signal_log: persist every live scan (signal, grade, price, news) to SQLite

New signal_log.py logs each SignalReport to logs/signals.db via a
fail-safe hook in SignalAggregator.analyze_pair — the live-only entry
point used by the bot, daemon, CLI and dashboard. Backtester calls
analyze_from_dataframes directly, so live==backtest parity is preserved
(test-locked). Rows carry signal/grade/price/spread, MTF + trade-setup +
reasons/warnings JSON, and news-at-scan-time (calendar events + scored
headlines JSON via NewsEngine class-level caches).

Config: signal_log block (enabled, path; env SIGNAL_LOG_ENABLED/PATH),
source tagged per consumer (telegram/oanda_daemon/cli/dashboard).
381 tests pass (24 modules).

app_config.py

@@ -86,7 +86,7 @@ _VALID_LOG_LEVELS = ("DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL")
 _SCANNABLE_TFS = ("M5", "M15", "H1", "H4")
 
 _KNOWN_TOP = {"telegram", "data_providers", "scanning", "pairs", "log_level",
-              "oanda", "deepseek", "agent_panel"}
+              "oanda", "deepseek", "agent_panel", "signal_log"}
 _KNOWN_OANDA = {
     "account_id", "api_token", "base_url", "lot_size",
     "quality_gate", "max_hold_bars",
@@ -98,6 +98,7 @@ _KNOWN_AGENT_PANEL = {
     "enabled", "telegram", "dashboard", "min_quality",
     "max_panels_per_day", "reuse_ttl_seconds",
 }
+_KNOWN_SIGNAL_LOG = {"enabled", "path"}
 _KNOWN_TELEGRAM = {"token", "chat_id", "channel_id", "alert_min_quality"}
 _KNOWN_SCANNING = {"pairs", "timeframes"}
 _KNOWN_PAIR_KEYS = {"blocked_hours_utc"}
@@ -123,6 +124,7 @@ class AppConfig:
     oanda_settings: Dict[str, Any] = field(default_factory=dict)
     deepseek_settings: Dict[str, Any] = field(default_factory=dict)
     agent_panel_settings: Dict[str, Any] = field(default_factory=dict)
+    signal_log_settings: Dict[str, Any] = field(default_factory=dict)
     log_level: str = "INFO"
 
 
@@ -306,6 +308,17 @@ def load_app_config(path: str = CONFIG_PATH) -> AppConfig:
                 "non-negative number")
     app.agent_panel_settings = dict(panel)
 
+    slog = raw.get("signal_log", {})
+    _check_keys(slog, _KNOWN_SIGNAL_LOG, '"signal_log"')
+    if "enabled" in slog and not isinstance(slog["enabled"], bool):
+        raise AppConfigError(
+            "config.json: signal_log.enabled must be true or false")
+    if "path" in slog and (not isinstance(slog["path"], str)
+                           or not slog["path"]):
+        raise AppConfigError(
+            "config.json: signal_log.path must be a non-empty string")
+    app.signal_log_settings = dict(slog)
+
     level = raw.get("log_level", app.log_level)
     if level not in _VALID_LOG_LEVELS:
         raise AppConfigError(
@@ -405,6 +418,31 @@ def deepseek_api_key(app: Optional[AppConfig] = None) -> str:
         app.deepseek_settings.get("api_key", ""))
 
 
+# ── Signal-log resolution helpers (env → config.json → default) ──────
+
+def signal_log_enabled(app: Optional[AppConfig] = None) -> bool:
+    """Default ON — signal history is the platform's audit trail."""
+    env = os.environ.get("SIGNAL_LOG_ENABLED")
+    if env:
+        return env.strip().lower() in ("1", "true", "yes", "on")
+    app = app or get_app_config()
+    return bool(app.signal_log_settings.get("enabled", True))
+
+
+def signal_log_path(app: Optional[AppConfig] = None) -> str:
+    """Absolute path to the SQLite signal-history DB. A relative config
+    value resolves against the repo root so CWD never matters."""
+    env = os.environ.get("SIGNAL_LOG_PATH")
+    if env:
+        path = env
+    else:
+        app = app or get_app_config()
+        path = str(app.signal_log_settings.get("path", "logs/signals.db"))
+    if not os.path.isabs(path):
+        path = os.path.join(os.path.dirname(os.path.abspath(__file__)), path)
+    return path
+
+
 # ── PlatformConfig overlay ────────────────────────────────────────────
 
 def apply_pair_overrides(