After upgrading from version 8 to 9, some of my multi-line formatted commands have broken.

Reproduction:

import {$} from "execa";

try {
  // 404 is just a stupid way to get an error for some details.
  // Some commands are large, so I break them up by escaping newlines in templates:
  //   https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals#multi-line_strings
  await $`404 abc\
  def`;
} catch (error) {
  console.log("command", error.command); // 404 abc  ef
  console.log("escaped", error.escapedCommand); // 404 "abc " ef
}

Expected command: 404 abc def or something close enough
Actual commands: 404 abc ef or 404 "abc " ef

I suspect it may be related to the difference between the template strings and the raw strings passed to a tag function. Example:

function poo(foo, ...bar) {
  console.log("strings", foo.slice());
  console.log("raw", foo.raw);
}

poo`404 abc def`;
poo`404 abc
  def`;
poo`404 abc\
  def`;

In the first two examples, the raw strings and the strings arrays match up.

strings (1) ['404 abc def']
raw (1) ['404 abc def']

strings (1) ['404 abc
  def']
raw (1) ['404 abc
  def']

In the 3rd sample however the generated strings and the raw strings are different.

strings (1) ['404 abc  def']
raw (1) ['404 abc\\
  def']

I suspect there may be some code that may be mixing up the raw strings with the regular strings causing some of the escaping to be offset by a character. But that is just a theory 🤷.