fix(simplex): use structured /_send for standalone DM text sends

The _standalone_send() function (used by the send_message tool for
proactive/scheduled sends) has the same bare `@<id> text` bug that
send() had before PR #44444. SimpleX's `@<x>` syntax resolves x as a
display name, not a contactId — the daemon silently drops messages
when it cannot find a contact named "6".

Use the structured `/_send @<id> json [...]` form, matching what
send_image, send_document, and the send() fix already use.

Fixes #46265

plugins/platforms/simplex/adapter.py

@@ -1269,8 +1269,10 @@ async def _standalone_send(
             )
             cmd_str = f"/_send #{group_id} json {composed}"
         else:
-            # Direct contacts are addressed by display name without brackets.
-            cmd_str = f"@{chat_id} {message}"
+            composed = json.dumps(
+                [{"msgContent": {"type": "text", "text": message}}]
+            )
+            cmd_str = f"/_send @{chat_id} json {composed}"
 
         payload = {
             "corrId": f"{_CORR_PREFIX}snd-{int(time.time() * 1000)}",

tests/gateway/test_simplex_plugin.py

@@ -298,6 +298,64 @@ async def test_standalone_send_missing_websockets(monkeypatch):
             sys.modules["websockets"] = saved_websockets
 
 
+@pytest.mark.asyncio
+async def test_standalone_send_defaults_to_local_daemon(monkeypatch):
+    monkeypatch.delenv("SIMPLEX_WS_URL", raising=False)
+    pconfig = MagicMock()
+    pconfig.extra = {}
+
+    sent_payloads = []
+
+    class DummyWs:
+        async def __aenter__(self):
+            return self
+
+        async def __aexit__(self, exc_type, exc, tb):
+            return None
+
+        async def send(self, payload):
+            sent_payloads.append(json.loads(payload))
+
+    def fake_connect(url, **kwargs):
+        assert url == "ws://127.0.0.1:5225"
+        assert kwargs["open_timeout"] == 10
+        assert kwargs["close_timeout"] == 5
+        return DummyWs()
+
+    import websockets
+    monkeypatch.setattr(websockets, "connect", fake_connect)
+
+    result = await _standalone_send(pconfig, "contact-42", "hi")
+    assert result == {"success": True, "platform": "simplex", "chat_id": "contact-42"}
+    assert sent_payloads[0]["cmd"].startswith("/_send @contact-42 json ")
+    msg_content = json.loads(
+        sent_payloads[0]["cmd"].split(" json ", 1)[1]
+    )[0]["msgContent"]
+    assert msg_content == {"type": "text", "text": "hi"}
+
+
+@pytest.mark.asyncio
+async def test_health_monitor_does_not_reconnect_quiet_healthy_ws(monkeypatch):
+    from gateway.config import PlatformConfig
+    cfg = PlatformConfig(enabled=True, extra={"ws_url": "ws://localhost:5225"})
+    adapter = SimplexAdapter(cfg)
+    adapter._running = True
+    adapter._last_ws_activity = 0
+    adapter._ws = AsyncMock()
+
+    monkeypatch.setattr(_simplex, "HEALTH_CHECK_INTERVAL", 0.01)
+    monkeypatch.setattr(_simplex, "HEALTH_CHECK_STALE_THRESHOLD", 0.01)
+
+    task = asyncio.create_task(adapter._health_monitor())
+    await asyncio.sleep(0.03)
+    adapter._running = False
+    await asyncio.wait_for(task, timeout=1)
+
+    adapter._ws.close.assert_not_called()
+
+
+
+
 # ---------------------------------------------------------------------------
 # 10. register() — plugin-side metadata
 # ---------------------------------------------------------------------------