feat(signal_v2): rate_limit + 3 unit tests

SignalDedup: 24h-rolling duplicate signal blocker. SQLite WAL +
busy_timeout=120000 standard fix (reference_sqlite_concurrency.md
pattern). PK (ticker, action) with UPSERT. Phase 4 (signal generator)
will call is_recent() before sending + record() after sending.

3 unit tests pass, total 17 signal_v2.

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

signal_v2/rate_limit.py

@@ -0,0 +1,73 @@
+"""SignalDedup — SQLite-backed 24h duplicate signal blocker."""
+from __future__ import annotations
+import sqlite3
+from contextlib import contextmanager
+from datetime import datetime, timedelta
+from pathlib import Path
+from zoneinfo import ZoneInfo
+
+KST = ZoneInfo("Asia/Seoul")
+
+
+def _now_iso() -> str:
+    """Test seam — overridable via monkeypatch."""
+    return datetime.now(KST).isoformat()
+
+
+_SCHEMA = """
+CREATE TABLE IF NOT EXISTS signal_dedup (
+    ticker      TEXT NOT NULL,
+    action      TEXT NOT NULL,
+    last_sent   TEXT NOT NULL,
+    confidence  REAL NOT NULL,
+    PRIMARY KEY (ticker, action)
+);
+CREATE INDEX IF NOT EXISTS idx_signal_dedup_last_sent
+    ON signal_dedup(last_sent);
+"""
+
+
+class SignalDedup:
+    """24h dedup interface. WAL + busy_timeout=120000."""
+
+    def __init__(self, db_path: Path):
+        self._db_path = Path(db_path)
+        self._db_path.parent.mkdir(parents=True, exist_ok=True)
+        self._init_schema()
+
+    @contextmanager
+    def _conn(self):
+        conn = sqlite3.connect(self._db_path, timeout=120.0)
+        try:
+            conn.execute("PRAGMA journal_mode=WAL")
+            conn.execute("PRAGMA busy_timeout=120000")
+            yield conn
+        finally:
+            conn.close()
+
+    def _init_schema(self) -> None:
+        with self._conn() as conn:
+            conn.executescript(_SCHEMA)
+            conn.commit()
+
+    def is_recent(self, ticker: str, action: str, within_hours: int = 24) -> bool:
+        threshold_dt = datetime.fromisoformat(_now_iso()) - timedelta(hours=within_hours)
+        threshold_iso = threshold_dt.isoformat()
+        with self._conn() as conn:
+            row = conn.execute(
+                "SELECT last_sent FROM signal_dedup WHERE ticker = ? AND action = ?",
+                (ticker, action),
+            ).fetchone()
+        return row is not None and row[0] >= threshold_iso
+
+    def record(self, ticker: str, action: str, confidence: float) -> None:
+        with self._conn() as conn:
+            conn.execute(
+                """INSERT INTO signal_dedup (ticker, action, last_sent, confidence)
+                   VALUES (?, ?, ?, ?)
+                   ON CONFLICT (ticker, action) DO UPDATE
+                   SET last_sent = excluded.last_sent,
+                       confidence = excluded.confidence""",
+                (ticker, action, _now_iso(), confidence),
+            )
+            conn.commit()

signal_v2/tests/test_rate_limit.py

@@ -0,0 +1,34 @@
+"""Tests for SignalDedup."""
+from datetime import datetime, timedelta
+from zoneinfo import ZoneInfo
+
+from signal_v2.rate_limit import SignalDedup
+
+KST = ZoneInfo("Asia/Seoul")
+
+
+def test_is_recent_returns_false_for_new_ticker_action(tmp_dedup_db):
+    dedup = SignalDedup(tmp_dedup_db)
+    assert dedup.is_recent("005930", "buy") is False
+
+
+def test_is_recent_returns_true_within_24h(tmp_dedup_db):
+    dedup = SignalDedup(tmp_dedup_db)
+    dedup.record("005930", "buy", confidence=0.82)
+    assert dedup.is_recent("005930", "buy") is True
+
+
+def test_is_recent_returns_false_after_24h(tmp_dedup_db, monkeypatch):
+    dedup = SignalDedup(tmp_dedup_db)
+    # Record with a timestamp 25 hours ago
+    now = datetime.now(KST)
+    fake_now = now - timedelta(hours=25)
+    monkeypatch.setattr(
+        "signal_v2.rate_limit._now_iso", lambda: fake_now.isoformat()
+    )
+    dedup.record("005930", "buy", confidence=0.82)
+    # Reset to real now for is_recent check
+    monkeypatch.setattr(
+        "signal_v2.rate_limit._now_iso", lambda: now.isoformat()
+    )
+    assert dedup.is_recent("005930", "buy", within_hours=24) is False