fix(cli): make Alt+Enter insert a newline on LF-as-Enter terminals

On terminals that send a bare LF for plain Enter (WSL is the case
prompt_toolkit itself calls out), Alt+Enter arrives as ESC + LF
("\x1b\x0a" = Escape + ControlJ), not the ESC + CR the existing
"escape","enter" binding matches. The Escape was swallowed and the bare
LF hit prompt_toolkit's default submit, so the documented "universally
supported" Alt+Enter newline fallback failed on exactly the terminal path
plain Enter is preserved for.

Bind ESC + ControlJ to insert a newline too, and add a real-PromptSession
regression test covering the WSL Alt+Enter path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

nanobot/cli/commands.py

@@ -346,7 +346,16 @@ def _build_cli_key_bindings() -> KeyBindings:
     def _(event):
         event.current_buffer.validate_and_handle()
 
-    @kb.add("escape", "enter")  # Alt+Enter / Meta+Enter
+    @kb.add("escape", "enter")  # Alt+Enter / Meta+Enter (ESC + CR, "\x1b\r")
+    def _(event):
+        event.current_buffer.insert_text("\n")
+
+    # On the same LF-as-Enter terminals (WSL) we preserve plain Enter for,
+    # Alt+Enter arrives as ESC + LF ("\x1b\x0a" = Escape + ControlJ) rather than
+    # ESC + CR, so the "escape","enter" binding above never matches: Escape is
+    # swallowed and the bare LF triggers prompt_toolkit's default submit. Bind
+    # ESC + ControlJ too so Alt+Enter reliably inserts a newline there as well.
+    @kb.add("escape", Keys.ControlJ)  # Alt+Enter on LF-as-Enter terminals
     def _(event):
         event.current_buffer.insert_text("\n")
 

tests/cli/test_cli_input.py

@@ -140,6 +140,29 @@ async def test_xterm_modifyotherkeys_shift_enter_inserts_newline():
     assert result == "foo\nbar"
 
 
+@pytest.mark.asyncio
+async def test_alt_enter_inserts_newline_on_lf_terminals():
+    """On LF-as-Enter terminals (WSL), Alt+Enter arrives as ESC + LF
+    ("\\x1b\\x0a" = Escape + ControlJ) rather than the ESC + CR that the
+    "escape","enter" binding matches. Without a dedicated ESC + ControlJ
+    binding the Escape is swallowed and the bare LF submits, so the documented
+    Alt+Enter newline fallback breaks on exactly the terminal path plain Enter
+    is preserved for. Drive a real PromptSession to prove it inserts a newline.
+    """
+    from prompt_toolkit.application import create_app_session
+    from prompt_toolkit.input import create_pipe_input
+    from prompt_toolkit.output import DummyOutput
+
+    with create_pipe_input() as pipe_input:
+        with create_app_session(input=pipe_input, output=DummyOutput()):
+            commands._init_prompt_session()
+            session = commands._PROMPT_SESSION
+            pipe_input.send_text("foo\x1b\x0abar\r")
+            result = await session.prompt_async("> ")
+
+    assert result == "foo\nbar"
+
+
 def test_thinking_spinner_pause_stops_and_restarts():
     """Pause should stop the active spinner and restart it afterward."""
     spinner = MagicMock()