fix(slack): truncate inflated original_text in approval/confirm chat.update handlers

Slack re-escapes HTML entities in the interaction payload
(< -> &lt;, > -> &gt;, & -> &amp;), inflating the section text
past the 3000-char Block Kit limit when the button handler
rebuilds updated_blocks for chat.update.

The send path already budget-truncates, but the click handlers
used the echoed original_text verbatim. Cap it to 3000 chars
in both _handle_approval_action and _handle_slash_confirm_action.

Fixes #53693

plugins/platforms/slack/adapter.py

@@ -4300,6 +4300,11 @@ class SlackAdapter(BasePlatformAdapter):
                 original_text = block.get("text", {}).get("text", "")
                 break
 
+        # Slack re-escapes HTML entities in the interaction payload
+        # (< → &lt;, > → &gt;, & → &amp;), which can inflate the text
+        # past the 3000-char section-block limit on chat.update.
+        original_text = original_text[:3000]
+
         updated_blocks = [
             {
                 "type": "section",
@@ -4467,6 +4472,11 @@ class SlackAdapter(BasePlatformAdapter):
                 original_text = block.get("text", {}).get("text", "")
                 break
 
+        # Slack re-escapes HTML entities in the interaction payload
+        # (< → &lt;, > → &gt;, & → &amp;), which can inflate the text
+        # past the 3000-char section-block limit on chat.update.
+        original_text = original_text[:3000]
+
         updated_blocks = [
             {
                 "type": "section",

tests/gateway/test_slack_approval_buttons.py

@@ -275,6 +275,37 @@ class TestSlackApprovalAction:
         update_kwargs = mock_client.chat_update.call_args[1]
         assert "Denied by alice" in update_kwargs["text"]
 
+    @pytest.mark.asyncio
+    async def test_truncates_inflated_original_text(self):
+        """Interaction payload re-escapes HTML entities; text must be capped."""
+        adapter = _make_adapter()
+        _attach_auth_runner(adapter)
+        adapter._approval_resolved["1.2"] = False
+
+        # Simulate Slack re-escaping: original was ~2990 chars, but & → &
+        # etc. inflates it past 3000.
+        inflated_text = "a" * 2990 + "&" * 10  # 2990 + 50 = 3040 chars
+
+        ack = AsyncMock()
+        body = {
+            "message": {"ts": "1.2", "blocks": [
+                {"type": "section", "text": {"type": "mrkdwn", "text": inflated_text}},
+            ]},
+            "channel": {"id": "C1"},
+            "user": {"name": "alice", "id": "U_ALICE"},
+        }
+        action = {"action_id": "hermes_approve_once", "value": "session-key"}
+
+        mock_client = adapter._team_clients["T1"]
+        mock_client.chat_update = AsyncMock()
+
+        with patch("tools.approval.resolve_gateway_approval", return_value=1):
+            await adapter._handle_approval_action(ack, body, action)
+
+        update_kwargs = mock_client.chat_update.call_args[1]
+        section_text = update_kwargs["blocks"][0]["text"]["text"]
+        assert len(section_text) <= 3000
+
     @pytest.mark.asyncio
     async def test_global_allowlist_blocks_unauthorized_click(self, monkeypatch):
         adapter = _make_adapter()
@@ -410,6 +441,40 @@ class TestSlackSlashConfirmAction:
         secondary_client.chat_postMessage.assert_awaited_once()
         adapter._team_clients["T1"].chat_update.assert_not_called()
 
+    @pytest.mark.asyncio
+    async def test_truncates_inflated_original_text(self):
+        """Interaction payload re-escapes HTML entities; text must be capped."""
+        adapter = _make_adapter()
+        _attach_auth_runner(adapter)
+        adapter._approval_resolved["2222.3333"] = False
+
+        # Simulate Slack re-escaping inflating text past 3000 chars.
+        inflated_text = "b" * 2990 + "&lt;" * 10  # 2990 + 40 = 3030 chars
+
+        ack = AsyncMock()
+        body = {
+            "message": {"ts": "2222.3333", "blocks": [
+                {"type": "section", "text": {"type": "mrkdwn", "text": inflated_text}},
+            ]},
+            "channel": {"id": "C1"},
+            "user": {"name": "owner", "id": "U_OWNER"},
+        }
+        action = {
+            "action_id": "hermes_confirm_once",
+            "value": "agent:main:slack:group:C1:1111|confirm-1",
+        }
+
+        mock_client = adapter._team_clients["T1"]
+        mock_client.chat_update = AsyncMock()
+        mock_client.chat_postMessage = AsyncMock()
+
+        with patch("tools.slash_confirm.resolve", new=AsyncMock(return_value="ok")):
+            await adapter._handle_slash_confirm_action(ack, body, action)
+
+        update_kwargs = mock_client.chat_update.call_args[1]
+        section_text = update_kwargs["blocks"][0]["text"]["text"]
+        assert len(section_text) <= 3000
+
 
 # ===========================================================================
 # _fetch_thread_context