fix: MCP toolset resolution for runtime and config (#3252)

Gateway sessions had their own inline toolset resolution that only read
platform_toolsets from config, which never includes MCP server names.
MCP tools were discovered and registered but invisible to the model.

- Replace duplicated gateway toolset resolution in _run_agent() and
  _run_background_task() with calls to the shared _get_platform_tools()
- Extend _get_platform_tools() to include globally enabled MCP servers
  at runtime (include_default_mcp_servers=True), while config-editing
  flows use include_default_mcp_servers=False to avoid persisting
  implicit MCP defaults into platform_toolsets
- Add homeassistant to PLATFORMS dict (was missing, caused KeyError)
- Fix CLI entry point to use _get_platform_tools() as well, so MCP
  tools are visible in CLI mode too
- Remove redundant platform_key reassignment in _run_background_task

Co-authored-by: kshitijk4poor <kshitijk4poor@users.noreply.github.com>

tests/gateway/test_reasoning_command.py

@@ -218,3 +218,112 @@ class TestReasoningCommand:
         assert result["final_response"] == "ok"
         assert _CapturingAgent.last_init is not None
         assert _CapturingAgent.last_init["reasoning_config"] == {"enabled": False}
+
+    def test_run_agent_includes_enabled_mcp_servers_in_gateway_toolsets(self, tmp_path, monkeypatch):
+        hermes_home = tmp_path / "hermes"
+        hermes_home.mkdir()
+        (hermes_home / "config.yaml").write_text(
+            "platform_toolsets:\n"
+            "  cli: [web, memory]\n"
+            "mcp_servers:\n"
+            "  exa:\n"
+            "    url: https://mcp.exa.ai/mcp\n"
+            "  web-search-prime:\n"
+            "    url: https://api.z.ai/api/mcp/web_search_prime/mcp\n",
+            encoding="utf-8",
+        )
+
+        monkeypatch.setattr(gateway_run, "_hermes_home", hermes_home)
+        monkeypatch.setattr(gateway_run, "_env_path", hermes_home / ".env")
+        monkeypatch.setattr(gateway_run, "load_dotenv", lambda *args, **kwargs: None)
+        monkeypatch.setattr(
+            gateway_run,
+            "_resolve_runtime_agent_kwargs",
+            lambda: {
+                "provider": "openrouter",
+                "api_mode": "chat_completions",
+                "base_url": "https://openrouter.ai/api/v1",
+                "api_key": "test-key",
+            },
+        )
+        fake_run_agent = types.ModuleType("run_agent")
+        fake_run_agent.AIAgent = _CapturingAgent
+        monkeypatch.setitem(sys.modules, "run_agent", fake_run_agent)
+
+        _CapturingAgent.last_init = None
+        runner = _make_runner()
+
+        source = SessionSource(
+            platform=Platform.LOCAL,
+            chat_id="cli",
+            chat_name="CLI",
+            chat_type="dm",
+            user_id="user-1",
+        )
+
+        result = asyncio.run(
+            runner._run_agent(
+                message="ping",
+                context_prompt="",
+                history=[],
+                source=source,
+                session_id="session-1",
+                session_key="agent:main:local:dm",
+            )
+        )
+
+        assert result["final_response"] == "ok"
+        assert _CapturingAgent.last_init is not None
+        enabled_toolsets = set(_CapturingAgent.last_init["enabled_toolsets"])
+        assert "web" in enabled_toolsets
+        assert "memory" in enabled_toolsets
+        assert "exa" in enabled_toolsets
+        assert "web-search-prime" in enabled_toolsets
+
+    def test_run_agent_homeassistant_uses_default_platform_toolset(self, tmp_path, monkeypatch):
+        hermes_home = tmp_path / "hermes"
+        hermes_home.mkdir()
+        (hermes_home / "config.yaml").write_text("", encoding="utf-8")
+
+        monkeypatch.setattr(gateway_run, "_hermes_home", hermes_home)
+        monkeypatch.setattr(gateway_run, "_env_path", hermes_home / ".env")
+        monkeypatch.setattr(gateway_run, "load_dotenv", lambda *args, **kwargs: None)
+        monkeypatch.setattr(
+            gateway_run,
+            "_resolve_runtime_agent_kwargs",
+            lambda: {
+                "provider": "openrouter",
+                "api_mode": "chat_completions",
+                "base_url": "https://openrouter.ai/api/v1",
+                "api_key": "test-key",
+            },
+        )
+        fake_run_agent = types.ModuleType("run_agent")
+        fake_run_agent.AIAgent = _CapturingAgent
+        monkeypatch.setitem(sys.modules, "run_agent", fake_run_agent)
+
+        _CapturingAgent.last_init = None
+        runner = _make_runner()
+
+        source = SessionSource(
+            platform=Platform.HOMEASSISTANT,
+            chat_id="ha",
+            chat_name="Home Assistant",
+            chat_type="dm",
+            user_id="user-1",
+        )
+
+        result = asyncio.run(
+            runner._run_agent(
+                message="ping",
+                context_prompt="",
+                history=[],
+                source=source,
+                session_id="session-1",
+                session_key="agent:main:homeassistant:dm",
+            )
+        )
+
+        assert result["final_response"] == "ok"
+        assert _CapturingAgent.last_init is not None
+        assert "homeassistant" in set(_CapturingAgent.last_init["enabled_toolsets"])