waitForShellPrompt(on:within:)

Keys sent before that are echoed with no prompt in front of them, which leaves the prompt to land on the row the command's own output wants. A case looking for a row equal to what it printed is then waiting for something that cannot arrive, and reports it as a timeout naming nothing. One capture settles it for every case that follows.

What the prompt *says* is not portable — sh is dash on Linux and bash on macOS, which prints sh-3.2$ — so readiness is that the pane has drawn anything at all. Until the shell starts it has drawn nothing.

This reads the pane directly rather than through the wait machinery: a fixture that bootstrapped itself with the code under test would make every unrelated case depend on it.