feat: add SMS (Twilio) platform adapter

Add SMS as a first-class messaging platform via the Twilio API.
Shares credentials with the existing telephony skill — same
TWILIO_ACCOUNT_SID, TWILIO_AUTH_TOKEN, TWILIO_PHONE_NUMBER env vars.

Adapter (gateway/platforms/sms.py):
- aiohttp webhook server for inbound (Twilio form-encoded POSTs)
- Twilio REST API with Basic auth for outbound
- Markdown stripping, smart chunking at 1600 chars
- Echo loop prevention, phone number redaction in logs

Integration (13 files):
- gateway config, run, channel_directory
- agent prompt_builder (SMS platform hint)
- cron scheduler, cronjob tools
- send_message_tool (_send_sms via Twilio API)
- toolsets (hermes-sms + hermes-gateway)
- gateway setup wizard, status display
- pyproject.toml (sms optional extra)
- 21 tests

Docs:
- website/docs/user-guide/messaging/sms.md (full setup guide)
- Updated messaging index (architecture, toolsets, security, links)
- Updated environment-variables.md reference

Inspired by PR #1575 (@sunsakis), rewritten for Twilio.

tests/gateway/test_sms.py

@@ -0,0 +1,215 @@
+"""Tests for SMS (Twilio) platform integration.
+
+Covers config loading, format/truncate, echo prevention,
+requirements check, and toolset verification.
+"""
+
+import os
+from unittest.mock import patch
+
+import pytest
+
+from gateway.config import Platform, PlatformConfig, HomeChannel
+
+
+# ── Config loading ──────────────────────────────────────────────────
+
+class TestSmsConfigLoading:
+    """Verify _apply_env_overrides wires SMS correctly."""
+
+    def test_sms_platform_enum_exists(self):
+        assert Platform.SMS.value == "sms"
+
+    def test_env_overrides_create_sms_config(self):
+        from gateway.config import load_gateway_config
+
+        env = {
+            "TWILIO_ACCOUNT_SID": "ACtest123",
+            "TWILIO_AUTH_TOKEN": "token_abc",
+            "TWILIO_PHONE_NUMBER": "+15551234567",
+        }
+        with patch.dict(os.environ, env, clear=False):
+            config = load_gateway_config()
+            assert Platform.SMS in config.platforms
+            pc = config.platforms[Platform.SMS]
+            assert pc.enabled is True
+            assert pc.api_key == "token_abc"
+
+    def test_env_overrides_set_home_channel(self):
+        from gateway.config import load_gateway_config
+
+        env = {
+            "TWILIO_ACCOUNT_SID": "ACtest123",
+            "TWILIO_AUTH_TOKEN": "token_abc",
+            "TWILIO_PHONE_NUMBER": "+15551234567",
+            "SMS_HOME_CHANNEL": "+15559876543",
+            "SMS_HOME_CHANNEL_NAME": "My Phone",
+        }
+        with patch.dict(os.environ, env, clear=False):
+            config = load_gateway_config()
+            hc = config.platforms[Platform.SMS].home_channel
+            assert hc is not None
+            assert hc.chat_id == "+15559876543"
+            assert hc.name == "My Phone"
+            assert hc.platform == Platform.SMS
+
+    def test_sms_in_connected_platforms(self):
+        from gateway.config import load_gateway_config
+
+        env = {
+            "TWILIO_ACCOUNT_SID": "ACtest123",
+            "TWILIO_AUTH_TOKEN": "token_abc",
+        }
+        with patch.dict(os.environ, env, clear=False):
+            config = load_gateway_config()
+            connected = config.get_connected_platforms()
+            assert Platform.SMS in connected
+
+
+# ── Format / truncate ───────────────────────────────────────────────
+
+class TestSmsFormatAndTruncate:
+    """Test SmsAdapter.format_message strips markdown."""
+
+    def _make_adapter(self):
+        from gateway.platforms.sms import SmsAdapter
+
+        env = {
+            "TWILIO_ACCOUNT_SID": "ACtest",
+            "TWILIO_AUTH_TOKEN": "tok",
+            "TWILIO_PHONE_NUMBER": "+15550001111",
+        }
+        with patch.dict(os.environ, env):
+            pc = PlatformConfig(enabled=True, api_key="tok")
+            adapter = object.__new__(SmsAdapter)
+            adapter.config = pc
+            adapter._platform = Platform.SMS
+            adapter._account_sid = "ACtest"
+            adapter._auth_token = "tok"
+            adapter._from_number = "+15550001111"
+        return adapter
+
+    def test_strips_bold(self):
+        adapter = self._make_adapter()
+        assert adapter.format_message("**hello**") == "hello"
+
+    def test_strips_italic(self):
+        adapter = self._make_adapter()
+        assert adapter.format_message("*world*") == "world"
+
+    def test_strips_code_blocks(self):
+        adapter = self._make_adapter()
+        result = adapter.format_message("```python\nprint('hi')\n```")
+        assert "```" not in result
+        assert "print('hi')" in result
+
+    def test_strips_inline_code(self):
+        adapter = self._make_adapter()
+        assert adapter.format_message("`code`") == "code"
+
+    def test_strips_headers(self):
+        adapter = self._make_adapter()
+        assert adapter.format_message("## Title") == "Title"
+
+    def test_strips_links(self):
+        adapter = self._make_adapter()
+        assert adapter.format_message("[click](https://example.com)") == "click"
+
+    def test_collapses_newlines(self):
+        adapter = self._make_adapter()
+        result = adapter.format_message("a\n\n\n\nb")
+        assert result == "a\n\nb"
+
+
+# ── Echo prevention ────────────────────────────────────────────────
+
+class TestSmsEchoPrevention:
+    """Adapter should ignore messages from its own number."""
+
+    def test_own_number_detection(self):
+        """The adapter stores _from_number for echo prevention."""
+        from gateway.platforms.sms import SmsAdapter
+
+        env = {
+            "TWILIO_ACCOUNT_SID": "ACtest",
+            "TWILIO_AUTH_TOKEN": "tok",
+            "TWILIO_PHONE_NUMBER": "+15550001111",
+        }
+        with patch.dict(os.environ, env):
+            pc = PlatformConfig(enabled=True, api_key="tok")
+            adapter = SmsAdapter(pc)
+            assert adapter._from_number == "+15550001111"
+
+
+# ── Requirements check ─────────────────────────────────────────────
+
+class TestSmsRequirements:
+    def test_check_sms_requirements_missing_sid(self):
+        from gateway.platforms.sms import check_sms_requirements
+
+        env = {"TWILIO_AUTH_TOKEN": "tok"}
+        with patch.dict(os.environ, env, clear=True):
+            assert check_sms_requirements() is False
+
+    def test_check_sms_requirements_missing_token(self):
+        from gateway.platforms.sms import check_sms_requirements
+
+        env = {"TWILIO_ACCOUNT_SID": "ACtest"}
+        with patch.dict(os.environ, env, clear=True):
+            assert check_sms_requirements() is False
+
+    def test_check_sms_requirements_both_set(self):
+        from gateway.platforms.sms import check_sms_requirements
+
+        env = {
+            "TWILIO_ACCOUNT_SID": "ACtest",
+            "TWILIO_AUTH_TOKEN": "tok",
+        }
+        with patch.dict(os.environ, env, clear=False):
+            # Only returns True if aiohttp is also importable
+            result = check_sms_requirements()
+            try:
+                import aiohttp  # noqa: F401
+                assert result is True
+            except ImportError:
+                assert result is False
+
+
+# ── Toolset verification ───────────────────────────────────────────
+
+class TestSmsToolset:
+    def test_hermes_sms_toolset_exists(self):
+        from toolsets import get_toolset
+
+        ts = get_toolset("hermes-sms")
+        assert ts is not None
+        assert "tools" in ts
+
+    def test_hermes_sms_in_gateway_includes(self):
+        from toolsets import get_toolset
+
+        gw = get_toolset("hermes-gateway")
+        assert gw is not None
+        assert "hermes-sms" in gw["includes"]
+
+    def test_sms_platform_hint_exists(self):
+        from agent.prompt_builder import PLATFORM_HINTS
+
+        assert "sms" in PLATFORM_HINTS
+        assert "concise" in PLATFORM_HINTS["sms"].lower()
+
+    def test_sms_in_scheduler_platform_map(self):
+        """Verify cron scheduler recognizes 'sms' as a valid platform."""
+        # Just check the Platform enum has SMS — the scheduler imports it dynamically
+        assert Platform.SMS.value == "sms"
+
+    def test_sms_in_send_message_platform_map(self):
+        """Verify send_message_tool recognizes 'sms'."""
+        # The platform_map is built inside _handle_send; verify SMS enum exists
+        assert hasattr(Platform, "SMS")
+
+    def test_sms_in_cronjob_deliver_description(self):
+        """Verify cronjob_tools mentions sms in deliver description."""
+        from tools.cronjob_tools import CRONJOB_SCHEMA
+        deliver_desc = CRONJOB_SCHEMA["parameters"]["properties"]["deliver"]["description"]
+        assert "sms" in deliver_desc.lower()