fix: validate article summary extracted path input

src/summary_mcp/runtime/article_summary_jobs.py

@@ -76,6 +76,17 @@ def _load_result(job_id: str) -> dict[str, Any] | None:
     return json.loads(path.read_text(encoding="utf-8-sig"))
 
 
+def _validate_article_summary_extracted_path(extracted_path: Path) -> None:
+    if not extracted_path.exists():
+        raise FileNotFoundError(f"extracted_path does not exist: {extracted_path}")
+    if extracted_path.is_dir():
+        raise ValueError(
+            "extracted_path must be a JSON file, not a directory. "
+            "Pass a single extracted file like outputs/freshrss/rerun/<run-id>/extracted/item-01.extracted.json, "
+            "or a batch extracted JSON file."
+        )
+
+
 def start_article_summary_job(
     *,
     extracted_path: Path,
@@ -87,8 +98,7 @@ def start_article_summary_job(
     llm_model: str | None = None,
     llm_api_url: str | None = None,
 ) -> dict[str, Any]:
-    if not extracted_path.exists():
-        raise FileNotFoundError(f"extracted_path does not exist: {extracted_path}")
+    _validate_article_summary_extracted_path(extracted_path)
     if not selected_ids:
         raise ValueError("selected_ids must not be empty")
 
@@ -166,8 +176,7 @@ def run_article_summary_job(*, job_id: str) -> dict[str, Any]:
         extracted_path = Path(input_payload["extracted_path"])
         output_dir = Path(input_payload["output_dir"])
         selected_ids = list(input_payload["selected_ids"])
-        if not extracted_path.exists():
-            raise FileNotFoundError(f"extracted_path does not exist: {extracted_path}")
+        _validate_article_summary_extracted_path(extracted_path)
         if not selected_ids:
             raise ValueError("selected_ids must not be empty")
         store.finish_stage(