Withdraw reader keys before tab eviction and persist every shown error

src/toad/app.py

@@ -7,7 +7,6 @@
 from toad.widgets.comms_transfer import Transfers
 import asyncio
 import signal
-import traceback
 import gc
 import sys
 import json
@@ -294,7 +293,7 @@ def _handle_exception(self, error: Exception) -> bool:
         """The mounted application owns escaped handler and worker errors."""
         if not self.screen_stack or not self.screen.is_mounted:
             return super()._handle_exception(error)
-        self.show_error("".join(traceback.format_exception(error)), type(error).__name__)
+        self.show_error(error, type(error).__name__)
         return True
 
     async def on_load(self) -> None:

src/toad/cli.py

@@ -18,7 +18,7 @@ def persist_terminal_failure(error: Exception) -> None:
     from toad import paths
 
     try:
-        path = paths.save_traceback(error, "Terminal_crash")
+        path = paths.save_error(error, "Terminal_crash")
     except OSError as log_error:
         click.echo(f"Unable to save terminal traceback: {log_error}", err=True)
     else:

src/toad/forms/editors.py

@@ -15,6 +15,8 @@
 from python_introspect.validation import validate_annotation_value
 from textual import containers
 from textual.app import ComposeResult
+from textual.message import Message
+from textual.reactive import var
 from textual.validation import Function
 from textual.geometry import Spacing
 from textual.css.scalar import Scalar
@@ -38,15 +40,23 @@
 class ValueEditor(DeclaredViews, EditorWidget):
     """A control that shows one field's value and sends the user's edits to the state.
 
-    The value lives in the ObjectState: the control is painted from it and
-    keeps nothing else. The editor capability binds the field before the native
+    The value lives in the ObjectState: the control is painted from it. Only
+    transient validation feedback lives here. The editor binds the field before the native
     control is initialized: `class BoolEditor(ValueEditor, Checkbox)`.
     """
 
     states_default: ClassVar[bool] = True
     """Whether the field's help should end with its default value."""
 
     field: DeclaredField
+    feedback: var[str] = var("", init=False)
+
+    class Feedback(Message):
+        """Transient validation text for the field's own view, never a crash log."""
+
+        def __init__(self, text: str) -> None:
+            super().__init__()
+            self.text = text
 
     def __init__(self, field: DeclaredField) -> None:
         self.field = field
@@ -81,11 +91,16 @@ def send(self, value: object) -> None:
             self.field.edit(value)
         except (TypeError, ValueError) as error:
             self.refuse(error)
+        else:
+            self.feedback = ""
 
     def refuse(self, error: Exception) -> None:
-        self.app.show_error(error, self.field.label)
+        self.feedback = str(error)
         self.paint()
 
+    def watch_feedback(self, text: str) -> None:
+        self.post_message(self.Feedback(text))
+
 
 class BoolEditor(ValueEditor, FormCheckbox):
     shows = (bool,)

src/toad/forms/form_view.py

@@ -7,15 +7,15 @@
 from formbridge.forms.parameter_form_service import ParameterFormService
 from formbridge.forms.parameter_info_types import DirectDataclassInfo, ParameterInfo
 from objectstate import DottedFieldPath, ObjectState
-from textual import containers, events, lazy
+from textual import containers, events, lazy, on
 from textual.app import ComposeResult
 from textual.content import Content
 from textual.widgets import Static
 from textual.css._style_properties import Edges
 from textual.geometry import Spacing
 from textual.layouts.stream import StreamLayout
 from rich.style import Style
-from ui_theme.scheme import BackgroundColour, ForegroundColour, MutedColour, PrimaryColour, SecondaryColour
+from ui_theme.scheme import BackgroundColour, ErrorColour, ForegroundColour, MutedColour, PrimaryColour, SecondaryColour
 
 from toad.forms.declared_views import DeclaredField, DeclaredViews
 from toad.forms.editors import ValueEditor
@@ -37,6 +37,12 @@ def paint_foreground(self):
         return self.app.colours.colour(MutedColour)
 
 
+class FieldRefusal(FieldHelp):
+    @property
+    def paint_foreground(self):
+        return self.app.colours.colour(ErrorColour)
+
+
 class GroupTitle(WidgetView, Static):
     padding = Spacing(0, 0, 0, 1)
 
@@ -93,6 +99,8 @@ def __init__(self, field: DeclaredField,
         super().__init__(field, included)
         self.editor = ValueEditor.declared_for(field)
         self.title = FieldTitle(field.label)
+        self.refusal = FieldRefusal("", markup=False)
+        self.refusal.display = False
         self.search_text = " ".join(
             DeclaredField(field.state, step).label
             for step in field.state.parameter_structure.ancestors(field.path)
@@ -102,6 +110,13 @@ def compose(self) -> ComposeResult:
         yield self.title
         yield FieldHelp(self.description())
         yield self.editor
+        yield self.refusal
+
+    @on(ValueEditor.Feedback)
+    def show_feedback(self, message: ValueEditor.Feedback) -> None:
+        message.stop()
+        self.refusal.update(message.text)
+        self.refusal.display = bool(message.text)
 
     def description(self) -> Content:
         help = Content.from_markup(self.field.help)

src/toad/paths.py

@@ -60,14 +60,14 @@ def get_project_data(project_path: Checkout) -> Path:
     return project_data_path
 
 
-def save_traceback(error: BaseException, prefix: str) -> Path:
-    """Write ``error``'s traceback to a new file in the log directory."""
+def save_error(error: BaseException, prefix: str) -> Path:
+    """Persist the exception's traceback and chained causes."""
     import traceback
     from toad.acp.agent import generate_datetime_filename
 
     path = get_log() / generate_datetime_filename(prefix, ".txt")
     descriptor = os.open(path, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o600)
-    with os.fdopen(descriptor, "w") as stream:
+    with os.fdopen(descriptor, "w", encoding="utf-8") as stream:
         traceback.print_exception(error, file=stream)
     return path