refactor: centralize progress reporters, default user-agent, improve error propagation and aria2 fetch usage

core/progress.py

@@ -41,3 +41,24 @@ def report_progress(
         progress_callback(payload)
     except Exception as e:
         log.debug(f"{error_context} failed: {e}")
+
+
+def get_progress_reporter(error_context: str) -> Callable[[Optional[Callable[[Dict[str, Any]], None]], str, str, Optional[float]], None]:
+    """Return a closure for reporting progress with a pre-configured error context."""
+    def reporter(
+        progress_callback: Optional[Callable[[Dict[str, Any]], None]],
+        stage: str,
+        message: str,
+        percent: Optional[float] = None,
+        **extra: Any,
+    ) -> None:
+        report_progress(
+            progress_callback,
+            stage,
+            message,
+            percent,
+            error_context=error_context,
+            **extra,
+        )
+    return reporter
+