feat: add multi-device concurrency, server lifecycle CLI, and unified execution stream

- Implement DevicePool and DeviceExecutionLock concurrency modes (per-device FIFO vs global serialization)
- Extend ArtemisClient SDK and CLI with explicit device targeting and concurrency strategy configuration
- Add server lifecycle management (artemis restart, stop, status) with cross-platform PID discovery
- Update MCP server tools to support multi-device dispatch, trace tagging, and per-device execution
- Enhance Showcase UI with step-by-step visual replay, playback speed controls, and device serial badges
- Add comprehensive unit test coverage and edge-case verification scripts

mcp_server/tools/device_state.py

@@ -31,25 +31,37 @@ from artemis.utils.visualization import format_minimal_list_with_elements
 
 
 @mcp.tool()
-async def mobile_get_device_state(view_type: str) -> str:
+async def mobile_get_device_state(view_type: str, device_serial: str | None = None) -> str:
     """Real-time mobile device state observer (for debugging and validation).
 
     Use this tool to inspect the latest mobile status or to assist in tracking
     the subagent's task progress.
 
     Retrieves a real-time screenshot (returns local file URI) or a simplified
-    element tree text list of the currently connected mobile device.
+    element tree text list of the target mobile device.
+
+    ### Device Selection Modes:
+    1. **Direct Device Specification**: Provide `device_serial` to observe a specific
+       phone or emulator (e.g. `device_serial="63191FDKX00062"`).
+    2. **Automatic Device Selection**: Omit `device_serial` or leave it `None` to
+       automatically inspect the default/connected device.
+
+    **Diagnostics & User Preference**:
+    - When multiple devices are attached, prioritize letting the user specify or confirm the device.
+    - Run `adb devices` to check connected devices and identify their serial numbers.
 
     Args:
-        view_type: The observation type. Supported values: - "screenshot":
-          Captures the real-time mobile screen and saves it to the workspace,
-          returning the local URI path of the image file (e.g.,
-          "file:///path/to/screenshot.jpg"). - "hierarchy": Directly returns the
-          simplified text-labeled element list, which is identical to what the
-          mobile UI automation subagent sees when making decisions.
+        view_type: The observation type. Supported values:
+          - "screenshot": Captures the real-time mobile screen and saves it to the workspace,
+            returning the local URI path of the image file (e.g., "file:///path/to/screenshot.jpg").
+          - "hierarchy": Directly returns the simplified text-labeled element list, which is
+            identical to what the mobile UI automation subagent sees when making decisions.
+        device_serial: Optional Android device serial number (e.g., "63191FDKX00062" or
+          "emulator-5554"). If specified, inspects state from that specific device. If omitted,
+          inspects the default connected device.
     """
     try:
-        controller = _get_controller()
+        controller = _get_controller(device_serial=device_serial)
         device_width = controller.ctx.device.device_width
         device_height = controller.ctx.device.device_height
     except Exception as e: