fix(cli): keep prompt stable and flush stale arrow-key input

nanobot/cli/commands.py

@@ -1,7 +1,10 @@
 """CLI commands for nanobot."""
 
 import asyncio
+import os
 from pathlib import Path
+import select
+import sys
 
 import typer
 from rich.console import Console
@@ -18,6 +21,40 @@ app = typer.Typer(
 console = Console()
 
 
+def _flush_pending_tty_input() -> None:
+    """Drop unread keypresses typed while the model was generating output."""
+    try:
+        fd = sys.stdin.fileno()
+        if not os.isatty(fd):
+            return
+    except Exception:
+        return
+
+    try:
+        import termios
+
+        termios.tcflush(fd, termios.TCIFLUSH)
+        return
+    except Exception:
+        pass
+
+    try:
+        while True:
+            ready, _, _ = select.select([fd], [], [], 0)
+            if not ready:
+                break
+            if not os.read(fd, 4096):
+                break
+    except Exception:
+        return
+
+
+def _read_interactive_input() -> str:
+    """Read user input with a stable prompt for terminal line editing."""
+    console.print("[bold blue]You:[/bold blue] ", end="")
+    return input()
+
+
 def version_callback(value: bool):
     if value:
         console.print(f"{__logo__} nanobot v{__version__}")
@@ -318,7 +355,8 @@ def agent(
         async def run_interactive():
             while True:
                 try:
-                    user_input = console.input("[bold blue]You:[/bold blue] ")
+                    _flush_pending_tty_input()
+                    user_input = _read_interactive_input()
                     if not user_input.strip():
                         continue
                     

tests/test_cli_input_minimal.py

@@ -0,0 +1,37 @@
+import builtins
+
+import nanobot.cli.commands as commands
+
+
+def test_read_interactive_input_uses_plain_input(monkeypatch) -> None:
+    captured: dict[str, object] = {}
+
+    def fake_print(*args, **kwargs):
+        captured["printed"] = args
+        captured["print_kwargs"] = kwargs
+
+    def fake_input(prompt: str = "") -> str:
+        captured["prompt"] = prompt
+        return "hello"
+
+    monkeypatch.setattr(commands.console, "print", fake_print)
+    monkeypatch.setattr(builtins, "input", fake_input)
+
+    value = commands._read_interactive_input()
+
+    assert value == "hello"
+    assert captured["prompt"] == ""
+    assert captured["print_kwargs"] == {"end": ""}
+    assert captured["printed"] == ("[bold blue]You:[/bold blue] ",)
+
+
+def test_flush_pending_tty_input_skips_non_tty(monkeypatch) -> None:
+    class FakeStdin:
+        def fileno(self) -> int:
+            return 0
+
+    monkeypatch.setattr(commands.sys, "stdin", FakeStdin())
+    monkeypatch.setattr(commands.os, "isatty", lambda _fd: False)
+
+    commands._flush_pending_tty_input()
+