Per sub-project-2 plan Task 4 / spec §5.1. derive_tags(Probe) -> Tags with the
attached_pic cover-art guard so an art-bearing audio file stays mode=audio.
Duration falls back to the longest stream when format.duration is absent, and
rounds half-up so 12.5s -> 13s (Python's round() would give 12 via banker's
rounding) to match the spec's stated behavior.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Ben Stull
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