The source around a breakpoint, numbered, with a mark on the line the page stopped on.

  3 │ export function inspectMe(): number {
  4 │   const answer = 42;
> 5 │   debugger;
  6 │
  7 │   return answer;

Both edges are found rather than counted to. Going up it stops at the line that OPENS the block the breakpoint is in — the function signature, most of the time — because a window that starts mid-statement tells you less than one that starts where the scope does. Going down it stops at the return, since what a function answers is the other half of what you are looking at, and anything past it belongs to a different frame.

Where neither is within reach the limits win, and a return too far away is not shown at all: one line below is enough to see where you are, and four lines of unrelated body is noise.

import { excerpt } from './excerpt.ts';

const plain = { painter: () => (text: string) => text };
excerpt('const a = 1;\ndebugger;\n', 2, plain); // '  1 │ const a = 1;\n> 2 │ debugger;'
excerpt('', 1, plain); // '' — nothing to show is shown as nothing