Debugging

Why mutable default arguments, circular imports, asyncio deadlocks, memory leaks, and encoding bugs are the same shape of problem underneath - a boundary the code assumed was enforced turned out to be permeable - and the observe/narrow/hypothesize/verify loop that finds which one broke.

The classic shared-state trap and the fix.

Diagnosing and breaking import cycles.

`UnicodeDecodeError`, bytes/str confusion, and normalization.

Rounding, `Decimal`, and comparison traps.

"Works on my machine" resolution.

`pdb`/`breakpoint()`, `ipdb`, remote debugging, and logging.

Before/after fixes for common defects.