Where Did the Interference Go? Eleven Quantum Paradoxes Worked Out with Amplitudes and Records

A computational tutorial on standard quantum probability, written in the language of complex amplitudes (“arrows”) and environmental records. Eleven well-known puzzles — two-path interference, the quantum eraser, delayed choice, the Zeno effect and interaction-free measurement, decoherence, Bell–CHSH, GHZ, Hardy’s argument, the Peres–Mermin square, no-signalling and the information–disturbance trade-off — are each worked out explicitly, step by step. For every example the paper separates three things that are often merged: what quantum theory predicts, which classical model (with which assumptions) is excluded, and what is left to interpretation. A further worked example shows that one and the same loss of interference can leave records whose accessible which-path information ranges from none to complete, and how the difference can be estimated from data. Reported tests of higher-order interference are collected with their original uncertainty conventions. Every computed number is reproduced by released, seeded Python scripts; expected results were fixed (with SHA-256 hashes) before each script was run. The scripts, expected-result files and an independent reviewer’s cross-check are attached to this record and embedded in the PDF. No new physical law or quantum algorithm is claimed; the contribution is a connected, verifiable teaching path.