VIOLET research TODO: why does unguarded IRP pick stablecoins?

Logs the open question (noise/denominator artifact vs real depeg micro-edge
deliberately self-limited) + how to settle it. VIOLET keeps BLUE's exclusion
regardless (follow BLUE).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

prod/docs/VIOLET_RESEARCH_TODO__STABLECOIN_IRP_SIGNAL.md

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+# VIOLET Research TODO — Why does the IRP pick stablecoins when unguarded?
+
+**Status:** Research TODO (logged 2026-06-14). Low priority, high curiosity. Not blocking.
+
+## Observation
+
+The VIOLET shadow soak, running BLUE's muted-IRP gold config (`min_irp_alignment=0.0`)
+WITHOUT BLUE's stablecoin exclusion gate, repeatedly ranked **USDCUSDT** top and would
+have shorted it at full conviction (9.0). BLUE hardcodes these out
+(`_STABLECOIN_SYMBOLS`, nautilus_event_trader.py:24/3906 — "must never be traded"), and
+VIOLET now replicates that (commit V3.1). So in production it's correctly excluded.
+
+## The question
+
+**Why does the IRP ranker select stablecoins when unguarded — and is the exclusion
+leaving a real (small, desirable-to-forgo) edge on the table?**
+
+Two hypotheses:
+1. **Noise/artifact.** Stablecoin price series are near-flat; the IRP efficiency/ARS
+   metric may divide by a tiny denominator (low realized vol), inflating the score on
+   essentially flat micro-movements → a spurious "clean signal." If so, exclusion is pure
+   correctness (avoids dividing-by-near-zero noise).
+2. **Real micro-edge, deliberately self-limited.** Stablecoin depeg oscillations
+   (USDC/USDT wobbling around \$1) are mean-reverting and genuinely tradeable at tiny
+   size — the IRP may be detecting a real, low-volatility, low-risk signal. BLUE's
+   exclusion would then be forgoing a small but real edge BY DESIGN (correctly — pegged
+   assets carry depeg tail risk, poor borrow, regulatory/operational hazards that dwarf
+   the micro-edge; not worth it).
+
+## How to settle it (when researched)
+
+- Backtest the EXCLUDED stablecoin picks as if traded (small size): realized PnL,
+  Sharpe, max depeg drawdown, borrow/funding cost. Does the micro-edge survive costs +
+  the depeg tail?
+- Inspect the IRP ARS/efficiency computation on flat series (rank_assets_irp_nb): is the
+  high score a denominator artifact (hypothesis 1) or a real efficiency signal (2)?
+- Cross-check against the dual-leverage/conviction the sizer assigns (it gave conviction
+  9 on USDC vel_div −0.0585 — is that vel_div itself an artifact of a flat series?).
+
+## Why it matters (mildly)
+
+If hypothesis 2 holds, it informs whether a *separate, tiny-size, depeg-aware*
+stablecoin strategy could be a future color — orthogonal to BLUE's directional short
+edge. If hypothesis 1, it's just confirmation the exclusion is correctness. Either way,
+VIOLET keeps the exclusion (follow BLUE). See
+[[blue_margin_envelope_study]], [[violet_v3_alpha_doctrine]] (#12 follow-BLUE).