EUR M15/H1 investigation: document no-validated-edge verdict

Five independent tests at 1-pip cost (M15 wide-open both windows,
transitioning-slice OOS, mean-reversion trade sims, forward-return
screens on M15+M5, H1 both windows) — nothing clears cost in both
2024-25 and 2025-26. Root cause: spread is ~10% of M15 ATR on EUR.
EUR stays out of scan_pairs; open avenues documented in docstring.

pair_signals/eurusd.py

@@ -15,10 +15,31 @@ branch's -6.7R. Findings that shaped them:
   - score 30-35 band is where the train-half losses live → floor 35
   - trailing exits beat static TP1 (arm 0.45R / dist 0.5R best)
 
+M15 + H1 investigated 2026-07-11, verdict NO VALIDATED EDGE either
+(all at 1-pip round-trip cost, real fills):
+  - M15 wide-open (all gates off): -2.5R/270 trades 2025-26;
+    -54.8R/308 trades on 2024-25 out-of-sample. PF 0.61-0.98.
+  - Best in-sample slice (transitioning-regime-only: +15.4R, PF 1.59,
+    positive both halves, month-spread) FAILED 2024-25 OOS at PF 0.55.
+    Within-year train/val splits are not sufficient for EUR — always
+    re-test on the 2024 window before believing a config.
+  - Raw-parquet forward-return screens (M15 and M5, ~14 entry
+    conditions x 4-5 horizons: momentum, mean-reversion, breakout,
+    streak, session families): nothing clears +1 pip in both years.
+  - H1 wide-open: +9.8R PF 1.32 in 2025-26 (both halves positive) but
+    -5.7R PF 0.82 on 2024-25. Positive from Jan 2025 onward; H2-2024
+    regime negative. Closest to workable, still unvalidated.
+
+Root cause is cost-to-volatility: EUR M15 ATR ~= 10 pips, so the 1-pip
+spread taxes every trade ~10% of ATR (M5 worse). The XAU signal engine
+survives because gold's ATR/spread ratio is several times larger.
+
 EUR/USD therefore ships FUNCTIONAL BUT OFF by default: it is not in
 PlatformConfig.scan_pairs. Scan it on demand (main.py --pair EURUSD,
-or add to scan_pairs) but do not treat M5 signals as having a
+or add to scan_pairs) but treat all EUR M5/M15 signals as informational
-validated edge. M15 tuning is a future session.
+only. Open avenues needing new data/infra: calendar-anchored entries
+(requires a historical Forex Factory archive), limit-entry cost
+reduction (needs tick data to model fills honestly), H4/D1 swing.
 """
 
 from typing import Optional, List