fix(onboard): allow empty strings and falsy values in input fields

Fixes two related input-handling bugs in the onboard wizard:

1. _input_text treated "" as None, preventing users from clearing
   optional string fields or entering empty strings intentionally.

2. _input_model_with_autocomplete used `if value else None`, which
   discarded falsy values such as empty strings or 0.

To support clearing optional string fields, add _is_str_or_none() and
normalize empty strings to None inside _configure_pydantic_model only
when the field annotation is `str | None`. Required str fields keep
"" as a valid value.

Also included:
- Remember last selected item in provider/channel/model menus for
  better UX when configuring multiple items.
- Rename _SIMPLE_TYPES and _MENU_DISPATCH to lowercase to follow
  Python naming conventions (they are local variables, not constants).
- Remove unused imports in test file.

Extracted from PR #3358.

nanobot/cli/onboard.py

@@ -191,13 +191,13 @@ def _get_field_type_info(field_info) -> FieldTypeInfo:
             origin = get_origin(annotation)
             args = get_args(annotation)
 
-    _SIMPLE_TYPES: dict[type, str] = {bool: "bool", int: "int", float: "float"}
+    _simple_types: dict[type, str] = {bool: "bool", int: "int", float: "float"}
 
     if origin is list or (hasattr(origin, "__name__") and origin.__name__ == "List"):
         return FieldTypeInfo("list", args[0] if args else str)
     if origin is dict or (hasattr(origin, "__name__") and origin.__name__ == "Dict"):
         return FieldTypeInfo("dict", None)
-    for py_type, name in _SIMPLE_TYPES.items():
+    for py_type, name in _simple_types.items():
         if annotation is py_type:
             return FieldTypeInfo(name, None)
     if isinstance(annotation, type) and issubclass(annotation, BaseModel):
@@ -403,7 +403,7 @@ def _input_text(display_name: str, current: Any, field_type: str, field_info=Non
 
     value = _get_questionary().text(f"{display_name}:", default=default).ask()
 
-    if value is None or value == "":
+    if value is None:
         return None
 
     if field_type == "int":
@@ -507,7 +507,7 @@ def _input_model_with_autocomplete(
         qmark=">",
     ).ask()
 
-    return value if value else None
+    return value if value is not None else None
 
 
 def _input_context_window_with_recommendation(
@@ -594,6 +594,15 @@ _FIELD_HANDLERS: dict[str, Any] = {
 }
 
 
+def _is_str_or_none(annotation: Any) -> bool:
+    """Check whether a field annotation is ``str | None`` (or ``Optional[str]``)."""
+    origin = get_origin(annotation)
+    if origin is None:
+        return False
+    args = get_args(annotation)
+    return str in args and type(None) in args
+
+
 def _configure_pydantic_model(
     model: BaseModel,
     display_name: str,
@@ -626,11 +635,20 @@ def _configure_pydantic_model(
             items.append(f"{display}: {formatted}")
         return items + ["[Done]"]
 
+    last_field_name: str | None = None
     while True:
         console.clear()
         _show_config_panel(display_name, working_model, fields)
         choices = get_choices()
-        answer = _select_with_back("Select field to configure:", choices)
+        default_choice = None
+        if last_field_name:
+            for idx, (fname, _) in enumerate(fields):
+                if fname == last_field_name:
+                    default_choice = choices[idx]
+                    break
+        answer = _select_with_back(
+            "Select field to configure:", choices, default=default_choice
+        )
 
         if answer is _BACK_PRESSED or answer is None:
             return None
@@ -641,6 +659,8 @@ def _configure_pydantic_model(
         if field_idx < 0 or field_idx >= len(fields):
             return None
 
+        last_field_name = fields[field_idx][0]
+
         field_name, field_info = fields[field_idx]
         current_value = getattr(working_model, field_name, None)
         ftype = _get_field_type_info(field_info)
@@ -697,6 +717,10 @@ def _configure_pydantic_model(
         else:
             new_value = _input_with_existing(field_display, current_value, ftype.type_name, field_info=field_info)
         if new_value is not None:
+            # Normalize empty string to None for optional string fields so that
+            # clearing an api_key / api_base actually removes the value.
+            if new_value == "" and _is_str_or_none(field_info.annotation):
+                new_value = None
             setattr(working_model, field_name, new_value)
 
 
@@ -795,12 +819,23 @@ def _configure_providers(config: Config) -> None:
                 choices.append(display)
         return choices + ["<- Back"]
 
+    last_provider_key: str | None = None
     while True:
         try:
             console.clear()
             _show_section_header("LLM Providers", "Select a provider to configure API key and endpoint")
             choices = get_provider_choices()
-            answer = _select_with_back("Select provider:", choices)
+            default_choice = None
+            if last_provider_key:
+                display = _get_provider_names().get(last_provider_key)
+                if display:
+                    for c in choices:
+                        if c.replace(" *", "") == display:
+                            default_choice = c
+                            break
+            answer = _select_with_back(
+                "Select provider:", choices, default=default_choice
+            )
 
             if answer is _BACK_PRESSED or answer is None or answer == "<- Back":
                 break
@@ -812,6 +847,7 @@ def _configure_providers(config: Config) -> None:
             # Find the actual provider key from display names
             for name, display in _get_provider_names().items():
                 if display == provider_name:
+                    last_provider_key = name
                     _configure_provider(config, name)
                     break
 
@@ -885,17 +921,21 @@ def _configure_channels(config: Config) -> None:
     channel_names = list(_get_channel_names().keys())
     choices = channel_names + ["<- Back"]
 
+    last_choice: str | None = None
     while True:
         try:
             console.clear()
             _show_section_header("Chat Channels", "Select a channel to configure connection settings")
-            answer = _select_with_back("Select channel:", choices)
+            answer = _select_with_back(
+                "Select channel:", choices, default=last_choice
+            )
 
             if answer is _BACK_PRESSED or answer is None or answer == "<- Back":
                 break
 
             # Type guard: answer is now guaranteed to be a string
             assert isinstance(answer, str)
+            last_choice = answer
             _configure_channel(config, answer)
         except KeyboardInterrupt:
             console.print("\n[dim]Returning to main menu...[/dim]")
@@ -1073,6 +1113,7 @@ def run_onboard(initial_config: Config | None = None) -> OnboardResult:
     original_config = base_config.model_copy(deep=True)
     config = base_config.model_copy(deep=True)
 
+    last_main_choice: str | None = None
     while True:
         console.clear()
         _show_main_menu_header()
@@ -1092,6 +1133,7 @@ def run_onboard(initial_config: Config | None = None) -> OnboardResult:
                     "[S] Save and Exit",
                     "[X] Exit Without Saving",
                 ],
+                default=last_main_choice,
                 qmark=">",
             ).ask()
         except KeyboardInterrupt:
@@ -1105,7 +1147,7 @@ def run_onboard(initial_config: Config | None = None) -> OnboardResult:
                 return OnboardResult(config=original_config, should_save=False)
             continue
 
-        _MENU_DISPATCH = {
+        _menu_dispatch = {
             "[P] LLM Provider": lambda: _configure_providers(config),
             "[C] Chat Channel": lambda: _configure_channels(config),
             "[H] Channel Common": lambda: _configure_general_settings(config, "Channel Common"),
@@ -1121,6 +1163,7 @@ def run_onboard(initial_config: Config | None = None) -> OnboardResult:
         if answer == "[X] Exit Without Saving":
             return OnboardResult(config=original_config, should_save=False)
 
-        action_fn = _MENU_DISPATCH.get(answer)
+        action_fn = _menu_dispatch.get(answer)
         if action_fn:
+            last_main_choice = answer
             action_fn()

tests/agent/test_onboard_logic.py

@@ -4,7 +4,6 @@ These tests focus on the business logic behind the onboard wizard,
 without testing the interactive UI components.
 """
 
-import json
 from pathlib import Path
 from types import SimpleNamespace
 from typing import Any, cast
@@ -13,18 +12,15 @@ import pytest
 from pydantic import BaseModel, Field
 
 from nanobot.cli import onboard as onboard_wizard
-
-# Import functions to test
 from nanobot.cli.commands import _merge_missing_defaults
 from nanobot.cli.onboard import (
     _BACK_PRESSED,
     _configure_pydantic_model,
     _format_value,
+    _get_constraint_hint,
     _get_field_display_name,
     _get_field_type_info,
-    _get_constraint_hint,
     _input_text,
-    _validate_field_constraint,
     run_onboard,
 )
 from nanobot.config.schema import Config
@@ -960,3 +956,121 @@ class TestMainMenuUpdate:
 
         assert result.should_save is True
         assert pause_called["n"] == 1
+
+
+class TestInputTextEmptyString:
+    """Tests for _input_text empty-string handling bug fix."""
+
+    def test_empty_string_returned_not_none(self, monkeypatch):
+        """_input_text should return empty string, not None, when user enters ''."""
+        monkeypatch.setattr(
+            onboard_wizard,
+            "_get_questionary",
+            lambda: SimpleNamespace(text=lambda *a, **kw: SimpleNamespace(ask=lambda: "")),
+        )
+
+        result = _input_text("Name", "old", "str")
+        assert result == ""
+
+    def test_none_still_returns_none(self, monkeypatch):
+        """_input_text should return None when questionary returns None."""
+        monkeypatch.setattr(
+            onboard_wizard,
+            "_get_questionary",
+            lambda: SimpleNamespace(text=lambda *a, **kw: SimpleNamespace(ask=lambda: None)),
+        )
+
+        result = _input_text("Name", "old", "str")
+        assert result is None
+
+
+class TestIsStrOrNone:
+    """Tests for _is_str_or_none helper."""
+
+    def test_str_or_none_true(self):
+        from nanobot.cli.onboard import _is_str_or_none
+
+        assert _is_str_or_none(str | None) is True
+
+    def test_optional_str_true(self):
+        from typing import Optional
+        from nanobot.cli.onboard import _is_str_or_none
+
+        assert _is_str_or_none(Optional[str]) is True
+
+    def test_str_only_false(self):
+        from nanobot.cli.onboard import _is_str_or_none
+
+        assert _is_str_or_none(str) is False
+
+    def test_int_or_none_false(self):
+        from nanobot.cli.onboard import _is_str_or_none
+
+        assert _is_str_or_none(int | None) is False
+
+
+class TestConfigurePydanticModelEmptyString:
+    """Tests that optional string fields are cleared when empty string is entered."""
+
+    def test_optional_str_empty_string_becomes_none(self, monkeypatch):
+        """Entering '' for an optional str field should set it to None."""
+        from pydantic import BaseModel
+        from nanobot.cli.onboard import _is_str_or_none
+
+        class M(BaseModel):
+            api_key: str | None = None
+
+        model = M(api_key="secret")
+
+        call_count = {"select": 0}
+
+        def fake_select(_prompt, choices, default=None):
+            call_count["select"] += 1
+            # First call: select the api_key field, then Done
+            if call_count["select"] == 1:
+                for c in choices:
+                    if "Api Key" in c:
+                        return c
+                return choices[0]
+            return "[Done]"
+
+        monkeypatch.setattr(onboard_wizard, "_select_with_back", fake_select)
+        monkeypatch.setattr(onboard_wizard, "_show_config_panel", lambda *a, **kw: None)
+        # Simulate user entering empty string
+        monkeypatch.setattr(
+            onboard_wizard, "_input_with_existing", lambda *a, **kw: ""
+        )
+
+        result = _configure_pydantic_model(model, "Test")
+        assert result is not None
+        assert result.api_key is None
+
+    def test_required_str_empty_string_kept(self, monkeypatch):
+        """Entering '' for a required str field should keep the empty string."""
+        from pydantic import BaseModel
+
+        class M(BaseModel):
+            api_key: str = ""
+
+        model = M(api_key="secret")
+
+        call_count = {"select": 0}
+
+        def fake_select(_prompt, choices, default=None):
+            call_count["select"] += 1
+            if call_count["select"] == 1:
+                for c in choices:
+                    if "Api Key" in c:
+                        return c
+                return choices[0]
+            return "[Done]"
+
+        monkeypatch.setattr(onboard_wizard, "_select_with_back", fake_select)
+        monkeypatch.setattr(onboard_wizard, "_show_config_panel", lambda *a, **kw: None)
+        monkeypatch.setattr(
+            onboard_wizard, "_input_with_existing", lambda *a, **kw: ""
+        )
+
+        result = _configure_pydantic_model(model, "Test")
+        assert result is not None
+        assert result.api_key == ""