fix(wizard): read keypresses from the raw fd so arrow keys work

sys.stdin.read(1) on the buffered TextIOWrapper pulls the whole escape
sequence into its Python-level buffer, so the follow-up select() sees an
empty fd and every arrow/Home/End press degrades to bare Esc; the unread
'[B' tail then leaks into the next keypress. Read raw bytes via os.read()
and select() on the file descriptor instead, keeping the same key tokens
and classifications. Add pty-driven regression tests over a real cbreak
terminal covering CSI sequences, single-byte keys, bare Esc, and tail-leak.

src/weekly_activity/wizard.py

@@ -343,23 +343,26 @@ def _read_keypress() -> str:
     """Read one keystroke from stdin (cbreak mode); classify it."""
     import select
 
-    char = sys.stdin.read(1)
+    fd = sys.stdin.fileno()
-    if char == "\x1b":
+    # Read raw bytes from the fd: a buffered text read would pull the whole
+    # escape sequence into its own buffer, leaving nothing for select to see.
+    first = os.read(fd, 1)
+    if first == b"\x1b":
         # A bare Esc is not followed by more bytes; CSI sequences are. Peek briefly.
-        readable, _, _ = select.select([sys.stdin], [], [], 0.05)
+        readable, _, _ = select.select([fd], [], [], 0.05)
         if not readable:
             return _KEY_ESCAPE
-        tail = sys.stdin.read(2)
+        tail = os.read(fd, 2)
-        return _CSI_KEYS.get(tail, _KEY_OTHER)
+        return _CSI_KEYS.get(tail.decode("ascii", "replace"), _KEY_OTHER)
-    if char in ("\r", "\n"):
+    if first in (b"\r", b"\n"):
         return _KEY_ENTER
-    if char == "\x01":  # Ctrl-A
+    if first == b"\x01":  # Ctrl-A
         return _KEY_HOME
-    if char == "\x05":  # Ctrl-E
+    if first == b"\x05":  # Ctrl-E
         return _KEY_END
-    if char == "k":
+    if first == b"k":
         return _KEY_UP
-    if char == "j":
+    if first == b"j":
         return _KEY_DOWN
     return _KEY_OTHER
 

tests/test_wizard.py

@@ -2,8 +2,16 @@
 
 from __future__ import annotations
 
+from collections.abc import Callable
 import io
+import os
+from pathlib import Path
+import pty
+import re
+import select
+import subprocess
 import sys
+import time
 import unittest
 from unittest import mock
 
@@ -54,5 +62,145 @@ class OptionLineRenderingTest(unittest.TestCase):
         self.assertEqual(_option_line("Remove a source", False), "  Remove a source")
 
 
+_CHILD_SCRIPT = """
+import os
+import sys
+import termios
+import tty
+
+sys.path.insert(0, os.environ["WIZARD_SRC"])
+from weekly_activity.wizard import _read_keypress  # noqa: E402
+
+fd = sys.stdin.fileno()
+saved = termios.tcgetattr(fd)
+tty.setcbreak(fd)
+try:
+    for _ in range(int(sys.argv[1])):
+        print("READY", flush=True)
+        print(f"KEY={_read_keypress()}", flush=True)
+finally:
+    termios.tcsetattr(fd, termios.TCSADRAIN, saved)
+"""
+
+
+_KEY_LINE = re.compile(rb"KEY=([a-z]+)\r\n")
+
+
+class ArrowKeyKeypressTest(unittest.TestCase):
+    """CSI sequences must classify over a real pty instead of surfacing as bare Esc.
+
+    Drives the genuine ``_read_keypress()`` on a cbreak-mode terminal — the path the
+    arrow-key menu uses, unreachable through scripted ``io.StringIO`` stdin.
+    """
+
+    TIMEOUT_S = 20.0
+
+    def _await(
+        self,
+        master: int,
+        child: subprocess.Popen[bytes],
+        box: dict[str, bytes],
+        condition: Callable[[], bool],
+        stage: str,
+    ) -> None:
+        """Block until ``condition`` holds on the pty stream, else fail loudly."""
+        deadline = time.monotonic() + self.TIMEOUT_S
+        while not condition():
+            remaining = deadline - time.monotonic()
+            if remaining <= 0:
+                break
+            readable, _, _ = select.select([master], [], [], min(remaining, 0.2))
+            if readable:
+                try:
+                    chunk = os.read(master, 4096)
+                except OSError:  # slave closed: the child exited early
+                    break
+                if chunk:
+                    box["stream"] += chunk
+        else:
+            return
+        if child.poll() is None:
+            child.kill()
+            child.wait(timeout=5)
+        err = child.stderr.read().decode("utf-8", "replace") if child.stderr else ""
+        self.fail(f"{stage}: stalled; tail={box['stream'][-300:]!r} stderr={err!r}")
+
+    def _child_tokens(self, sends: list[bytes]) -> list[str]:
+        """Send each payload after its READY prompt; return printed key tokens."""
+        src_dir = str(Path(__file__).resolve().parents[1] / "src")
+        master, slave = pty.openpty()
+        child = subprocess.Popen(
+            [sys.executable, "-c", _CHILD_SCRIPT, str(len(sends))],
+            stdin=slave,
+            stdout=slave,
+            stderr=subprocess.PIPE,
+            env={**os.environ, "WIZARD_SRC": src_dir},
+        )
+        os.close(slave)
+        box: dict[str, bytes] = {"stream": b""}
+
+        try:
+            tokens: list[str] = []
+            for index, payload in enumerate(sends):
+                self._await(
+                    master,
+                    child,
+                    box,
+                    lambda i=index: box["stream"].count(b"READY") > i,
+                    f"READY prompt {index} before {payload!r}",
+                )
+                seen = len(_KEY_LINE.findall(box["stream"]))
+                os.write(master, payload)
+                self._await(
+                    master,
+                    child,
+                    box,
+                    lambda n=seen: len(_KEY_LINE.findall(box["stream"])) > n,
+                    f"token line after {payload!r}",
+                )
+                tokens.append(_KEY_LINE.findall(box["stream"])[-1].decode())
+
+            self.assertEqual(
+                box["stream"].count(b"READY"),
+                len(sends),
+                f"unexpected output tail {box['stream'][-300:]!r}",
+            )
+            self.assertEqual(len(_KEY_LINE.findall(box["stream"])), len(sends))
+            try:
+                child.wait(timeout=self.TIMEOUT_S)
+            except subprocess.TimeoutExpired:
+                child.kill()
+                child.wait()
+                self.fail("child ignored termination after completing every keystroke")
+            err = child.stderr.read().decode("utf-8", "replace") if child.stderr else ""
+            self.assertEqual(child.returncode, 0, err)
+            return tokens
+        finally:
+            if child.poll() is None:
+                child.kill()
+                child.wait()
+            if child.stderr is not None:
+                child.stderr.close()
+            os.close(master)
+
+    def test_arrow_home_end_sequences_map_to_selection_keys(self) -> None:
+        tokens = self._child_tokens([b"\x1b[A", b"\x1b[B", b"\x1b[H", b"\x1b[F"])
+        self.assertEqual(tokens, ["up", "down", "home", "end"])
+
+    def test_single_byte_keystrokes_still_classify(self) -> None:
+        # The reader switched to raw fd bytes; letters/Enter must classify as before.
+        tokens = self._child_tokens([b"\r", b"k", b"j", b"x"])
+        self.assertEqual(tokens, ["enter", "up", "down", "other"])
+
+    def test_bare_escape_is_classified_as_escape(self) -> None:
+        tokens = self._child_tokens([b"\x1b"])
+        self.assertEqual(tokens, ["escape"])
+
+    def test_escape_sequence_tail_does_not_leak_into_next_keypress(self) -> None:
+        # The original report: an arrow press poisoned the following reads.
+        tokens = self._child_tokens([b"\x1b[B", b"j", b"\r"])
+        self.assertEqual(tokens, ["down", "down", "enter"])
+
+
 if __name__ == "__main__":
     unittest.main()