feat: implement latency control system with criticality-based prioritization

Add urgency-based response system to react faster in critical market situations.

Components:
- CriticalityAssessor: Evaluates market conditions (P&L, volatility, volume surge)
  and assigns urgency levels (CRITICAL <5s, HIGH <30s, NORMAL <60s, LOW batch)
- PriorityTaskQueue: Thread-safe priority queue with timeout enforcement,
  metrics tracking, and graceful degradation when full
- Integration with main.py: Assess criticality at trading cycle start,
  monitor latency per criticality level, log queue metrics

Auto-elevate to CRITICAL when:
- P&L < -2.5% (near circuit breaker at -3.0%)
- Stock moves >5% in 1 minute
- Volume surge >10x average

Integration with Volatility Hunter:
- Uses VolatilityAnalyzer.calculate_momentum() for assessment
- Pulls volatility scores from Context Tree L7_REALTIME
- Auto-detects market conditions for criticality

Tests:
- 30 comprehensive tests covering criticality assessment, priority queue,
  timeout enforcement, metrics tracking, and integration scenarios
- Coverage: criticality.py 100%, priority_queue.py 96%
- All 157 tests pass

Resolves issue #21 - Pillar 1: 속도와 시의성의 최적화

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/core/priority_queue.py

@@ -0,0 +1,291 @@
+"""Priority-based task queue for latency control.
+
+Implements a thread-safe priority queue with timeout enforcement and metrics tracking.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import heapq
+import logging
+import time
+from collections.abc import Callable, Coroutine
+from dataclasses import dataclass, field
+from typing import Any
+
+from src.core.criticality import CriticalityLevel
+
+logger = logging.getLogger(__name__)
+
+
+@dataclass(order=True)
+class PriorityTask:
+    """Task with priority and timestamp for queue ordering."""
+
+    # Lower priority value = higher urgency (CRITICAL=0, HIGH=1, NORMAL=2, LOW=3)
+    priority: int
+    timestamp: float
+    # Task data not used in comparison
+    task_id: str = field(compare=False)
+    task_data: dict[str, Any] = field(compare=False, default_factory=dict)
+    callback: Callable[[], Coroutine[Any, Any, Any]] | None = field(
+        compare=False, default=None
+    )
+
+
+@dataclass
+class QueueMetrics:
+    """Metrics for priority queue performance monitoring."""
+
+    total_enqueued: int = 0
+    total_dequeued: int = 0
+    total_timeouts: int = 0
+    total_errors: int = 0
+    current_size: int = 0
+    # Average wait time per criticality level (in seconds)
+    avg_wait_time: dict[CriticalityLevel, float] = field(default_factory=dict)
+    # P95 wait time per criticality level
+    p95_wait_time: dict[CriticalityLevel, float] = field(default_factory=dict)
+
+
+class PriorityTaskQueue:
+    """Thread-safe priority queue with timeout enforcement."""
+
+    # Priority mapping for criticality levels
+    PRIORITY_MAP = {
+        CriticalityLevel.CRITICAL: 0,
+        CriticalityLevel.HIGH: 1,
+        CriticalityLevel.NORMAL: 2,
+        CriticalityLevel.LOW: 3,
+    }
+
+    def __init__(self, max_size: int = 1000) -> None:
+        """Initialize the priority task queue.
+
+        Args:
+            max_size: Maximum queue size (default 1000)
+        """
+        self._queue: list[PriorityTask] = []
+        self._lock = asyncio.Lock()
+        self._max_size = max_size
+        self._metrics = QueueMetrics()
+        # Track wait times for metrics
+        self._wait_times: dict[CriticalityLevel, list[float]] = {
+            level: [] for level in CriticalityLevel
+        }
+
+    async def enqueue(
+        self,
+        task_id: str,
+        criticality: CriticalityLevel,
+        task_data: dict[str, Any],
+        callback: Callable[[], Coroutine[Any, Any, Any]] | None = None,
+    ) -> bool:
+        """Add a task to the priority queue.
+
+        Args:
+            task_id: Unique identifier for the task
+            criticality: Criticality level determining priority
+            task_data: Data associated with the task
+            callback: Optional async callback to execute
+
+        Returns:
+            True if enqueued successfully, False if queue is full
+        """
+        async with self._lock:
+            if len(self._queue) >= self._max_size:
+                logger.warning(
+                    "Priority queue full (size=%d), rejecting task %s",
+                    len(self._queue),
+                    task_id,
+                )
+                return False
+
+            priority = self.PRIORITY_MAP[criticality]
+            timestamp = time.time()
+
+            task = PriorityTask(
+                priority=priority,
+                timestamp=timestamp,
+                task_id=task_id,
+                task_data=task_data,
+                callback=callback,
+            )
+
+            heapq.heappush(self._queue, task)
+            self._metrics.total_enqueued += 1
+            self._metrics.current_size = len(self._queue)
+
+            logger.debug(
+                "Enqueued task %s with criticality %s (priority=%d, queue_size=%d)",
+                task_id,
+                criticality.value,
+                priority,
+                len(self._queue),
+            )
+
+            return True
+
+    async def dequeue(self, timeout: float | None = None) -> PriorityTask | None:
+        """Remove and return the highest priority task from the queue.
+
+        Args:
+            timeout: Maximum time to wait for a task (seconds)
+
+        Returns:
+            PriorityTask if available, None if queue is empty or timeout
+        """
+        start_time = time.time()
+        deadline = start_time + timeout if timeout else None
+
+        while True:
+            async with self._lock:
+                if self._queue:
+                    task = heapq.heappop(self._queue)
+                    self._metrics.total_dequeued += 1
+                    self._metrics.current_size = len(self._queue)
+
+                    # Calculate wait time
+                    wait_time = time.time() - task.timestamp
+                    criticality = self._get_criticality_from_priority(task.priority)
+                    self._wait_times[criticality].append(wait_time)
+                    self._update_wait_time_metrics()
+
+                    logger.debug(
+                        "Dequeued task %s (priority=%d, wait_time=%.2fs, queue_size=%d)",
+                        task.task_id,
+                        task.priority,
+                        wait_time,
+                        len(self._queue),
+                    )
+
+                    return task
+
+            # Queue is empty
+            if deadline and time.time() >= deadline:
+                return None
+
+            # Wait a bit before checking again
+            await asyncio.sleep(0.1)
+
+    async def execute_with_timeout(
+        self,
+        task: PriorityTask,
+        timeout: float | None,
+    ) -> Any:
+        """Execute a task with timeout enforcement.
+
+        Args:
+            task: Task to execute
+            timeout: Timeout in seconds (None = no timeout)
+
+        Returns:
+            Result from task callback
+
+        Raises:
+            asyncio.TimeoutError: If task exceeds timeout
+            Exception: Any exception raised by the task callback
+        """
+        if not task.callback:
+            logger.warning("Task %s has no callback, skipping execution", task.task_id)
+            return None
+
+        criticality = self._get_criticality_from_priority(task.priority)
+
+        try:
+            if timeout:
+                result = await asyncio.wait_for(task.callback(), timeout=timeout)
+            else:
+                result = await task.callback()
+
+            logger.debug(
+                "Task %s completed successfully (criticality=%s)",
+                task.task_id,
+                criticality.value,
+            )
+            return result
+
+        except TimeoutError:
+            self._metrics.total_timeouts += 1
+            logger.error(
+                "Task %s timed out after %.2fs (criticality=%s)",
+                task.task_id,
+                timeout or 0.0,
+                criticality.value,
+            )
+            raise
+
+        except Exception as exc:
+            self._metrics.total_errors += 1
+            logger.exception(
+                "Task %s failed with error (criticality=%s): %s",
+                task.task_id,
+                criticality.value,
+                exc,
+            )
+            raise
+
+    def _get_criticality_from_priority(self, priority: int) -> CriticalityLevel:
+        """Convert priority back to criticality level."""
+        for level, prio in self.PRIORITY_MAP.items():
+            if prio == priority:
+                return level
+        return CriticalityLevel.NORMAL
+
+    def _update_wait_time_metrics(self) -> None:
+        """Update average and p95 wait time metrics."""
+        for level, times in self._wait_times.items():
+            if not times:
+                continue
+
+            # Keep only last 1000 measurements to avoid memory bloat
+            if len(times) > 1000:
+                self._wait_times[level] = times[-1000:]
+                times = self._wait_times[level]
+
+            # Calculate average
+            self._metrics.avg_wait_time[level] = sum(times) / len(times)
+
+            # Calculate P95
+            sorted_times = sorted(times)
+            p95_idx = int(len(sorted_times) * 0.95)
+            self._metrics.p95_wait_time[level] = sorted_times[p95_idx]
+
+    async def get_metrics(self) -> QueueMetrics:
+        """Get current queue metrics.
+
+        Returns:
+            QueueMetrics with current statistics
+        """
+        async with self._lock:
+            return QueueMetrics(
+                total_enqueued=self._metrics.total_enqueued,
+                total_dequeued=self._metrics.total_dequeued,
+                total_timeouts=self._metrics.total_timeouts,
+                total_errors=self._metrics.total_errors,
+                current_size=self._metrics.current_size,
+                avg_wait_time=dict(self._metrics.avg_wait_time),
+                p95_wait_time=dict(self._metrics.p95_wait_time),
+            )
+
+    async def size(self) -> int:
+        """Get current queue size.
+
+        Returns:
+            Number of tasks in queue
+        """
+        async with self._lock:
+            return len(self._queue)
+
+    async def clear(self) -> int:
+        """Clear all tasks from the queue.
+
+        Returns:
+            Number of tasks cleared
+        """
+        async with self._lock:
+            count = len(self._queue)
+            self._queue.clear()
+            self._metrics.current_size = 0
+            logger.info("Cleared %d tasks from priority queue", count)
+            return count