Fix 'default' model selection breaking readiness indicator

When a user selected the 'Default' option in Settings, the dropdown
sent an empty string "" to the backend. The route saved it as a DB row,
which caused get_setting() to return "" instead of falling back to
Config defaults. The chat status endpoint then tried to match "" against
installed model names — always failing — resulting in model: "not_found"
and a permanently failing readiness indicator.

services/settings.py:
- Add delete_setting() helper: removes a setting row so get_setting()
  correctly falls back to its hardcoded default argument

routes/settings.py:
- Import delete_setting
- When default_model or intent_model are saved as empty string, delete
  the DB row instead of storing "" — cleanly restores Config fallback

routes/chat.py:
- chat_status_route: add explicit `or Config.OLLAMA_MODEL` guard for
  any existing "" rows written before this fix (migration safety net)
- send_message and summarize routes: same guard on model resolution
  so empty settings never cause silent generation failures

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/fabledassistant/routes/chat.py

@@ -135,7 +135,7 @@ async def send_message_route(conv_id: int):
         if msg.role != "system":
             history.append({"role": msg.role, "content": msg.content})
 
-    model = conv.model or await get_setting(uid, "default_model", Config.OLLAMA_MODEL)
+    model = conv.model or await get_setting(uid, "default_model", Config.OLLAMA_MODEL) or Config.OLLAMA_MODEL
 
     # Launch background generation task (context building happens inside the task)
     asyncio.create_task(run_generation(
@@ -257,7 +257,7 @@ async def summarize_conversation_route(conv_id: int):
     conv = await get_conversation(uid, conv_id)
     if conv is None:
         return jsonify({"error": "Conversation not found"}), 404
-    model = conv.model or await get_setting(uid, "default_model", Config.OLLAMA_MODEL)
+    model = conv.model or await get_setting(uid, "default_model", Config.OLLAMA_MODEL) or Config.OLLAMA_MODEL
     try:
         note = await summarize_conversation_as_note(uid, conv_id, model)
         return jsonify(note), 201
@@ -319,6 +319,9 @@ async def chat_status_route():
     """Check Ollama availability, model installation, and model load state."""
     uid = get_current_user_id()
     default_model = await get_setting(uid, "default_model", Config.OLLAMA_MODEL)
+    # Guard against empty-string rows written by older code when user selected "default"
+    if not default_model:
+        default_model = Config.OLLAMA_MODEL
     result = {
         "ollama": "unavailable",
         "model": "not_found",

src/fabledassistant/routes/settings.py

@@ -4,7 +4,7 @@ from fabledassistant.auth import login_required, get_current_user_id
 from fabledassistant.config import Config
 from fabledassistant.services.caldav import CALDAV_SETTING_KEYS, get_caldav_config, test_connection
 from fabledassistant.services.llm import get_installed_models
-from fabledassistant.services.settings import get_all_settings, set_settings_batch
+from fabledassistant.services.settings import delete_setting, get_all_settings, set_settings_batch
 
 settings_bp = Blueprint("settings", __name__, url_prefix="/api/settings")
 
@@ -33,7 +33,20 @@ async def update_settings_route():
                 if installed and model not in installed:
                     return jsonify({"error": f"Model '{model}' is not installed"}), 400
 
-    await set_settings_batch(uid, {k: str(v) for k, v in data.items()})
+    # Empty string for model keys means "reset to system default".
+    # Delete the DB row so get_setting() falls back to Config defaults
+    # rather than returning "" and breaking model resolution everywhere.
+    _MODEL_KEYS = frozenset({"default_model", "intent_model"})
+    to_save = {}
+    for k, v in data.items():
+        str_v = str(v)
+        if k in _MODEL_KEYS and not str_v:
+            await delete_setting(uid, k)
+        else:
+            to_save[k] = str_v
+
+    if to_save:
+        await set_settings_batch(uid, to_save)
     settings = await get_all_settings(uid)
     return jsonify(settings)
 

src/fabledassistant/services/settings.py

@@ -1,6 +1,6 @@
 import logging
 
-from sqlalchemy import select
+from sqlalchemy import delete as sa_delete, select
 
 from fabledassistant.models import async_session
 from fabledassistant.models.setting import Setting
@@ -46,6 +46,15 @@ async def set_settings_batch(user_id: int, settings: dict[str, str]) -> None:
     logger.info("Batch-updated %d settings for user %d", len(settings), user_id)
 
 
+async def delete_setting(user_id: int, key: str) -> None:
+    """Remove a setting row so get_setting() returns its hardcoded default instead."""
+    async with async_session() as session:
+        await session.execute(
+            sa_delete(Setting).where(Setting.user_id == user_id, Setting.key == key)
+        )
+        await session.commit()
+
+
 async def get_all_settings(user_id: int) -> dict[str, str]:
     async with async_session() as session:
         result = await session.execute(