fix: resolve 13 Pylance type-checking warnings

- test_e2e.py: initialize steps/result before polling loop to avoid possibly-unbound
- test_rag_quality.py: add assert _collection is not None after initialization (3 sites)
- validation/base.py: filename param typed Optional[str] instead of str
- validation/run_validation.py: capture getenv result to avoid str|None assignment

src/backend/test_e2e.py

@@ -25,6 +25,8 @@ async def main():
         print(f"Submitted case: {case_id}")
 
         # Poll until done
+        steps: list = []
+        result: dict = {}
         for i in range(60):  # up to 5 minutes
             await asyncio.sleep(5)
             r = await client.get(f"{API}/api/cases/{case_id}")

src/backend/test_rag_quality.py

@@ -242,6 +242,7 @@ async def rebuild_chroma(persist_dir: str):
     from app.tools.guideline_retrieval import GuidelineRetrievalTool
     tool = GuidelineRetrievalTool()
     await tool._ensure_initialized()
+    assert tool._collection is not None, "Collection failed to initialize"
     count = tool._collection.count()
     print(f"  Rebuilt collection with {count} guidelines")
     return tool
@@ -252,6 +253,7 @@ async def show_stats(persist_dir: str):
     from app.tools.guideline_retrieval import GuidelineRetrievalTool
     tool = GuidelineRetrievalTool()
     await tool._ensure_initialized()
+    assert tool._collection is not None, "Collection failed to initialize"
 
     count = tool._collection.count()
     print(f"\n  Collection: clinical_guidelines")
@@ -371,6 +373,7 @@ async def main():
         from app.tools.guideline_retrieval import GuidelineRetrievalTool
         tool = GuidelineRetrievalTool()
         await tool._ensure_initialized()
+        assert tool._collection is not None, "Collection failed to initialize"
         count = tool._collection.count()
         print(f"\n  Collection has {count} documents")
         if count == 0:

src/backend/validation/base.py

@@ -297,7 +297,7 @@ def clear_checkpoint(dataset: str) -> None:
 # Final results save
 # ──────────────────────────────────────────────
 
-def save_results(summary: ValidationSummary, filename: str = None):
+def save_results(summary: ValidationSummary, filename: Optional[str] = None):
     """Save validation results to JSON."""
     RESULTS_DIR.mkdir(parents=True, exist_ok=True)
 

src/backend/validation/run_validation.py

@@ -32,8 +32,9 @@ if str(BACKEND_DIR) not in sys.path:
 # Load .env and export HF_TOKEN so huggingface_hub picks it up
 from dotenv import load_dotenv
 load_dotenv(BACKEND_DIR / ".env")
-if os.getenv("HF_TOKEN"):
-    os.environ["HF_TOKEN"] = os.getenv("HF_TOKEN")
+hf_token = os.getenv("HF_TOKEN")
+if hf_token:
+    os.environ["HF_TOKEN"] = hf_token
 
 from validation.base import (
     ValidationSummary,