_name(display_user, chat_id=channel_id)
                 context_parts.append(f"{prefix}{name}: {msg_text}")
+                if is_parent:
+                    parent_text = msg_text
 
             content = ""
             if context_parts:
@@ -1591,6 +1636,7 @@ class SlackAdapter(BasePlatformAdapter):
                 content=content,
                 fetched_at=now,
                 message_count=len(context_parts),
+                parent_text=parent_text,
             )
             return content
 
@@ -1598,6 +1644,47 @@ class SlackAdapter(BasePlatformAdapter):
             logger.warning("[Slack] Failed to fetch thread context: %s", e)
             return ""
 
+    async def _fetch_thread_parent_text(
+        self, channel_id: str, thread_ts: str, team_id: str = "",
+    ) -> str:
+        """Return the raw text of the thread parent message (for reply_to_text).
+
+        Uses the same per-thread cache as :meth:`_fetch_thread_context` to avoid
+        hitting ``conversations.replies`` twice. Falls back to a cheap single-
+        message fetch (``limit=1, inclusive=True``) when the cache is cold.
+
+        Returns empty string on any failure — callers should treat an empty
+        return as "no parent context to inject".
+        """
+        cache_key = f"{channel_id}:{thread_ts}"
+        now = time.monotonic()
+        cached = self._thread_context_cache.get(cache_key)
+        if cached and (now - cached.fetched_at) < self._THREAD_CACHE_TTL:
+            return cached.parent_text
+
+        try:
+            client = self._get_client(channel_id)
+            result = await client.conversations_replies(
+                channel=channel_id,
+                ts=thread_ts,
+                limit=1,
+                inclusive=True,
+            )
+            messages = result.get("messages", []) if result else []
+            if not messages:
+                return ""
+            parent = messages[0]
+            if parent.get("ts", "") != thread_ts:
+                return ""
+            bot_uid = self._team_bot_user_ids.get(team_id, self._bot_user_id)
+            text = (parent.get("text") or "").strip()
+            if bot_uid:
+                text = text.replace(f"<@{bot_uid}>", "").strip()
+            return text
+        except Exception as exc:  # pragma: no cover - defensive
+            logger.debug("[Slack] Failed to fetch thread parent text: %s", exc)
+            return ""
+
     async def _handle_slash_command(self, command: dict) -> None:
         """Handle Slack slash commands.
 

tests/gateway/test_slack.py

@@ -2011,3 +2011,76 @@ class TestProgressMessageThread:
             "so each @mention starts its own thread"
         )
         assert msg_event.message_id == "2000000000.000001"
+
+
+class TestSlackReplyToText:
+    """Ensure MessageEvent.reply_to_text is populated on thread replies so
+    gateway.run can inject a ``[Replying to: "..."]`` prefix (parity with
+    Telegram/Discord/Feishu/WeCom)."""
+
+    @pytest.mark.asyncio
+    async def test_slack_reply_to_text_set_on_thread_reply(self, adapter):
+        """When a thread reply arrives and the parent was posted by a bot
+        (e.g. cron summary), reply_to_text must carry the parent's text."""
+        adapter._channel_team = {}  # primary workspace only
+        adapter._team_bot_user_ids = {}
+
+        # Mock conversations_replies to return a bot-posted parent
+        adapter._app.client.conversations_replies = AsyncMock(return_value={
+            "messages": [
+                {
+                    "ts": "1000.0",
+                    "bot_id": "B_CRON",
+                    "text": "メール要約: 新着メール3件あります",
+                },
+                {"ts": "1000.5", "user": "U_USER", "text": "詳細を教えて"},
+            ]
+        })
+
+        # Use a DM so mention-gating doesn't short-circuit the handler.
+        event = {
+            "text": "詳細を教えて",
+            "user": "U_USER",
+            "channel": "D123",
+            "channel_type": "im",
+            "ts": "1000.5",
+            "thread_ts": "1000.0",  # thread reply
+        }
+
+        with patch.object(
+            adapter, "_resolve_user_name", new=AsyncMock(return_value="Alice")
+        ):
+            await adapter._handle_slack_message(event)
+
+        assert adapter.handle_message.call_args is not None, (
+            "handle_message must be invoked for thread-reply DM"
+        )
+        msg_event = adapter.handle_message.call_args[0][0]
+        assert msg_event.reply_to_message_id == "1000.0"
+        # The critical assertion: parent text is exposed as reply_to_text so the
+        # gateway can inject it when not already in the session history.
+        assert msg_event.reply_to_text is not None
+        assert "メール要約" in msg_event.reply_to_text
+
+    @pytest.mark.asyncio
+    async def test_slack_reply_to_text_none_for_top_level_message(self, adapter):
+        """Top-level messages (no thread_ts) must not set reply_to_text."""
+        event = {
+            "text": "hello",
+            "user": "U_USER",
+            "channel": "D123",
+            "channel_type": "im",
+            "ts": "1000.0",
+            # no thread_ts — top-level DM
+        }
+
+        with patch.object(
+            adapter, "_resolve_user_name", new=AsyncMock(return_value="Alice")
+        ):
+            await adapter._handle_slack_message(event)
+
+        assert adapter.handle_message.call_args is not None
+        msg_event = adapter.handle_message.call_args[0][0]
+        assert msg_event.reply_to_text is None
+        # Top-level message: reply_to_message_id must be falsy (None or empty).
+        assert not msg_event.reply_to_message_id

tests/gateway/test_slack_approval_buttons.py

@@ -276,23 +276,44 @@ class TestSlackThreadContext:
 
     @pytest.mark.asyncio
     async def test_skips_bot_messages(self):
+        """Self-bot child replies are skipped to avoid circular context,
+        but non-self bots (e.g. cron posts, third-party integrations) are kept.
+
+        Regression guard for the fix in _fetch_thread_context: previously ALL
+        bot messages were dropped, which lost context when the bot was replying
+        to a cron-posted thread parent."""
         adapter = _make_adapter()
         mock_client = adapter._team_clients["T1"]
         mock_client.conversations_replies = AsyncMock(return_value={
             "messages": [
                 {"ts": "1000.0", "user": "U1", "text": "Parent"},
-                {"ts": "1000.1", "bot_id": "B1", "text": "Bot reply (should be skipped)"},
+                # Self-bot reply -> must be skipped (circular)
+                {
+                    "ts": "1000.1",
+                    "bot_id": "B_SELF",
+                    "user": "U_BOT",
+                    "text": "Previous bot self-reply (should be skipped)",
+                },
+                # Third-party bot child -> kept (useful context)
+                {
+                    "ts": "1000.15",
+                    "bot_id": "B_OTHER",
+                    "user": "U_OTHER_BOT",
+                    "text": "Deploy succeeded",
+                },
                 {"ts": "1000.2", "user": "U1", "text": "Current"},
             ]
         })
-        adapter._user_name_cache = {"U1": "Alice"}
+        adapter._user_name_cache = {"U1": "Alice", "U_OTHER_BOT": "DeployBot"}
 
         context = await adapter._fetch_thread_context(
             channel_id="C1", thread_ts="1000.0", current_ts="1000.2", team_id="T1"
         )
 
-        assert "Bot reply" not in context
+        assert "Previous bot self-reply" not in context
         assert "Alice: Parent" in context
+        # Third-party bot message must now be included
+        assert "Deploy succeeded" in context
 
     @pytest.mark.asyncio
     async def test_empty_thread(self):
@@ -316,6 +337,166 @@ class TestSlackThreadContext:
         )
         assert context == ""
 
+    @pytest.mark.asyncio
+    async def test_fetch_thread_context_includes_bot_parent(self):
+        """The thread parent posted by a bot (e.g. a cron summary) must be
+        included in the context, prefixed with ``[thread parent]``."""
+        adapter = _make_adapter()
+        mock_client = adapter._team_clients["T1"]
+        mock_client.conversations_replies = AsyncMock(return_value={
+            "messages": [
+                # Bot-posted parent (cron job)
+                {
+                    "ts": "1000.0",
+                    "bot_id": "B123",
+                    "subtype": "bot_message",
+                    "username": "cron",
+                    "text": "メール要約: 本日の新着3件",
+                },
+                # User reply that triggered the fetch
+                {"ts": "1000.1", "user": "U1", "text": "詳細を教えて"},
+            ]
+        })
+        adapter._user_name_cache = {"U1": "Alice"}
+
+        context = await adapter._fetch_thread_context(
+            channel_id="C1",
+            thread_ts="1000.0",
+            current_ts="1000.1",  # exclude the trigger message itself
+            team_id="T1",
+        )
+
+        assert "[thread parent]" in context
+        assert "メール要約: 本日の新着3件" in context
+
+    @pytest.mark.asyncio
+    async def test_fetch_thread_context_excludes_self_bot_replies(self):
+        """Parent (non-self bot) is kept, self-bot child replies are dropped,
+        user replies are kept."""
+        adapter = _make_adapter()
+        mock_client = adapter._team_clients["T1"]
+        mock_client.conversations_replies = AsyncMock(return_value={
+            "messages": [
+                {"ts": "1000.0", "bot_id": "B_CRON", "text": "Cron summary"},
+                # Self-bot child reply -> excluded
+                {
+                    "ts": "1000.1",
+                    "bot_id": "B_SELF",
+                    "user": "U_BOT",  # matches adapter._bot_user_id
+                    "text": "Previous self reply",
+                },
+                # User reply -> kept
+                {"ts": "1000.2", "user": "U1", "text": "Follow-up question"},
+                # Current trigger (excluded by current_ts match)
+                {"ts": "1000.3", "user": "U1", "text": "Current"},
+            ]
+        })
+        adapter._user_name_cache = {"U1": "Alice"}
+
+        context = await adapter._fetch_thread_context(
+            channel_id="C1", thread_ts="1000.0", current_ts="1000.3", team_id="T1"
+        )
+
+        assert "Cron summary" in context
+        assert "[thread parent]" in context
+        assert "Previous self reply" not in context
+        assert "Follow-up question" in context
+        assert "Current" not in context
+
+    @pytest.mark.asyncio
+    async def test_fetch_thread_context_multi_workspace(self):
+        """Self-bot filtering must use the per-workspace bot user id so a
+        self-bot id that belongs to a different workspace does not accidentally
+        filter out a legitimate message in the current workspace."""
+        adapter = _make_adapter()
+        # Add a second workspace with a different bot user id
+        adapter._team_clients["T2"] = AsyncMock()
+        adapter._team_bot_user_ids = {"T1": "U_BOT_T1", "T2": "U_BOT_T2"}
+        adapter._bot_user_id = "U_BOT_T1"
+        adapter._channel_team["C2"] = "T2"
+
+        mock_client = adapter._team_clients["T2"]
+        mock_client.conversations_replies = AsyncMock(return_value={
+            "messages": [
+                {"ts": "2000.0", "user": "U2", "text": "Parent T2"},
+                # This has the *T1* bot's user id — from T2's perspective this
+                # is a third-party bot, so it must be kept.
+                {
+                    "ts": "2000.1",
+                    "bot_id": "B_FOREIGN",
+                    "user": "U_BOT_T1",
+                    "team": "T2",
+                    "text": "Cross-workspace bot reply",
+                },
+                # Self-bot for T2 — must be skipped
+                {
+                    "ts": "2000.2",
+                    "bot_id": "B_SELF_T2",
+                    "user": "U_BOT_T2",
+                    "team": "T2",
+                    "text": "Own T2 bot reply",
+                },
+                {"ts": "2000.3", "user": "U2", "text": "Current"},
+            ]
+        })
+        adapter._user_name_cache = {"U2": "Bob"}
+
+        context = await adapter._fetch_thread_context(
+            channel_id="C2", thread_ts="2000.0", current_ts="2000.3", team_id="T2"
+        )
+
+        assert "Parent T2" in context
+        assert "Cross-workspace bot reply" in context
+        assert "Own T2 bot reply" not in context
+
+    @pytest.mark.asyncio
+    async def test_fetch_thread_context_current_ts_excluded(self):
+        """Regression guard: the message whose ts == current_ts must never
+        appear in the context output (it will be delivered as the user
+        message itself)."""
+        adapter = _make_adapter()
+        mock_client = adapter._team_clients["T1"]
+        mock_client.conversations_replies = AsyncMock(return_value={
+            "messages": [
+                {"ts": "1000.0", "user": "U1", "text": "Parent"},
+                {"ts": "1000.1", "user": "U1", "text": "DO NOT INCLUDE THIS"},
+            ]
+        })
+        adapter._user_name_cache = {"U1": "Alice"}
+
+        context = await adapter._fetch_thread_context(
+            channel_id="C1", thread_ts="1000.0", current_ts="1000.1", team_id="T1"
+        )
+
+        assert "Parent" in context
+        assert "DO NOT INCLUDE THIS" not in context
+
+    @pytest.mark.asyncio
+    async def test_fetch_thread_parent_text_from_cache(self):
+        """_fetch_thread_parent_text should reuse the thread-context cache
+        when it is warm, avoiding an extra conversations.replies call."""
+        adapter = _make_adapter()
+        mock_client = adapter._team_clients["T1"]
+        mock_client.conversations_replies = AsyncMock(return_value={
+            "messages": [
+                {"ts": "1000.0", "bot_id": "B123", "text": "Parent summary"},
+                {"ts": "1000.1", "user": "U1", "text": "reply"},
+            ]
+        })
+
+        # Warm the cache via _fetch_thread_context
+        await adapter._fetch_thread_context(
+            channel_id="C1", thread_ts="1000.0", current_ts="1000.1", team_id="T1"
+        )
+        assert mock_client.conversations_replies.await_count == 1
+
+        parent = await adapter._fetch_thread_parent_text(
+            channel_id="C1", thread_ts="1000.0", team_id="T1"
+        )
+        assert parent == "Parent summary"
+        # No additional API call
+        assert mock_client.conversations_replies.await_count == 1
+
 
 # ===========================================================================
 # _has_active_session_for_thread — session key fix (#5833)