fix: stop test scripts from inheriting the terminal

Scripts inherited the TUI's terminal as stdin, so a tool like flutter
could switch it back to line mode with echo on exit. Mouse events then
printed as raw escape codes and shortcuts stopped working.

Author: bananaplain

render_machine/render_utils.py

@@ -109,6 +109,7 @@ def execute_script(  # noqa: C901
     start_time = time.time()
     proc = subprocess.Popen(
         cmd,
+        stdin=subprocess.DEVNULL,
         stdout=subprocess.PIPE,
         stderr=subprocess.STDOUT,
         text=True,

tests/test_execute_script.py

@@ -0,0 +1,44 @@
+"""Tests for running test scripts with render_utils.execute_script."""
+
+import os
+import stat
+import sys
+from pathlib import Path
+
+import pytest
+
+from render_machine.render_utils import execute_script
+
+
+@pytest.fixture
+def stdin_with_input():
+    """Replace fd 0 with a pipe holding a line, as a terminal would after a keypress.
+
+    A pipe stands in for the terminal: whether a script can reach codeplain's stdin
+    does not depend on what kind of file stdin is, and a pipe works in CI too.
+    """
+    read_fd, write_fd = os.pipe()
+    os.write(write_fd, b"keypress\n")
+    os.close(write_fd)
+    # A child process inherits file descriptor 0, not sys.stdin, so fd 0 is what has to change.
+    saved_stdin = os.dup(0)
+    os.dup2(read_fd, 0)
+    os.close(read_fd)
+    yield
+    os.dup2(saved_stdin, 0)
+    os.close(saved_stdin)
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="shell scripts are not supported on Windows")
+def test_script_does_not_inherit_stdin(tmp_path: Path, stdin_with_input):
+    # A tool such as flutter resets the terminal it reads from, which breaks the TUI.
+    # The script reports what it finds on its stdin: the waiting line if it inherited
+    # codeplain's stdin, end-of-file if it was given an empty one.
+    script = tmp_path / "read_stdin.sh"
+    script.write_text('#!/bin/sh\nif read -r line; then echo "read:$line"; else echo "eof"; fi\n')
+    script.chmod(script.stat().st_mode | stat.S_IEXEC)
+
+    returncode, output, _ = execute_script(str(script), [], "Unit Tests")
+
+    assert returncode == 0
+    assert output.strip() == "eof"