Fog means “no line event recorded yet at this position.” It is not proof that code is untested. Whole run shows the static union of recorded line events; the separate coverage report still measures executable statements and branch alternatives.
Playback uses event order, not real-time speed. The all-process view merges observations by the machine's monotonic clock. It does not establish causality between threads or processes. Select a thread to follow its own sequence. Call, return and exception markers are Python trace events; generator suspension also produces return/call markers.
Recording covers the configured project Python source, including newly launched Python subprocesses. Native code, generated code with synthetic filenames, pre-existing processes, and threads started outside Python's threading module are outside this capture. Source is snapshotted when recorded; variables and return values are not stored.
Tracing changes timing. An event cap or abruptly killed process can leave an incomplete recording; those cases are flagged above. Trace runs are exploratory, and ordinary tests remain the correctness check.