Developer's trading bot silently held a delisted stock for months due to a data-gap bug

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A software developer discovered that his AI-powered trading bot had been indefinitely holding a delisted stock without attempting to sell it. The bug stemmed from a code condition that required at least 260 days of historical price data before a stock could be considered for an exit decision. When the stock was delisted, its data disappeared from the historical API, causing the bot to silently skip it rather than raise an error. The issue was compounded by the bot using two separate APIs — one for trade decisions and another for portfolio valuation — which created an undetected inconsistency between a 'non-existent' stock and an 'owned' position. The developer fixed the flaw by reversing the logic flow: instead of filtering stocks by data availability first, the bot now starts with current holdings and flags any position with missing or stale data as an abnormal situation requiring immediate action.

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