fix: initialize readline before capture

CHANGELOG.md

@@ -7,6 +7,8 @@ releases are available on [PyPI](https://pypi.org/project/pytask) and
 
 ## Unreleased
 
+- [#969](https://github.com/pytask-dev/pytask/pull/969) initializes readline before
+  output capture so libedit-backed interactive prompts and debuggers remain responsive.
 - [#971](https://github.com/pytask-dev/pytask/pull/971) restores help text for
   PDB commands wrapped by pytask.
 - [#970](https://github.com/pytask-dev/pytask/pull/970) prevents tee-sys capture from

src/_pytask/capture.py

@@ -99,9 +99,21 @@ def pytask_parse_config(config: dict[str, Any]) -> None:
     config["show_capture"] = convert_to_enum(config["show_capture"], ShowCapture)
 
 
+def _readline_workaround() -> None:
+    """Import readline before it can attach to redirected standard streams.
+
+    GNU readline is not affected, but libedit can retain the file descriptors that are
+    active when it is first imported. Importing it before capture starts keeps
+    interactive input and debugging responsive on affected Python installations.
+    """
+    with contextlib.suppress(ImportError):
+        import readline  # noqa: F401, PLC0415
+
+
 @hookimpl
 def pytask_post_parse(config: dict[str, Any]) -> None:
     """Initialize the CaptureManager."""
+    _readline_workaround()
     pluginmanager = config["pm"]
     capman = CaptureManager(config["capture"])
     pluginmanager.register(capman, "capturemanager")

tests/test_capture.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import builtins
 import contextlib
 import io
 import os
@@ -31,6 +32,37 @@
     from collections.abc import Generator
 
 
+def test_readline_workaround_ignores_missing_module(monkeypatch):
+    imported_modules = []
+    original_import = builtins.__import__
+
+    def import_or_raise(name, *args, **kwargs):
+        imported_modules.append(name)
+        if name == "readline":
+            raise ImportError
+        return original_import(name, *args, **kwargs)
+
+    monkeypatch.setattr(builtins, "__import__", import_or_raise)
+
+    capture._readline_workaround()
+
+    assert imported_modules == ["readline"]
+
+
+def test_readline_workaround_runs_before_capture_starts(monkeypatch):
+    events = []
+    capman = Mock()
+    capman.start_capturing.side_effect = lambda: events.append("capture")
+    monkeypatch.setattr(
+        capture, "_readline_workaround", lambda: events.append("readline")
+    )
+    monkeypatch.setattr(capture, "CaptureManager", lambda _method: capman)
+
+    capture.pytask_post_parse({"pm": Mock(), "capture": CaptureMethod.FD})
+
+    assert events == ["readline", "capture"]
+
+
 @pytest.mark.parametrize("show_capture", ["s", "no", "stdout", "stderr", "log", "all"])
 def test_show_capture(tmp_path, runner, show_capture):
     source = """

tests/test_debugging.py

@@ -114,6 +114,27 @@ def import_module(name):
     assert issubclass(wrapped, CustomPdb)
 
 
+@pytest.mark.skipif(not IS_PEXPECT_INSTALLED, reason="pexpect is not installed.")
+@pytest.mark.skipif(sys.platform == "win32", reason="pexpect cannot spawn on Windows.")
+def test_pdb_after_readline_is_imported_during_capture(tmp_path):
+    source = """
+    from pathlib import Path
+
+    def task_example():
+        import readline
+
+        breakpoint()
+        Path(__file__).with_name("continued.txt").touch()
+    """
+    tmp_path.joinpath("task_module.py").write_text(textwrap.dedent(source))
+
+    child = pexpect.spawn(f"pytask {tmp_path.as_posix()}")
+    child.expect("Pdb")
+    child.sendline("continue")
+    _flush(child)
+    assert tmp_path.joinpath("continued.txt").exists()
+
+
 @pytest.mark.skipif(not IS_PEXPECT_INSTALLED, reason="pexpect is not installed.")
 @pytest.mark.skipif(sys.platform == "win32", reason="pexpect cannot spawn on Windows.")
 def test_post_mortem_on_error_w_kwargs(tmp_path):