feat: extract in-process MCP action layer, concurrent task dispatch, and spawn/reconcile hardening

- Extract device action execution into artemis/mcp action layer:
  typed ActionResult, capability manifest with startup validation,
  AdbActuator as the single physical implementation, in-memory
  ActionSession (replaces stdio subprocess MCP in validator), and
  McpActionExecutor preserving the legacy executor contract.
  adb_server keeps its external stdio/SSE surface unchanged and now
  reuses the actuator implementation; import-time side effects moved
  into configure_stdio_mode().
- Capability-gated prompt assembly (prompt_assembly.py): tool enums and
  teaching segments render per available backend tools; full-set output
  is byte-identical to the previous static text (locked by tests).
- Admin console task queue: serial worker replaced by a per-device
  concurrent dispatcher (ARTEMIS_CONCURRENCY_MODE=global restores
  serial semantics), per-session cancellation, strict device binding on
  enqueue, unified stdio piping with tee to trace stdout.log, and
  shutdown cleanup of all active runs. Fix _pid_exists exception order
  so PermissionError is treated as alive.
- mcp_server reliability: spawn watchdog kills runners stuck before
  interpreter startup and releases device reservations; task state
  reconcile uses psutil liveness, prefers runner-reported pids, and
  adds a 45s startup grace to stop false failure reports on Windows;
  conversation_id is now optional end-to-end; explicit device_serial is
  validated at submission.
- CLI install now writes ~/.claude/rules/artemis.md for Claude Code and
  migrates/removes the legacy CLAUDE.md injection block; ~/.claude.json
  is never rewritten when it fails to parse.
- Tests: Windows-portable stdio lifecycle and path assertions; new
  suites for action layer, prompt assembly, spawn watchdog, and task
  reconcile (895 passed, 3 skipped).

artemis/context.py

@@ -176,11 +176,26 @@ class ArtemisContext(BaseModel):
     _mobile_controller: Any | None = PrivateAttr(default=None)
     mcp_client_ctx: Any | None = None
     mcp_session: Any | None = None
+    action_session: Any | None = None
+    """In-process unified action MCP session (artemis.mcp.action_session)."""
+    actuator: Any | None = None
+    """Optional actuator backend override (artemis.mcp.actuators). ``None`` selects
+    the default AdbActuator; installing e.g. a robot-arm backend happens here."""
 
     async def __aenter__(self) -> ArtemisContext:
         return self
 
     async def __aexit__(self, exc_type, exc_val, exc_tb):
+        # Close the in-process action session before draining background tasks so its
+        # owner task exits cleanly rather than being cancelled below.
+        if self.action_session is not None:
+            try:
+                await self.action_session.aclose()
+            except Exception:
+                pass
+            finally:
+                self.action_session = None
+
         if self.background_tasks:
             tasks = list(self.background_tasks)
             pending_tasks = [task for task in tasks if not task.done()]