logging: add opt-in quiet_vips_logging() helper

pyvips redirects all GLib messages ("VIPS: threadpool completed ..."
per operation) onto the 'pyvips' logger at INFO. The helper caps that
logger at WARNING while keeping 'pyvips.voperation' (deprecated-argument
notices) at INFO. Library import remains free of logging side effects;
the CLI and worker entry points call the helper instead of their old
bare setLevel, which also hid the deprecation notices.

mediapreview/__main__.py

@@ -32,15 +32,14 @@ from docopt import docopt
 
 from mediapreview.backends import dispatch
 from mediapreview.exceptions import PreviewError
-from mediapreview.util.logformat import EmojiFormatter
+from mediapreview.util.logformat import EmojiFormatter, quiet_vips_logging
 
 
 def _configure_logging() -> None:
     handler = logging.StreamHandler(sys.stderr)
     handler.setFormatter(EmojiFormatter())
     logging.basicConfig(level=logging.INFO, handlers=[handler])
-    # pyvips is chatty at INFO ("threadpool completed ..." per operation).
-    logging.getLogger("pyvips").setLevel(logging.WARNING)
+    quiet_vips_logging()
 
 
 def _oosetup(name: str) -> None:

mediapreview/util/logformat.py

@@ -31,3 +31,18 @@ class EmojiFormatter(logging.Formatter):
 
     def format(self, record: logging.LogRecord) -> str:
         return format_level_prefix(record.levelno) + record.getMessage()
+
+
+def quiet_vips_logging() -> None:
+    """Silence libvips per-operation chatter without hiding deprecations.
+
+    pyvips redirects every GLib message ("VIPS: threadpool completed ...")
+    onto the ``pyvips`` logger at INFO; cap that logger at WARNING. pyvips's
+    own diagnostics (e.g. deprecated-argument notices) are logged on the
+    ``pyvips.voperation`` child logger and stay at the default INFO.
+
+    Opt-in: applications that want quiet vips output call this once during
+    their own logging setup. mediapreview never calls it on import.
+    """
+    logging.getLogger("pyvips").setLevel(logging.WARNING)
+    logging.getLogger("pyvips.voperation").setLevel(logging.INFO)

mediapreview/worker.py

@@ -40,7 +40,7 @@ except ImportError:  # pragma: no cover - optional worker extra
 from mediapreview.backends import dispatch
 from mediapreview.exceptions import PreviewError
 from mediapreview.protocol import PreviewRequest, PreviewResponse
-from mediapreview.util.logformat import format_level_prefix
+from mediapreview.util.logformat import format_level_prefix, quiet_vips_logging
 
 logger = logging.getLogger(__name__)
 
@@ -171,8 +171,7 @@ def main() -> None:
     handler = logging.StreamHandler(sys.stderr)
     handler.setFormatter(_WorkerLogFormatter())
     logging.basicConfig(level=logging.INFO, handlers=[handler])
-    # pyvips is chatty at INFO ("threadpool completed ..." per operation).
-    logging.getLogger("pyvips").setLevel(logging.WARNING)
+    quiet_vips_logging()
     # NOTE: standalone package no longer depends on cista config loading.
     # Consumers can load their own configuration before starting workers.
     if len(sys.argv) > 1: