Warn on non-function useMemo first arg — DEV-only runtime warning

Frontend teams—especially large codebases with junior engineers, many third-party components, or AI-assisted edits—regularly misuse React's useMemo by passing a non-function as the first argument, which can lead to silent bugs or runtime TypeErrors that are surprisingly hard to trace. TypeScript and ESLint don't always catch these mistakes because of any/generics, generated code, or runtime-only patterns, so the problem affects a slice of the 25 million professional developers who collectively represent a roughly $3.3B tooling market ($132/year per dev). The downstream cost is time spent debugging, flaky CI, and poorer developer experience on internal platforms and product teams. You could build a DEV-only runtime diagnostics library that patches or wraps React's useMemo in development builds to detect non-function first arguments and emit high-fidelity warnings with file/line context and a suggested codemod or one-click fix. Pair that with an ESLint rule, an automated fixer, and optional CI/editor integrations so teams get immediate runtime signal plus a static remediation path. Market timing is favorable: rising JS complexity, broader TypeScript adoption that still leaves runtime gaps, and increased copy/paste from AI tools create demand for complementary runtime checks; the market score is 88/100 and revenue potential 78/100, and competition is medium. To stand out, focus on very low-noise, high-precision diagnostics, an open-source core to build trust, and paid CI/enterprise features (telemetry, enforcement, auto-fix); be honest about challenges—maintaining compatibility across React versions and avoiding false positives in advanced higher-order patterns will require careful engineering and ongoing maintenance.