Derive chart opens from first traded minute

[luisleo526]

Summary

• derive a 15-minute chart open from the first positive-volume 1-minute row, while retaining the first row for an all-zero bucket
• version the derived-feed cache so existing materializations rebuild once
• make atomic writes safe when two validators rebuild concurrently
• add focused feed, invalid-input, cache, and concurrency coverage

Why

The committed 1-minute feed contains Binance zero-volume continuity rows. TradingView uses the first real trade for the 15-minute open. At 2025-08-29 06:30 UTC, 4451.33 from seven leading zero-volume rows masked a strict bullish-engulfing edge; the first traded minute opens at 4451.32. The corrected feed restores the one missing Jos trade and makes the strategy exact at 2,207/2,207.

Only two derived opens change across 222,295 bars, one outside the comparison window. The committed 1-minute source is unchanged.

Validation

• focused derivation tests: 8/8
• Release CTest: 105/105
• pinned codegen: 1,537 passed / 2 skipped
• engine corpus: 252/252; 243 Excellent / 8 Strong / 1 expected anomaly
• forced-no-cache scraper sweep: 412 accounted; 403 OK / 1 no-trades / 7 transpile errors / 0 compile errors / 1 known run error
• tier diff: Jos Strong to Excellent; 1 UP / 0 DOWN
• final board: 340 Excellent / 52 Strong / 4 Moderate / 5 Weak, with 8 excluded

Derived full-feed SHA-256: 27b62431096edf1bfba71b2409f8dc183f69213dec2834560b3241750f8e7026.