feat: introduce MCP server, cross-platform runtime, and Showcase UI reorganization

- Showcase UI Reorganization:
  * Move web UI dashboard from root directory into apps/showcase_ui/ for cleaner project structure
  * Add 'artemis ui' CLI command (artemis/interfaces/cli/commands/ui.py) and launcher scripts for the interactive showcase console
- Standalone MCP Server & Notifiers (mcp_server/):
  * Implement dedicated MCP server package with mobile automation tools (device_state, inspect_trace, task_manager, task_runner)
  * Add multi-channel notifiers (AgentAPI, Desktop notifications, Webhooks, File output, and Composite routing)
  * Introduce background task runner and trace store for autonomous mobile execution monitoring
- Cross-Platform Runtime & Toolchain Support:
  * Add artemis/platform/ with OS-specific implementations for Linux, macOS (Darwin), and Windows
  * Add artemis/runtime/supervisor.py for resilient process and agent runtime supervision
  * Add artemis/toolchain/ with dependency resolution and SDK descriptors
  * Add cross-platform launcher scripts (start.sh, start.bat) and installer scripts (scripts/install_deps.*)
- Core Enhancements & Diagnostics:
  * Enhance coordinate normalization, OCR API fallback, and perception pipeline
  * Add credential validation (credentials_validator.py) and system diagnostics
  * Update bilingual documentation (README.md, README_CN.md) and architecture diagrams
- Test Suite Expansion:
  * Add integration tests for cloud gateway, remote ADB, and Artemis login
  * Add unit tests covering core diagnostics, platform detection, toolchain, credentials validator, optional OCR, and MCP tools

artemis/platform/darwin.py

@@ -0,0 +1,150 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""macOS Platform Implementation (Apple Filesystem Hierarchy & Homebrew Integration)."""
+
+import os
+from pathlib import Path
+import shutil
+import signal
+import tempfile
+
+from artemis.platform.base import IPlatform, IPlatformPaths, IPlatformProcess, OSType
+
+
+class DarwinPlatformPaths(IPlatformPaths):
+    """macOS paths adhering to Apple standard Library/Application Support structure."""
+
+    def __init__(self):
+        self._home = Path.home()
+
+    @property
+    def config_dir(self) -> Path:
+        p = self._home / "Library" / "Application Support" / "artemis"
+        p.mkdir(parents=True, exist_ok=True)
+        return p
+
+    @property
+    def data_dir(self) -> Path:
+        env_dir = os.getenv("ARTEMIS_APP_DIR") or os.getenv("ANTIGRAVITY_APP_DIR")
+        if env_dir:
+            p = Path(env_dir)
+            p.mkdir(parents=True, exist_ok=True)
+            return p
+
+        # Check legacy ~/.artemis or ~/.gemini/jetski directory if it exists
+        legacy_artemis = self._home / ".artemis"
+        if legacy_artemis.exists():
+            return legacy_artemis
+
+        legacy_jetski = self._home / ".gemini" / "jetski"
+        if legacy_jetski.exists():
+            return legacy_jetski
+
+        p = self._home / "Library" / "Application Support" / "artemis"
+        p.mkdir(parents=True, exist_ok=True)
+        return p
+
+    @property
+    def cache_dir(self) -> Path:
+        p = self._home / "Library" / "Caches" / "artemis"
+        p.mkdir(parents=True, exist_ok=True)
+        return p
+
+    @property
+    def logs_dir(self) -> Path:
+        p = self._home / "Library" / "Logs" / "artemis"
+        p.mkdir(parents=True, exist_ok=True)
+        return p
+
+    def temp_dir(self, subfolder: str | None = None) -> Path:
+        base = Path(tempfile.gettempdir()) / "artemis"
+        target = base / subfolder if subfolder else base
+        target.mkdir(parents=True, exist_ok=True)
+        return target
+
+    def resolve_app_dir(self) -> Path:
+        return self.data_dir
+
+
+class DarwinPlatformProcess(IPlatformProcess):
+    """macOS process management."""
+
+    @property
+    def path_separator(self) -> str:
+        return ":"
+
+    def terminate_process_tree(self, pid: int, timeout_seconds: float = 3.0) -> bool:
+        try:
+            import psutil
+
+            parent = psutil.Process(pid)
+            children = parent.children(recursive=True)
+            for child in children:
+                try:
+                    child.send_signal(signal.SIGTERM)
+                except (psutil.NoSuchProcess, psutil.AccessDenied):
+                    pass
+
+            parent.send_signal(signal.SIGTERM)
+            gone, alive = psutil.wait_procs(children + [parent], timeout=timeout_seconds)
+            for p in alive:
+                try:
+                    p.kill()
+                except (psutil.NoSuchProcess, psutil.AccessDenied):
+                    pass
+            return True
+        except Exception:
+            try:
+                os.kill(pid, signal.SIGKILL)
+                return True
+            except OSError:
+                return False
+
+    def setup_utf8_io(self) -> None:
+        pass
+
+
+class DarwinPlatform(IPlatform):
+    """macOS Platform Adapter."""
+
+    def __init__(self):
+        self._paths = DarwinPlatformPaths()
+        self._process = DarwinPlatformProcess()
+
+    @property
+    def os_type(self) -> OSType:
+        return OSType.MACOS
+
+    @property
+    def paths(self) -> IPlatformPaths:
+        return self._paths
+
+    @property
+    def process(self) -> IPlatformProcess:
+        return self._process
+
+    def get_package_manager_name(self) -> str | None:
+        if shutil.which("brew"):
+            return "brew"
+        return None
+
+    def get_install_command(self, tool_name: str) -> str:
+        pkg_map = {
+            "adb": "android-platform-tools",
+            "ffmpeg": "ffmpeg",
+            "scrcpy": "scrcpy",
+        }
+        pkg = pkg_map.get(tool_name, tool_name)
+        return f"brew install {pkg}"