feat(ai_trade): state.signals에 expires_at + cycle_id lifecycle 추가 (F5 part 1)

코드 리뷰 F5 — Phase 5 consumer(agent-office /signal) prereq:
PollState.signal_cycle_id (process auto-increment) + get_active_signals(now) +
purge_expired_signals(now) helper. expires_at 없는 legacy signal은 expired 취급.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ai_trade/state.py

@@ -1,6 +1,7 @@
 """PollState — process-wide singleton."""
 from collections import deque
 from dataclasses import dataclass, field
+from datetime import datetime
 
 
 @dataclass
@@ -15,8 +16,44 @@ class PollState:
     chronos_predictions: dict[str, dict] = field(default_factory=dict)
     minute_momentum: dict[str, str] = field(default_factory=dict)
     signals: dict[str, dict] = field(default_factory=dict)
+    # F5 lifecycle
+    signal_cycle_id: int = 0
     last_updated: dict[str, str] = field(default_factory=dict)
     fetch_errors: dict[str, int] = field(default_factory=dict)
 
+    def get_active_signals(self, now: datetime) -> list[dict]:
+        """expires_at > now 인 신호만 반환. expires_at 없거나 파싱 실패는 expired 취급."""
+        active: list[dict] = []
+        for sig in self.signals.values():
+            expires_at = sig.get("expires_at")
+            if not expires_at:
+                continue
+            try:
+                exp_dt = datetime.fromisoformat(expires_at)
+            except ValueError:
+                continue
+            if exp_dt > now:
+                active.append(sig)
+        return active
+
+    def purge_expired_signals(self, now: datetime) -> int:
+        """만료된 signal 제거. expires_at 없거나 파싱 실패도 제거. 제거 개수 반환."""
+        to_drop = []
+        for ticker, sig in self.signals.items():
+            expires_at = sig.get("expires_at")
+            if not expires_at:
+                to_drop.append(ticker)
+                continue
+            try:
+                exp_dt = datetime.fromisoformat(expires_at)
+            except ValueError:
+                to_drop.append(ticker)
+                continue
+            if exp_dt <= now:
+                to_drop.append(ticker)
+        for t in to_drop:
+            del self.signals[t]
+        return len(to_drop)
+
 
 state = PollState()