gh-158955: PyREPL Update changed line planning for WSL

Lib/_pyrepl/unix_console.py

@@ -835,7 +835,7 @@ def __plan_changed_line(
             planned_cells = diff.new_cells
             changed_cell = visible_new_cells[0]
             return LineUpdate(
-                kind="insert_char",
+                kind=("replace_char" if start_x == oldline.width else "insert_char"),
                 y=y,
                 start_cell=start_cell,
                 start_x=start_x,

Lib/test/test_pyrepl/test_unix_console.py

@@ -259,6 +259,27 @@ def test_cursor_back_write(self, _os_write):
         _os_write.assert_any_call(ANY, b"2")
         con.restore()
 
+    def test_insert_char_only_for_midline_insert(self, _os_write):
+        insert_char = b"<insert-char>"
+        events = itertools.chain(
+            code_to_events("1"),
+            [Event(evt="key", data="left", raw=bytearray(b"\x1bOD"))],
+            code_to_events("2"),
+        )
+        _, con = handle_all_events(
+            events,
+            prepare_console=partial(unix_console, ich1=insert_char),
+        )
+        relevant_writes = []
+        for write in _os_write.call_args_list:
+            output = write.args[1]
+            if insert_char in output:
+                relevant_writes.append(insert_char)
+            elif output in {b"1", b"2"}:
+                relevant_writes.append(output)
+        self.assertEqual(relevant_writes, [b"1", insert_char, b"2"])
+        con.restore()
+
     def test_multiline_function_move_up_short_terminal(self, _os_write):
         # fmt: off
         code = (

Misc/NEWS.d/next/Library/2026-10-07-21-54-29.gh-issue-158955.Ey4Iei.rst

@@ -0,0 +1 @@
+Fixed PyREPL rendering on WSL by avoiding the unnecessary INS terminal sequence when appending a character at the end of a line. INS remains used for true mid-line insertions, with regression coverage added.