Add tools/undervalued.py: trading strategy, goods priced below production cost

Finds manufactured goods currently selling below their implied
production cost (live input cost vs output price) - candidates to buy
and hold for a price-reversion bounce, the mirror of the "is this
worth building" question saturation.py already answers.

Backtested first (326 output tickers, 287 deduplicated dip-onset
episodes across 112 distinct tickers): +3mo forward return mean
+21.3%/median +8.9%/73.2% hit rate at >=10 units/day volume - real
signal, not noise, but only ~0.10-0.24%/day, far below the 14-29%/day
marginal ROI this session's production builds found. Documented
prominently in the tool's own docstring and CLAUDE.md so it doesn't
get mistaken for a primary strategy - it's for excess idle capital
once better-yielding builds are exhausted, not before.

Promoted daily_prices() out of tools/history.py into puga/history.py
so both tools share it, per the self-improve rule.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tools/undervalued.py

@@ -0,0 +1,41 @@
+#!/usr/bin/env python3
+"""Manufactured goods currently selling below their implied production cost (output price minus
+live input cost) - candidates to buy and hold for a price-reversion bounce, not to build.
+
+EXPECTED ROI IS MUCH LOWER THAN THIS PROJECT'S PRODUCTION BUILDS. Backtest (2026-10-09, 326
+output tickers, 287 independent dip-onset episodes across 112 distinct tickers, >=10 units/day
+volume): +3 months forward price return mean +21.3%, median +8.9%, 73.2% of episodes positive.
+That's ~0.10-0.24%/day, or very roughly ~41%/year if you could always immediately redeploy into
+a new dip (optimistic) - versus 14-29%/day marginal ROI on the production buildings this toolkit
+has been recommending. Gross price return only, no spread/freight/storage-fee/capital-lockup cost
+subtracted. Only deploy EXCESS capital here once better-yielding builds are exhausted - this is
+not a primary strategy.
+
+  tools/undervalued.py                    # AI1, min 5 units/day traded
+  tools/undervalued.py --cx AI1 --min-vol 10 --top 10
+"""
+import argparse, sys
+from pathlib import Path
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
+from puga import config, undervalued
+
+
+def main():
+    ap = argparse.ArgumentParser()
+    ap.add_argument("--cx", default=config.DEFAULT_CX)
+    ap.add_argument("--min-vol", type=float, default=5.0, help="min units/day traded (noise filter, thin markets won't revert reliably)")
+    ap.add_argument("--top", type=int, default=20)
+    a = ap.parse_args()
+
+    rows = undervalued.scan_current(a.cx, a.min_vol)
+    if not rows:
+        print(f"nothing currently priced below production cost at {a.cx} with volume >= {a.min_vol}/day")
+        return
+    print(f"# {a.cx}  min-vol>={a.min_vol}/day  (gross price return only - see docstring for backtest caveats)")
+    print(f"{'ticker':6} {'margin%':>8} {'price':>10} {'vol/d':>7}  bld")
+    for r in rows[:a.top]:
+        print(f"{r['ticker']:6} {r['margin_pct']:8.1f} {r['price']:10.1f} {r['volume']:7.1f}  {r['building']}")
+
+
+if __name__ == "__main__":
+    main()