Add multilingual language and systems learning tracks

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+<!doctype html><html lang="en"><meta charset="utf-8"><title>Regression tests must challenge the fix</title><h1>Regression tests must challenge the fix</h1><p>15-minute session: read for 3 minutes, trace for 3, experiment for 7, and complete the check for 2. Spend longer whenever you need.</p><p>Write a test that fails before a bug fix and passes afterward. Include the smallest input that reproduces the issue and a neighboring valid case. Keep authorization, boundary, and error-path tests; a happy-path screenshot is not sufficient. Document what your test cannot prove and avoid claiming absence of all vulnerabilities.</p><p><strong>Practice and evidence:</strong> Predict the example or draw its state transitions. Change one assumption, test the boundary, and record the actual result. Explain what this small model does not establish about a production system.</p><h3>Practice and evidence</h3><p>Keep three notes: your prediction, the actual result, and why they match or differ. The completion check grades understanding; the practice task builds skill.</p></html>