1. executor.shutdown(wait=True) still blocked after global timeout (critical)
The previous fix added timeout= to as_completed() but used `with
ThreadPoolExecutor() as executor`, whose __exit__ calls shutdown(wait=True).
This meant the process still hung waiting for stuck threads (ml_signal) even
after the TimeoutError was caught. Fixed by creating the executor explicitly
and calling shutdown(wait=False) in a finally block.
2. ml_signal hangs on every run — "Batch-downloading 592 tickers (1y)..." never
completes. Root cause: a single yfinance request for 592 tickers × 1 year of
daily OHLCV is a very large payload that regularly times out at the network
layer. Fixed by:
- Reducing default lookback from "1y" to "6mo" (halves download size)
- Splitting downloads into 150-ticker chunks so a slow chunk doesn't kill
the whole scan (partial results are still returned)
3. C (Citigroup) and other single-letter NYSE tickers rejected as invalid.
validate_ticker_format used ^[A-Z]{2,5}$ requiring at least 2 letters.
Real tickers like C, A, F, T, X, M are 1 letter. Fixed to ^[A-Z]{1,5}$.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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