refactor(queue): split task queue orchestration and worker I/O

apps/admin_console/services/task_queue_service.py

@@ -13,13 +13,10 @@
 # limitations under the License.
 
 import asyncio
-import codecs
 from datetime import datetime
 import logging
 import os
-import psutil
 import shutil
-import subprocess
 import sys
 import time
 from typing import Any
@@ -28,10 +25,12 @@ import uuid
 try:
     from admin_console.core.state import state
     from admin_console.database.repositories.session_repository import session_repo
+    from admin_console.services import worker_process_io
     from admin_console.services.media_service import media_service
 except ImportError:
     from apps.admin_console.core.state import state
     from apps.admin_console.database.repositories.session_repository import session_repo
+    from apps.admin_console.services import worker_process_io
     from apps.admin_console.services.media_service import media_service
 
 from artemis.config import (
@@ -154,101 +153,12 @@ class TaskQueueService:
             return normalized, False
         return ("completed" if returncode == 0 else "failed"), True
 
-    @staticmethod
-    def _subprocess_creation_kwargs() -> dict[str, Any]:
-        """Isolate task workers from the UI server's Windows console.
-
-        A new process group alone is insufficient on Windows: the worker still
-        shares the parent's console, so a CTRL_C_EVENT generated anywhere in
-        that console can reach the UI server. CREATE_NO_WINDOW removes that
-        shared console boundary.
-
-        Output is captured on every platform so it can be forwarded to the
-        server terminal and teed into the trace's stdout.log (the daemon itself
-        is often spawned with its stdio discarded, so inheriting would lose the
-        worker's logs entirely).
-        """
-        kwargs: dict[str, Any] = {
-            "stdout": asyncio.subprocess.PIPE,
-            "stderr": asyncio.subprocess.STDOUT,
-        }
-        if sys.platform == "win32":
-            kwargs["creationflags"] = (
-                subprocess.CREATE_NEW_PROCESS_GROUP | subprocess.CREATE_NO_WINDOW
-            )
-        return kwargs
-
-    @staticmethod
-    async def _forward_worker_output(
-        stream: asyncio.StreamReader | None, log_path: str | None = None
-    ) -> None:
-        """Forward a worker's combined output without corrupting UTF-8.
-
-        When ``log_path`` is given, the output is also teed into that file so
-        the trace's advertised stdout.log actually exists for diagnostics.
-        """
-        if stream is None:
-            return
-
-        log_file = None
-        if log_path:
-            try:
-                os.makedirs(os.path.dirname(log_path), exist_ok=True)
-                log_file = open(log_path, "w", buffering=1, encoding="utf-8", errors="replace")
-            except Exception as exc:
-                print(f"[QueueWorker] Could not open worker log file '{log_path}': {exc}")
-
-        def _emit(text: str) -> None:
-            sys.stdout.write(text)
-            sys.stdout.flush()
-            if log_file is not None:
-                try:
-                    log_file.write(text)
-                except (OSError, ValueError):
-                    # Best-effort tee into stdout.log; console output above
-                    # already carried the text.
-                    pass
-
-        try:
-            decoder = codecs.getincrementaldecoder("utf-8")(errors="replace")
-            while True:
-                chunk = await stream.read(4096)
-                if not chunk:
-                    break
-                text = decoder.decode(chunk)
-                if text:
-                    _emit(text)
-
-            tail = decoder.decode(b"", final=True)
-            if tail:
-                _emit(tail)
-        finally:
-            if log_file is not None:
-                try:
-                    log_file.close()
-                except OSError:
-                    # Flush-on-close of the best-effort tee failed; nothing to do.
-                    pass
-
-    @staticmethod
-    async def _finish_output_forwarder(output_task: asyncio.Task[None] | None) -> None:
-        """Drain final worker output without allowing inherited handles to stall the queue."""
-        if output_task is None:
-            return
-        try:
-            await asyncio.wait_for(asyncio.shield(output_task), timeout=2.0)
-        except asyncio.CancelledError:
-            if output_task.cancelled():
-                return
-            raise
-        except TimeoutError:
-            output_task.cancel()
-            try:
-                await output_task
-            except asyncio.CancelledError:
-                pass
-        except Exception as exc:
-            print(f"[QueueWorker] Failed to forward detached worker output: {exc}")
+    # Worker subprocess I/O plumbing lives in worker_process_io; the historical
+    # private names stay bound here so callers and tests keep working unchanged.
+    _subprocess_creation_kwargs = staticmethod(worker_process_io.subprocess_creation_kwargs)
+    _forward_worker_output = staticmethod(worker_process_io.forward_worker_output)
+    _finish_output_forwarder = staticmethod(worker_process_io.finish_output_forwarder)
+    _wait_for_worker_process = staticmethod(worker_process_io.wait_for_worker_process)
 
     @staticmethod
     async def _terminate_worker_process(proc: asyncio.subprocess.Process | None) -> None:
@@ -263,27 +173,6 @@ class TaskQueueService:
         except ProcessLookupError:
             pass
 
-    @staticmethod
-    async def _wait_for_worker_process(proc: asyncio.subprocess.Process) -> int:
-        """Wait for worker process to exit, with watchdog fallback if PID was reaped externally."""
-        while True:
-            try:
-                return await asyncio.wait_for(proc.wait(), timeout=1.0)
-            except TimeoutError:
-                pid = getattr(proc, "pid", None)
-                if pid:
-                    try:
-                        p = psutil.Process(pid)
-                        if not p.is_running() or p.status() == psutil.STATUS_ZOMBIE:
-                            return proc.returncode if proc.returncode is not None else -15
-                    except (psutil.NoSuchProcess, ProcessLookupError):
-                        return proc.returncode if proc.returncode is not None else -15
-                    except psutil.Error:
-                        # Transient probe failure (e.g. AccessDenied): keep waiting.
-                        pass
-                else:
-                    return proc.returncode if proc.returncode is not None else -15
-
     @classmethod
     def ensure_worker_running(cls):
         """Guarantees that the background queue worker task is active and running."""
@@ -414,21 +303,15 @@ class TaskQueueService:
                 break
 
     @classmethod
-    async def _execute_task_item(cls, task_item: dict[str, Any]) -> None:
-        """Run one queued task to completion in its own worker subprocess."""
-        sess_id = task_item.get("session_id")
-        run_key = str(sess_id) if sess_id else uuid.uuid4().hex
-        goal = task_item.get("goal")
-        profile = task_item.get("profile", "flash")
-        proc: asyncio.subprocess.Process | None = None
-        output_task: asyncio.Task[None] | None = None
-        try:
-            if not isinstance(goal, str) or not goal.strip():
-                raise ValueError("Queued task must contain a non-empty string goal.")
-            expected_output = task_item.get("expected_output")
-            enable_outputter = task_item.get("enable_outputter")
-            locked_app = task_item.get("locked_app_package") or task_item.get("locked_app")
-            app_path = task_item.get("app_path")
+    def _begin_task_run(
+        cls,
+        task_item: dict[str, Any],
+        run_key: str,
+        sess_id: Any,
+        goal: str,
+        profile: str,
+    ) -> None:
+        """Mark the task as running and announce the launch to subscribers."""
         task_item["status"] = "running"
         task_item["start_time"] = time.time()
 
@@ -457,6 +340,22 @@ class TaskQueueService:
             },
         )
 
+    @classmethod
+    def _build_worker_invocation(
+        cls,
+        task_item: dict[str, Any],
+        run_key: str,
+        sess_id: Any,
+        goal: str,
+        profile: str,
+        target: AdbTarget,
+    ) -> tuple[list[str], dict[str, str]]:
+        """Assemble the worker subprocess command line and environment."""
+        expected_output = task_item.get("expected_output")
+        enable_outputter = task_item.get("enable_outputter")
+        locked_app = task_item.get("locked_app_package") or task_item.get("locked_app")
+        app_path = task_item.get("app_path")
+
         test_name = f"web_{int(time.time())}_{run_key[:8]}"
         env = os.environ.copy()
         pythonpath_parts = [
@@ -474,7 +373,6 @@ class TaskQueueService:
             env["ARTEMIS_SESSION_ID"] = str(sess_id)
         env["ARTEMIS_TASK_INGRESS"] = str(task_item.get("ingress", "frontend"))
         env["ARTEMIS_TASK_WORKER"] = "1"
-            target = cls._task_target(task_item)
         target.endpoint.apply_to_environment(env)
         env[DeviceExecutionLock.LOCK_SCOPE_ENV] = target.lock_scope
         queue_ticket = task_item.get("queue_ticket")
@@ -505,16 +403,21 @@ class TaskQueueService:
         if device_serial:
             cmd.extend(["--device-serial", str(device_serial)])
             env["ADB_DEVICE_SERIAL"] = str(device_serial)
+        return cmd, env
 
-            print(
-                f"[QueueWorker] Starting task [{sess_id}]: '{goal}' (profile: {profile}, device: {device_serial or 'auto'}, outputter: {bool(expected_output or enable_outputter)})"
-            )
-            proc = await asyncio.create_subprocess_exec(
-                *cmd,
-                cwd=str(WORKSPACE_ROOT),
-                env=env,
-                **cls._subprocess_creation_kwargs(),
-            )
+    @classmethod
+    def _register_worker_run(
+        cls,
+        task_item: dict[str, Any],
+        run_key: str,
+        sess_id: Any,
+        goal: str,
+        profile: str,
+        target: AdbTarget,
+        proc: asyncio.subprocess.Process,
+    ) -> None:
+        """Record the spawned worker in shared state and hand it the device reservation."""
+        device_serial = task_item.get("device_serial")
         state.current_process = proc
         task_item["pid"] = proc.pid
         state.active_runs[run_key] = {
@@ -541,7 +444,7 @@ class TaskQueueService:
         )
         ingress_type = str(task_item.get("ingress", "frontend"))
         DeviceExecutionLock.transfer_reservation(
-                str(queue_ticket),
+            str(task_item.get("queue_ticket")),
             proc.pid,
             description=f"{ingress_type} task: {goal[:120]}",
             device_id=device_serial or "pending",
@@ -549,6 +452,12 @@ class TaskQueueService:
             ingress=ingress_type,
             lock_scope=target.lock_scope,
         )
+
+    @classmethod
+    def _start_output_forwarder(
+        cls, sess_id: Any, proc: asyncio.subprocess.Process
+    ) -> asyncio.Task[None] | None:
+        """Start forwarding the worker's output; returns the forwarder task, if any."""
         # Forward the worker's combined output and tee it into the trace's
         # stdout.log so the log paths advertised by the MCP API exist.
         log_path = None
@@ -558,10 +467,16 @@ class TaskQueueService:
             except Exception:
                 log_path = None
         if isinstance(proc.stdout, asyncio.StreamReader):
-                output_task = asyncio.create_task(
+            return asyncio.create_task(
                 cls._forward_worker_output(proc.stdout, log_path)
             )
+        return None
 
+    @classmethod
+    async def _terminate_if_cancelled_during_launch(
+        cls, run_key: str, sess_id: Any, proc: asyncio.subprocess.Process
+    ) -> None:
+        """Terminate a worker whose task was cancelled while it was being launched."""
         if sess_id and (
             str(sess_id) in getattr(state, "cancelled_session_ids", set())
             or run_key in state.manually_stopped_run_ids
@@ -571,16 +486,11 @@ class TaskQueueService:
             )
             await cls._terminate_worker_process(proc)
 
-            # 3. Await subprocess completion
-            returncode = await cls._wait_for_worker_process(proc)
-            print(f"[QueueWorker] Task [{sess_id}] exited with returncode {returncode}")
-
-            manual_stop = run_key in state.manually_stopped_run_ids or bool(
-                sess_id and str(sess_id) in state.cancelled_session_ids
-            )
-
-            # 4. Perform fallback database status update and notification
-            if sess_id:
+    @classmethod
+    async def _persist_terminal_session_status(
+        cls, sess_id: Any, returncode: int, manual_stop: bool
+    ) -> str:
+        """Resolve and persist the session's terminal status in the DB and trace store."""
         current_status = session_repo.get_session_status(sess_id)
         new_status, should_persist = cls._resolve_terminal_status(
             current_status,
@@ -628,6 +538,11 @@ class TaskQueueService:
                     attempt + 1,
                     exc,
                 )
+        return new_status
+
+    @classmethod
+    async def _recover_or_fail_recording(cls, sess_id: Any) -> None:
+        """Attempt recovery of a not-yet-ready recording, else mark it failed."""
         rec_info = session_repo.get_video_recording_for_session(sess_id)
         rec_status = (rec_info or {}).get("status")
         recovered_video_path = None
@@ -659,6 +574,16 @@ class TaskQueueService:
                     {"session_id": sess_id, "error": recording_error},
                 )
 
+    @classmethod
+    def _announce_session_end(
+        cls,
+        task_item: dict[str, Any],
+        sess_id: Any,
+        goal: str,
+        new_status: str,
+        manual_stop: bool,
+    ) -> None:
+        """Broadcast session_ended and dispatch the external completion notification."""
         state.active_connections.pop(sess_id, None)
         cls._broadcast_event(
             "session_ended",
@@ -689,16 +614,11 @@ class TaskQueueService:
             except Exception as notif_err:
                 print(f"[QueueWorker] Notification dispatch notice: {notif_err}")
 
-        except asyncio.CancelledError:
-            print(f"[QueueWorker] Task [{sess_id}] received cancellation signal.")
-            if proc is not None and proc.returncode is None:
-                await cls._terminate_worker_process(proc)
-            raise
-        except Exception as e:
-            print(f"[QueueWorker] Unexpected error executing task [{sess_id}]: {e}")
-        finally:
-            await cls._finish_output_forwarder(output_task)
-            # 5. Clean up the finished task and release this run's scheduling slot
+    @classmethod
+    def _release_run_slot(
+        cls, sess_id: Any, run_key: str, proc: asyncio.subprocess.Process | None
+    ) -> None:
+        """Clean up the finished task and release this run's scheduling slot."""
         if sess_id:
             cls._remove_task(sess_id)
             state.cancelled_session_ids.discard(str(sess_id))
@@ -717,26 +637,80 @@ class TaskQueueService:
         state.wake_event.set()
 
     @classmethod
-    async def enqueue_tasks(
+    async def _execute_task_item(cls, task_item: dict[str, Any]) -> None:
+        """Run one queued task to completion in its own worker subprocess."""
+        sess_id = task_item.get("session_id")
+        run_key = str(sess_id) if sess_id else uuid.uuid4().hex
+        goal = task_item.get("goal")
+        profile = task_item.get("profile", "flash")
+        proc: asyncio.subprocess.Process | None = None
+        output_task: asyncio.Task[None] | None = None
+        try:
+            if not isinstance(goal, str) or not goal.strip():
+                raise ValueError("Queued task must contain a non-empty string goal.")
+            cls._begin_task_run(task_item, run_key, sess_id, goal, profile)
+
+            target = cls._task_target(task_item)
+            cmd, env = cls._build_worker_invocation(
+                task_item, run_key, sess_id, goal, profile, target
+            )
+
+            device_serial = task_item.get("device_serial")
+            print(
+                f"[QueueWorker] Starting task [{sess_id}]: '{goal}' (profile: {profile}, device: {device_serial or 'auto'}, outputter: {bool(task_item.get('expected_output') or task_item.get('enable_outputter'))})"
+            )
+            proc = await asyncio.create_subprocess_exec(
+                *cmd,
+                cwd=str(WORKSPACE_ROOT),
+                env=env,
+                **cls._subprocess_creation_kwargs(),
+            )
+            cls._register_worker_run(
+                task_item, run_key, sess_id, goal, profile, target, proc
+            )
+            output_task = cls._start_output_forwarder(sess_id, proc)
+            await cls._terminate_if_cancelled_during_launch(run_key, sess_id, proc)
+
+            # 3. Await subprocess completion
+            returncode = await cls._wait_for_worker_process(proc)
+            print(f"[QueueWorker] Task [{sess_id}] exited with returncode {returncode}")
+
+            manual_stop = run_key in state.manually_stopped_run_ids or bool(
+                sess_id and str(sess_id) in state.cancelled_session_ids
+            )
+
+            # 4. Perform fallback database status update and notification
+            if sess_id:
+                new_status = await cls._persist_terminal_session_status(
+                    sess_id, returncode, manual_stop
+                )
+                await cls._recover_or_fail_recording(sess_id)
+                cls._announce_session_end(
+                    task_item, sess_id, goal, new_status, manual_stop
+                )
+
+        except asyncio.CancelledError:
+            print(f"[QueueWorker] Task [{sess_id}] received cancellation signal.")
+            if proc is not None and proc.returncode is None:
+                await cls._terminate_worker_process(proc)
+            raise
+        except Exception as e:
+            print(f"[QueueWorker] Unexpected error executing task [{sess_id}]: {e}")
+        finally:
+            await cls._finish_output_forwarder(output_task)
+            # 5. Clean up the finished task and release this run's scheduling slot
+            cls._release_run_slot(sess_id, run_key, proc)
+
+    @classmethod
+    def _find_duplicate_submission(
         cls,
         goals: list[str],
-        profile: str = "flash",
-        expected_output: str | None = None,
-        enable_outputter: bool | None = None,
-        locked_app_package: str | None = None,
-        app_path: str | None = None,
-        device_serial: str | None = None,
-        ingress: str = "frontend",
-        session_id: str | None = None,
-        conversation_id: str | None = None,
-    ) -> dict[str, Any]:
-        """Enqueues one or more goals and wakes up the background worker."""
-        cls.ensure_worker_running()
-
-        enqueued_tasks = []
-        now = time.time()
-        endpoint = current_adb_endpoint()
-
+        session_id: str | None,
+        device_serial: str | None,
+        endpoint: AdbEndpoint,
+        now: float,
+    ) -> dict[str, Any] | None:
+        """Return the short-circuit response for a duplicate submission, if any."""
         # 1. Deduplication by session_id: if session_id is already running or queued, do not re-enqueue
         if session_id and len(goals) == 1:
             target_sid = str(session_id)
@@ -786,7 +760,13 @@ class TaskQueueService:
                     "enqueued_count": 0,
                     "total_queued": len(state.queue_tasks),
                 }
+        return None
 
+    @classmethod
+    async def _reject_unavailable_device(
+        cls, device_serial: str | None
+    ) -> dict[str, Any] | None:
+        """Return the rejection response for an unattached explicit serial, if any."""
         # Strict device binding: reject an explicitly requested serial that is not
         # attached and authorized, instead of silently running on another device.
         # The shared validator fails open on an indeterminate/empty enumeration so
@@ -806,9 +786,27 @@ class TaskQueueService:
                     "enqueued_count": 0,
                     "total_queued": len(state.queue_tasks),
                 }
+        return None
 
-        for i, goal in enumerate(goals):
-            sess_id = (session_id if (session_id and len(goals) == 1) else str(uuid.uuid4()))
+    @classmethod
+    def _create_queue_item(
+        cls,
+        goal: str,
+        index: int,
+        now: float,
+        endpoint: AdbEndpoint,
+        single_session_id: str | None,
+        profile: str,
+        expected_output: str | None,
+        enable_outputter: bool | None,
+        locked_app_package: str | None,
+        app_path: str | None,
+        device_serial: str | None,
+        ingress: str,
+        conversation_id: str | None,
+    ) -> dict[str, Any]:
+        """Reserve a device slot and build one pending queue item for a goal."""
+        sess_id = single_session_id if single_session_id else str(uuid.uuid4())
         assigned_serial = device_serial
         if not assigned_serial:
             try:
@@ -825,7 +823,7 @@ class TaskQueueService:
             ingress=ingress,
             lock_scope=endpoint.identity,
         )
-            task_item = {
+        return {
             "session_id": sess_id,
             "goal": goal,
             "profile": profile or "flash",
@@ -839,13 +837,62 @@ class TaskQueueService:
             "conversation_id": conversation_id,
             "status": "pending",
             "queue_ticket": queue_ticket,
-                "created_at": now + i * 0.001,
-                "start_time": now + i * 0.001,
+            "created_at": now + index * 0.001,
+            "start_time": now + index * 0.001,
         }
+
+    @classmethod
+    async def enqueue_tasks(
+        cls,
+        goals: list[str],
+        profile: str = "flash",
+        expected_output: str | None = None,
+        enable_outputter: bool | None = None,
+        locked_app_package: str | None = None,
+        app_path: str | None = None,
+        device_serial: str | None = None,
+        ingress: str = "frontend",
+        session_id: str | None = None,
+        conversation_id: str | None = None,
+    ) -> dict[str, Any]:
+        """Enqueues one or more goals and wakes up the background worker."""
+        cls.ensure_worker_running()
+
+        enqueued_tasks = []
+        now = time.time()
+        endpoint = current_adb_endpoint()
+
+        duplicate_response = cls._find_duplicate_submission(
+            goals, session_id, device_serial, endpoint, now
+        )
+        if duplicate_response is not None:
+            return duplicate_response
+
+        rejection_response = await cls._reject_unavailable_device(device_serial)
+        if rejection_response is not None:
+            return rejection_response
+
+        single_session_id = session_id if (session_id and len(goals) == 1) else None
+        for i, goal in enumerate(goals):
+            task_item = cls._create_queue_item(
+                goal,
+                i,
+                now,
+                endpoint,
+                single_session_id,
+                profile,
+                expected_output,
+                enable_outputter,
+                locked_app_package,
+                app_path,
+                device_serial,
+                ingress,
+                conversation_id,
+            )
             state.queue_items.append(task_item)
             enqueued_tasks.append(task_item)
             cls._broadcast_startup_progress(
-                sess_id, "queued", "Task received and queued"
+                task_item["session_id"], "queued", "Task received and queued"
             )
 
         # Wake worker immediately
@@ -858,36 +905,20 @@ class TaskQueueService:
             "total_queued": len(state.queue_tasks),
         }
 
+    @staticmethod
+    def _clear_pause_file() -> None:
+        """Remove a leftover pause marker after a stop request."""
+        if PAUSE_FILE.exists():
+            try:
+                PAUSE_FILE.unlink()
+            except OSError:
+                # Best-effort cleanup of the pause marker; a leftover file
+                # only pauses until the next resume request.
+                pass
+
     @classmethod
-    def stop_tasks(
-        cls,
-        clear_all: bool = False,
-        session_id: str | None = None,
-        device_id: str | None = None,
-    ) -> bool:
-        """Stop the active task controlling a mobile device or all tasks.
-
-        The active lease is shared by frontend, MCP, CLI, SDK, and other UI
-        processes across all connected devices.
-        - If ``session_id`` or ``device_id`` is specified, only the corresponding
-          running or queued task is cancelled.
-        - If ``clear_all`` is requested, all active device owners are terminated
-          and pending queue submissions are cleared.
-        - If no specific task is specified and ``clear_all`` is False, stops the
-          currently active task in single-device mode for backward compatibility.
-        """
-        stopped = False
-        target_sid = str(session_id).strip() if session_id else None
-        target_device = str(device_id).strip() if device_id else None
-
-        if clear_all:
-            # 1. Cancel local queue reservations
-            for item in state.queue_items:
-                if isinstance(item, dict) and item.get("status") != "running":
-                    DeviceExecutionLock.cancel_reservation(item.get("queue_ticket"))
-            state.clear_queue()
-
-            # 2. Terminate all active owners across all devices
+    def _terminate_all_device_owners(cls) -> None:
+        """Terminate every device lock owner and persist each cancellation."""
         active_owners: dict[str, Any] = {}
         try:
             active_owners = DeviceExecutionLock.get_active_owners()
@@ -929,6 +960,9 @@ class TaskQueueService:
                         },
                     )
 
+    @classmethod
+    def _kill_all_local_runs(cls) -> None:
+        """Mark every locally-managed run manually stopped and kill its process."""
         for run_key, run in list(state.active_runs.items()):
             # Mark each run individually: the global "stopped manually"
             # boolean was shared process-wide and polluted the terminal
@@ -955,31 +989,38 @@ class TaskQueueService:
                 pass
             state.current_process = None
 
+    @classmethod
+    def _stop_all_tasks(cls) -> bool:
+        """Terminate all active device owners and clear pending queue submissions."""
+        # 1. Cancel local queue reservations
+        for item in state.queue_items:
+            if isinstance(item, dict) and item.get("status") != "running":
+                DeviceExecutionLock.cancel_reservation(item.get("queue_ticket"))
+        state.clear_queue()
+
+        # 2. Terminate all active owners across all devices
+        cls._terminate_all_device_owners()
+        cls._kill_all_local_runs()
+
         state.active_connections.clear()
         state.active_session_id = None
         state.current_goal = None
         state.current_profile = None
 
-            if PAUSE_FILE.exists():
-                try:
-                    PAUSE_FILE.unlink()
-                except OSError:
-                    # Best-effort cleanup of the pause marker; a leftover file
-                    # only pauses until the next resume request.
-                    pass
+        cls._clear_pause_file()
 
         cls.ensure_worker_running()
         state.wake_event.set()
         return True
 
-        # Stop a specific task (or default single-device active task)
-        active_owners = {}
-        try:
-            active_owners = DeviceExecutionLock.get_active_owners()
-        except OSError as exc:
-            # Unreadable lock dir: the local-process fallbacks below still apply.
-            print(f"[stop_tasks] Could not enumerate device owners: {exc}")
-
+    @classmethod
+    def _resolve_stop_owner(
+        cls,
+        active_owners: dict[str, Any],
+        target_sid: str | None,
+        target_device: str | None,
+    ) -> Any:
+        """Resolve the device lock owner targeted by this stop request, if any."""
         owner = None
         if target_sid:
             for dev_owner in active_owners.values():
@@ -1003,12 +1044,17 @@ class TaskQueueService:
                 or (fallback_owner.session_id and str(fallback_owner.session_id) == target_sid)
             ):
                 owner = fallback_owner
+        return owner
 
-        owner_record_exists = DeviceExecutionLock.has_owner_record(target_device)
-        owner_pid = owner.pid if owner else None
+    @classmethod
+    def _resolve_local_run(
+        cls, target_sid: str | None, target_device: str | None
+    ) -> tuple[str | None, dict[str, Any] | None, Any]:
+        """Resolve the locally-managed run for this target.
 
-        # Resolve the locally-managed run for this target (concurrent scheduling
-        # keeps one subprocess per run in state.active_runs).
+        Concurrent scheduling keeps one subprocess per run in
+        state.active_runs. Returns ``(local_run_key, local_run, local_proc)``.
+        """
         local_run = None
         local_run_key: str | None = None
         if target_sid:
@@ -1047,9 +1093,11 @@ class TaskQueueService:
                 ),
                 None,
             )
-        local_pid = getattr(local_proc, "pid", None)
-        is_local_owner = bool(owner_pid and local_pid and owner_pid == local_pid)
+        return local_run_key, local_run, local_proc
 
+    @classmethod
+    def _find_target_queue_item(cls, target_sid: str | None) -> dict[str, Any] | None:
+        """Find the running (preferred) or pending queue item for this target."""
         running_item = next(
             (
                 item
@@ -1060,7 +1108,7 @@ class TaskQueueService:
             ),
             None,
         )
-        local_item = running_item or next(
+        return running_item or next(
             (
                 item
                 for item in state.queue_items
@@ -1070,10 +1118,21 @@ class TaskQueueService:
             ),
             None,
         )
+
+    @classmethod
+    def _resolve_stopped_session_id(
+        cls,
+        owner: Any,
+        target_sid: str | None,
+        local_run_key: str | None,
+        is_local_owner: bool,
+        local_item: dict[str, Any] | None,
+    ) -> Any:
+        """Attribute the stop request to a session id, if one can be resolved."""
         # active_session_id mirrors the most recently launched run, so with
         # concurrent runs the resolved local run key (== its session id) must
         # take precedence to avoid attributing the stop to an unrelated run.
-        stopped_session_id = (
+        return (
             owner.session_id
             if owner and owner.session_id
             else target_sid
@@ -1087,6 +1146,25 @@ class TaskQueueService:
             else None
         )
 
+    @classmethod
+    def _terminate_stop_target(
+        cls,
+        owner: Any,
+        owner_record_exists: bool,
+        target_sid: str | None,
+        local_run: dict[str, Any] | None,
+        local_run_key: str | None,
+        local_proc: Any,
+        local_pid: Any,
+        local_item: dict[str, Any] | None,
+        is_local_owner: bool,
+    ) -> tuple[bool, bool, bool] | None:
+        """Terminate the resolved stop target.
+
+        Returns ``(stopped, is_local_owner, reservation_cancelled)``, or
+        ``None`` when the caller must refuse the stop outright.
+        """
+        stopped = False
         reservation_cancelled = False
         if owner and DeviceExecutionLock.is_active_owner(owner):
             stopped = process_supervisor.terminate_tree_verified(
@@ -1097,7 +1175,7 @@ class TaskQueueService:
         elif owner is None and owner_record_exists and not target_sid:
             # Never fall back to a frontend PID while another process has an
             # owner record that is still being published or cannot be parsed.
-            return False
+            return None
         elif owner is None and local_proc is not None and (
             local_run is not None
             or not target_sid
@@ -1156,10 +1234,19 @@ class TaskQueueService:
                             )
                     DeviceExecutionLock.cleanup_stale_locks()
                     stopped = True
+        return stopped, is_local_owner, reservation_cancelled
 
-        if not stopped and not target_sid:
-            return False
-
+    @classmethod
+    def _finalize_targeted_stop(
+        cls,
+        stopped_session_id: Any,
+        owner: Any,
+        owner_pid: Any,
+        is_local_owner: bool,
+        local_run_key: str | None,
+        local_proc: Any,
+    ) -> None:
+        """Propagate the stop into shared state, the DB, and event subscribers."""
         if is_local_owner:
             if stopped_session_id:
                 # Per-session cancellation: the run's own finalizer resolves the
@@ -1207,7 +1294,13 @@ class TaskQueueService:
             state.current_goal = None
             state.current_profile = None
 
-        if stopped_session_id:
+    @classmethod
+    def _remove_stopped_queue_item(
+        cls, stopped_session_id: Any, reservation_cancelled: bool
+    ) -> None:
+        """Drop the stopped session's queue item and cancel its reservation."""
+        if not stopped_session_id:
+            return
         stopped_item = next(
             (
                 item
@@ -1228,18 +1321,94 @@ class TaskQueueService:
             )
         ]
 
-        if PAUSE_FILE.exists():
+    @classmethod
+    def _stop_targeted_task(
+        cls, target_sid: str | None, target_device: str | None
+    ) -> bool:
+        """Stop a specific task (or default single-device active task)."""
+        active_owners = {}
         try:
-                PAUSE_FILE.unlink()
-            except OSError:
-                # Best-effort cleanup of the pause marker; a leftover file
-                # only pauses until the next resume request.
-                pass
+            active_owners = DeviceExecutionLock.get_active_owners()
+        except OSError as exc:
+            # Unreadable lock dir: the local-process fallbacks below still apply.
+            print(f"[stop_tasks] Could not enumerate device owners: {exc}")
+
+        owner = cls._resolve_stop_owner(active_owners, target_sid, target_device)
+
+        owner_record_exists = DeviceExecutionLock.has_owner_record(target_device)
+        owner_pid = owner.pid if owner else None
+
+        local_run_key, local_run, local_proc = cls._resolve_local_run(
+            target_sid, target_device
+        )
+        local_pid = getattr(local_proc, "pid", None)
+        is_local_owner = bool(owner_pid and local_pid and owner_pid == local_pid)
+
+        local_item = cls._find_target_queue_item(target_sid)
+        stopped_session_id = cls._resolve_stopped_session_id(
+            owner, target_sid, local_run_key, is_local_owner, local_item
+        )
+
+        outcome = cls._terminate_stop_target(
+            owner,
+            owner_record_exists,
+            target_sid,
+            local_run,
+            local_run_key,
+            local_proc,
+            local_pid,
+            local_item,
+            is_local_owner,
+        )
+        if outcome is None:
+            return False
+        stopped, is_local_owner, reservation_cancelled = outcome
+
+        if not stopped and not target_sid:
+            return False
+
+        cls._finalize_targeted_stop(
+            stopped_session_id,
+            owner,
+            owner_pid,
+            is_local_owner,
+            local_run_key,
+            local_proc,
+        )
+        cls._remove_stopped_queue_item(stopped_session_id, reservation_cancelled)
+
+        cls._clear_pause_file()
 
         cls.ensure_worker_running()
         state.wake_event.set()
         return True
 
+    @classmethod
+    def stop_tasks(
+        cls,
+        clear_all: bool = False,
+        session_id: str | None = None,
+        device_id: str | None = None,
+    ) -> bool:
+        """Stop the active task controlling a mobile device or all tasks.
+
+        The active lease is shared by frontend, MCP, CLI, SDK, and other UI
+        processes across all connected devices.
+        - If ``session_id`` or ``device_id`` is specified, only the corresponding
+          running or queued task is cancelled.
+        - If ``clear_all`` is requested, all active device owners are terminated
+          and pending queue submissions are cleared.
+        - If no specific task is specified and ``clear_all`` is False, stops the
+          currently active task in single-device mode for backward compatibility.
+        """
+        target_sid = str(session_id).strip() if session_id else None
+        target_device = str(device_id).strip() if device_id else None
+
+        if clear_all:
+            return cls._stop_all_tasks()
+
+        return cls._stop_targeted_task(target_sid, target_device)
+
 
     @classmethod
     def resume_task(cls) -> bool:

apps/admin_console/services/worker_process_io.py

@@ -0,0 +1,146 @@
+# 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.
+
+"""Low-level worker subprocess I/O plumbing for the task queue.
+
+These helpers are deliberately free of admin-console state: they deal only
+with spawning options, output forwarding, and process-exit observation for a
+single worker subprocess. TaskQueueService exposes them as its private
+static methods so existing callers and tests keep working unchanged.
+"""
+
+import asyncio
+import codecs
+import os
+import psutil
+import subprocess
+import sys
+from typing import Any
+
+
+def subprocess_creation_kwargs() -> dict[str, Any]:
+    """Isolate task workers from the UI server's Windows console.
+
+    A new process group alone is insufficient on Windows: the worker still
+    shares the parent's console, so a CTRL_C_EVENT generated anywhere in
+    that console can reach the UI server. CREATE_NO_WINDOW removes that
+    shared console boundary.
+
+    Output is captured on every platform so it can be forwarded to the
+    server terminal and teed into the trace's stdout.log (the daemon itself
+    is often spawned with its stdio discarded, so inheriting would lose the
+    worker's logs entirely).
+    """
+    kwargs: dict[str, Any] = {
+        "stdout": asyncio.subprocess.PIPE,
+        "stderr": asyncio.subprocess.STDOUT,
+    }
+    if sys.platform == "win32":
+        kwargs["creationflags"] = (
+            subprocess.CREATE_NEW_PROCESS_GROUP | subprocess.CREATE_NO_WINDOW
+        )
+    return kwargs
+
+
+async def forward_worker_output(
+    stream: asyncio.StreamReader | None, log_path: str | None = None
+) -> None:
+    """Forward a worker's combined output without corrupting UTF-8.
+
+    When ``log_path`` is given, the output is also teed into that file so
+    the trace's advertised stdout.log actually exists for diagnostics.
+    """
+    if stream is None:
+        return
+
+    log_file = None
+    if log_path:
+        try:
+            os.makedirs(os.path.dirname(log_path), exist_ok=True)
+            log_file = open(log_path, "w", buffering=1, encoding="utf-8", errors="replace")
+        except Exception as exc:
+            print(f"[QueueWorker] Could not open worker log file '{log_path}': {exc}")
+
+    def _emit(text: str) -> None:
+        sys.stdout.write(text)
+        sys.stdout.flush()
+        if log_file is not None:
+            try:
+                log_file.write(text)
+            except (OSError, ValueError):
+                # Best-effort tee into stdout.log; console output above
+                # already carried the text.
+                pass
+
+    try:
+        decoder = codecs.getincrementaldecoder("utf-8")(errors="replace")
+        while True:
+            chunk = await stream.read(4096)
+            if not chunk:
+                break
+            text = decoder.decode(chunk)
+            if text:
+                _emit(text)
+
+        tail = decoder.decode(b"", final=True)
+        if tail:
+            _emit(tail)
+    finally:
+        if log_file is not None:
+            try:
+                log_file.close()
+            except OSError:
+                # Flush-on-close of the best-effort tee failed; nothing to do.
+                pass
+
+
+async def finish_output_forwarder(output_task: asyncio.Task[None] | None) -> None:
+    """Drain final worker output without allowing inherited handles to stall the queue."""
+    if output_task is None:
+        return
+    try:
+        await asyncio.wait_for(asyncio.shield(output_task), timeout=2.0)
+    except asyncio.CancelledError:
+        if output_task.cancelled():
+            return
+        raise
+    except TimeoutError:
+        output_task.cancel()
+        try:
+            await output_task
+        except asyncio.CancelledError:
+            pass
+    except Exception as exc:
+        print(f"[QueueWorker] Failed to forward detached worker output: {exc}")
+
+
+async def wait_for_worker_process(proc: asyncio.subprocess.Process) -> int:
+    """Wait for worker process to exit, with watchdog fallback if PID was reaped externally."""
+    while True:
+        try:
+            return await asyncio.wait_for(proc.wait(), timeout=1.0)
+        except TimeoutError:
+            pid = getattr(proc, "pid", None)
+            if pid:
+                try:
+                    p = psutil.Process(pid)
+                    if not p.is_running() or p.status() == psutil.STATUS_ZOMBIE:
+                        return proc.returncode if proc.returncode is not None else -15
+                except (psutil.NoSuchProcess, ProcessLookupError):
+                    return proc.returncode if proc.returncode is not None else -15
+                except psutil.Error:
+                    # Transient probe failure (e.g. AccessDenied): keep waiting.
+                    pass
+            else:
+                return proc.returncode if proc.returncode is not None else -15