perf(llm): route background tasks to dedicated model to preserve KV cache

Background tasks (title generation, tag suggestions, project summaries,
RSS classification) were using qwen3:8b and wiping its KV cache after
every response, preventing prefix cache hits on subsequent user messages.

Adds OLLAMA_BACKGROUND_MODEL (default: qwen2.5:0.5b) config var and
routes all background LLM calls to it, keeping qwen3:8b's KV cache
warm between user messages for consistent sub-second TTFT.

Also adds infinite scroll to KnowledgeView (replaces load-more button)
and bakes spaCy en_core_web_sm into the Docker image to eliminate the
pip install on every startup.

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

src/fabledassistant/app.py

@@ -249,6 +249,7 @@ def create_app() -> Quart:
         # Also ensure the embedding model is pulled (no warm needed).
         asyncio.create_task(_warm_user_models())
         asyncio.create_task(_pull_model(Config.EMBEDDING_MODEL, warm=False))
+        asyncio.create_task(_pull_model(Config.OLLAMA_BACKGROUND_MODEL, warm=False))
 
         # After models are pulled, backfill embeddings for existing notes.
         # Runs in the background so it never blocks the server from accepting requests.

src/fabledassistant/config.py

@@ -24,6 +24,10 @@ class Config:
     )
     OLLAMA_URL: str = os.environ.get("OLLAMA_URL", "http://localhost:11434")
     OLLAMA_MODEL: str = os.environ.get("OLLAMA_MODEL", "qwen3:latest")
+    # Lightweight model for background tasks (title generation, tag suggestions,
+    # project summaries, RSS classification). Using a separate model keeps the
+    # main model's KV cache intact between user messages, enabling prefix cache hits.
+    OLLAMA_BACKGROUND_MODEL: str = os.environ.get("OLLAMA_BACKGROUND_MODEL", "qwen2.5:0.5b")
     # KV cache context window for generation. Keep this as small as practical —
     # a larger context forces more KV cache into CPU RAM, drastically slowing prefill.
     # 16384 covers ~30+ message conversations with our system prompt comfortably.

src/fabledassistant/services/chat.py

@@ -238,7 +238,7 @@ async def save_response_as_note(user_id: int, message_id: int) -> dict:
                 },
                 {"role": "user", "content": msg.content[:2000]},
             ]
-            title = await generate_completion(prompt_messages, model)
+            title = await generate_completion(prompt_messages, Config.OLLAMA_BACKGROUND_MODEL)
             title = title.strip().strip('"\'').strip()[:100]
         except Exception:
             logger.warning("Failed to generate note title, using fallback", exc_info=True)

src/fabledassistant/services/generation_task.py

@@ -138,7 +138,7 @@ async def _generate_title(messages: list[dict], model: str) -> str:
         },
         {"role": "user", "content": "\n\n".join(conv_lines)},
     ]
-    title = await generate_completion(prompt_messages, model, max_tokens=30)
+    title = await generate_completion(prompt_messages, Config.OLLAMA_BACKGROUND_MODEL, max_tokens=30)
     title = title.strip().strip('"\'').strip()
     return title[:100] if title else ""
 

src/fabledassistant/services/projects.py

@@ -122,7 +122,7 @@ async def generate_project_summary(user_id: int, project_id: int) -> None:
         from fabledassistant.services.llm import generate_completion
         from fabledassistant.config import Config
         messages = [{"role": "user", "content": prompt}]
-        summary = await generate_completion(messages, model=Config.OLLAMA_MODEL, max_tokens=400)
+        summary = await generate_completion(messages, model=Config.OLLAMA_BACKGROUND_MODEL, max_tokens=400)
         if not summary:
             return
 

src/fabledassistant/services/rss_classifier.py

@@ -64,7 +64,7 @@ async def classify_items_batch(
         return {}
 
     if model is None:
-        model = Config.OLLAMA_MODEL
+        model = Config.OLLAMA_BACKGROUND_MODEL
 
     vocab = STANDARD_TOPICS + [t for t in user_include_topics if t not in STANDARD_TOPICS]
     items_block = "\n".join(

src/fabledassistant/services/tag_suggestions.py

@@ -7,7 +7,6 @@ import re
 from fabledassistant.config import Config
 from fabledassistant.services.llm import generate_completion
 from fabledassistant.services.notes import get_all_tags
-from fabledassistant.services.settings import get_setting
 
 logger = logging.getLogger(__name__)
 
@@ -22,7 +21,7 @@ async def suggest_tags(user_id: int, title: str, body: str, current_tags: list[s
         return []
 
     existing_tags = await get_all_tags(user_id)
-    model = await get_setting(user_id, "default_model", Config.OLLAMA_MODEL)
+    model = Config.OLLAMA_BACKGROUND_MODEL
 
     existing_list = ", ".join(f"#{t}" for t in existing_tags) if existing_tags else "(none yet)"