feat(assistant): a question opens in the AI assistant chosen, Proton's Lumo by default

Questions asked from the app went to Claude alone. Settings › Assistant
now chooses where they open (decided 2026-10-14): Lumo, the default, by
its guest chat with the question in the address's fragment (Lumo's
`prefill`, which needs no account and reaches no server; the address for
one's own account loses the question when nobody is signed in), ChatGPT,
Claude, Mistral, Perplexity, Duck.ai, Grok, Kagi Assistant, HuggingChat,
or an address of one's own with %s. Each link fills the question in for
the person to send (Perplexity answers at once, Grok asks first); Gemini,
which has no such link, and Copilot, whose stopped working, are left out.
The field names the assistant ("Ask Lumo…"). A device that sent questions
to Claude goes on asking an assistant, now Lumo. Connecting Claude to read
studysets stays as it was.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/test/core/device_settings/device_settings_bloc_test.dart

@@ -89,7 +89,7 @@ void main() {
     expect(store.writes, [after]);
   });
 
-  test('asking Claude, turned on, keeps the rest and is kept', () async {
+  test('asking an assistant, turned on, keeps the rest and is kept', () async {
     final store = MemoryDeviceSettingsStore();
     final bloc = DeviceSettingsBloc(
       store,
@@ -103,7 +103,7 @@ void main() {
     expect(store.writes, [after]);
   });
 
-  test('a copy for another choice keeps asking Claude', () {
+  test('a copy for another choice keeps asking an assistant', () {
     const before = DeviceSettings(assistant: true);
 
     expect(before.withAppearance(Appearance.light).assistant, isTrue);

halkyon_learn_flutter/test/core/device_settings/device_settings_store_test.dart

@@ -56,7 +56,7 @@ void main() {
   });
 
   test(
-    "doesn't ask Claude until turned on, then keeps it, and the rest",
+    "doesn't ask an assistant until turned on, then keeps it, and the rest",
     () async {
       expect((await store.read()).assistant, isFalse);
 
@@ -70,15 +70,18 @@ void main() {
     },
   );
 
-  test('keeps where questions go and the search engine, its own address '
-      'too', () async {
+  test('keeps where questions go, the assistant and the search engine, '
+      'their own addresses too', () async {
     final first = await store.read();
-    expect(first.assistantTarget, AssistantTarget.claude);
+    expect(first.assistantTarget, AssistantTarget.assistant);
+    expect(first.aiAssistant, isNull);
     expect(first.searchEngine, isNull);
 
     await store.write(
       const DeviceSettings(
         assistantTarget: AssistantTarget.web,
+        aiAssistant: 'custom',
+        customAssistantUrl: 'https://chat.example.org/?q=%s',
         searchEngine: 'custom',
         customSearchUrl: 'https://search.example.org/?q=%s',
       ),
@@ -86,10 +89,21 @@ void main() {
 
     final read = await FileDeviceSettingsStore(file).read();
     expect(read.assistantTarget, AssistantTarget.web);
+    expect(read.aiAssistant, 'custom');
+    expect(read.customAssistantUrl, 'https://chat.example.org/?q=%s');
     expect(read.searchEngine, 'custom');
     expect(read.customSearchUrl, 'https://search.example.org/?q=%s');
   });
 
+  test('questions a device sent to Claude, the only assistant before, go to '
+      'the assistant chosen', () async {
+    file.writeAsStringSync('{"assistant": true, "assistantTarget": "claude"}');
+
+    final read = await FileDeviceSettingsStore(file).read();
+    expect(read.assistantTarget, AssistantTarget.assistant);
+    expect(read.aiAssistant, isNull);
+  });
+
   test('keeps a return to the device language', () async {
     await store.write(const DeviceSettings(language: 'en-US'));
     await store.write(const DeviceSettings(appearance: Appearance.light));