test(ocr): lock in MetricsPathFilter fail-open behavior

If uvicorn's access log format ever changes (args=None, or shorter
than 3 elements), the filter must keep forwarding records rather than
silently dropping them. Two extra LogRecords cover both edge cases.

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

ocr-service/test_metrics.py

@@ -605,6 +605,29 @@ async def test_ocr_jobs_total_not_incremented_when_pdf_download_fails_in_stream(
     )._value.get() == 0.0
 
 
+def test_uvicorn_access_log_filter_fails_open_on_short_or_missing_args():
+    """The filter must default-allow records when args is None or shorter than expected.
+
+    Locks in fail-open behavior: if uvicorn ever changes its format we keep
+    forwarding records to the handler rather than silently dropping logs.
+    """
+    import logging as _logging
+    from main import MetricsPathFilter
+
+    filt = MetricsPathFilter()
+    none_record = _logging.LogRecord(
+        name="uvicorn.access", level=_logging.INFO, pathname="", lineno=0,
+        msg="some message", args=None, exc_info=None,
+    )
+    short_record = _logging.LogRecord(
+        name="uvicorn.access", level=_logging.INFO, pathname="", lineno=0,
+        msg="%s %s", args=("a", "b"), exc_info=None,
+    )
+
+    assert filt.filter(none_record) is True
+    assert filt.filter(short_record) is True
+
+
 def test_uvicorn_access_log_filter_skips_metrics_path():
     """The MetricsPathFilter drops uvicorn.access log records that target /metrics."""
     import logging as _logging