reduce-nesting

# Reduce Nesting Deep nesting hides bugs in the branches you didn't read. - **Guard clauses** — handle the invalid/edge cases first and return early. The happy path drops to the left margin. - **Invert conditions** — `if (!valid) return;` instead of wrapping the whole body in `if (valid) {...}`. - **Extract** — a nested block doing one thing becomes a named function. - **Replace flag-then-branch** — return the result directly instead of setting a variable to return later. Target: no function deeper than 2-3 levels. If you still need more, the function is doing too much — split it.