Desktop notifications never write to the TUI terminal

pyproject.toml

@@ -19,6 +19,7 @@ dependencies = [
     "bashlex==0.18",
     "pathspec==1.1.1",
     "notify-py==0.3.43",
+    "jeepney==0.9.0; sys_platform == 'linux'",
     "pyperclip==1.11.0",
     "watchdog==6.0.0",
     "setproctitle==1.3.7",

src/toad/setting_choices.py

@@ -6,9 +6,11 @@
 from dataclasses import dataclass
 from typing import ClassVar
 from random import choice
+from threading import Lock
 from textual.content import Content
 from toad.widgets.future_text import FutureText
 
+import toad
 from agent_comms.declared_family import DeclaredFamily
 from toad.setting_declarations import Choice
 
@@ -96,24 +98,90 @@ def shown(cls, count: int) -> bool:
         return False
 
 
+class DesktopService:
+    """The platform's notification service, as notifypy detects it."""
+
+    def notification(self):
+        from notifypy import Notify
+
+        return Notify()
+
+    def send(self, app, notification) -> DesktopService:
+        notification.send()
+        return self
+
+
+class DBusDesktop(DesktopService):
+    """notifypy's notify-send path inherits Toad's terminal as stderr; its D-Bus
+    notifier starts no child process that could write over the TUI."""
+
+    def notification(self):
+        from notifypy import Notify
+        from notifypy.os_notifiers.linux import LinuxNotifier
+
+        return Notify(use_custom_notifier=LinuxNotifier)
+
+
+class UncheckedDBusDesktop(DBusDesktop):
+    """Asks the session bus once whether anything serves notifications, because
+    notifypy's D-Bus notifier reports an error reply as a delivery."""
+
+    name: ClassVar[str] = "org.freedesktop.Notifications"
+
+    def send(self, app, notification) -> DesktopService:
+        return self.served(app).send(app, notification)
+
+    def served(self, app) -> DesktopService:
+        from jeepney import DBusAddress, new_method_call
+        from jeepney.io.blocking import open_dbus_connection
+
+        bus = DBusAddress("/org/freedesktop/DBus", bus_name="org.freedesktop.DBus",
+                          interface="org.freedesktop.DBus")
+        try:
+            with open_dbus_connection(bus="SESSION") as connection:
+                owned = connection.send_and_get_reply(
+                    new_method_call(bus, "NameHasOwner", "s", (self.name,)), timeout=2).body[0]
+                activatable = self.name in connection.send_and_get_reply(
+                    new_method_call(bus, "ListActivatableNames"), timeout=2).body[0]
+        except OSError:
+            owned = activatable = False
+        if owned or activatable:
+            return DBusDesktop()
+        app.call_from_thread(
+            app.notify,
+            "Desktop notifications are off for this session: no notification daemon is running.",
+            severity="warning",
+        )
+        return AbsentDesktop()
+
+
+class AbsentDesktop(DesktopService):
+    """Nothing serves notifications; asking again per message only fails again."""
+
+    def send(self, app, notification) -> DesktopService:
+        return self
+
+
 class NotificationPolicy(Choice, DeclaredFamily, affix="Notification"):
+    desktop: ClassVar[DesktopService] = UncheckedDBusDesktop() if toad.os == "linux" else DesktopService()
+    sending: ClassVar[Lock] = Lock()
+
     @classmethod
     def deliver(cls, app, message: str, *, title: str = "", sound: str | None = None) -> None:
         """Shared delivery belongs to the policy that admits it."""
         if not cls.enabled(app.app_focus):
             return
         from importlib.resources import files
-        from notifypy import Notify
-        import toad
 
-        notification = Notify()
+        notification = cls.desktop.notification()
         notification.message = message
         notification.title = title
         notification.application_name = "🐸 Toad" if toad.os == "macos" else "Toad"
         if sound and app.settings.notifications.enable_sounds:
             notification.audio = str(files("toad.data").joinpath(f"sounds/{sound}.wav"))
         notification.icon = str(files("toad.data").joinpath("images/frog.png"))
-        notification.send()
+        with cls.sending:
+            NotificationPolicy.desktop = NotificationPolicy.desktop.send(app, notification)
 
     @classmethod
     @abstractmethod