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/runtime/__init__.py

@@ -0,0 +1,22 @@
+# 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.
+
+"""Artemis cross-platform runtime and process supervisor subsystem."""
+
+from artemis.runtime.supervisor import ProcessSupervisor, process_supervisor
+
+__all__ = [
+    "ProcessSupervisor",
+    "process_supervisor",
+]

artemis/runtime/supervisor.py

@@ -0,0 +1,94 @@
+# 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.
+
+"""Cross-platform Process Supervisor and Lifecycle Manager."""
+
+import asyncio
+from collections.abc import Sequence
+import os
+from pathlib import Path
+
+from artemis.platform import platform
+from artemis.utils.logger import get_logger
+
+logger = get_logger(__name__)
+
+
+class ProcessSupervisor:
+    """Manages process spawning, tree cleanup, signals, and UTF-8 stream handling."""
+
+    @staticmethod
+    def prepare_environment(extra_env: dict[str, str] | None = None) -> dict[str, str]:
+        """Prepare child process environment with guaranteed UTF-8 mode."""
+        env = os.environ.copy()
+        env["PYTHONUNBUFFERED"] = "1"
+        env["PYTHONUTF8"] = "1"
+        if extra_env:
+            env.update(extra_env)
+        return env
+
+    @staticmethod
+    async def spawn_async(
+        cmd: Sequence[str],
+        cwd: Path | str | None = None,
+        env: dict[str, str] | None = None,
+        capture_output: bool = True,
+    ) -> asyncio.subprocess.Process:
+        """Spawn an asynchronous subprocess with clean environment and cross-platform flags."""
+        prepared_env = ProcessSupervisor.prepare_environment(env)
+        cwd_str = str(cwd) if cwd else None
+
+        stdout_dest = asyncio.subprocess.PIPE if capture_output else None
+        stderr_dest = asyncio.subprocess.PIPE if capture_output else None
+
+        return await asyncio.create_subprocess_exec(
+            *cmd,
+            stdout=stdout_dest,
+            stderr=stderr_dest,
+            cwd=cwd_str,
+            env=prepared_env,
+        )
+
+    @staticmethod
+    def terminate_tree(pid: int, timeout_seconds: float = 3.0) -> bool:
+        """Recursively terminate a process tree."""
+        return platform.process.terminate_process_tree(pid, timeout_seconds=timeout_seconds)
+
+    @staticmethod
+    async def stop_process(
+        proc: asyncio.subprocess.Process | None,
+        timeout_seconds: float = 3.0,
+    ) -> None:
+        """Safely stop an asyncio Process and kill its children if necessary."""
+        if proc is None:
+            return
+
+        if proc.returncode is not None:
+            return
+
+        try:
+            if proc.pid:
+                ProcessSupervisor.terminate_tree(proc.pid, timeout_seconds=timeout_seconds)
+            else:
+                proc.terminate()
+            await asyncio.wait_for(proc.wait(), timeout=timeout_seconds)
+        except Exception as e:
+            logger.debug(f"Failed graceful stop for process {proc}: {e}")
+            try:
+                proc.kill()
+            except Exception:
+                pass
+
+
+process_supervisor: ProcessSupervisor = ProcessSupervisor()