Trim one take of a beat's call to a span (free).

NOT metered and NOT confirmed: FREE, one call. Trims one take to the span [keepStartSeconds, keepEndSeconds) — "trim this take to <start>–<end>" — snapped to the take's frames and kept as a NEW take linked to it (trimTake); the take itself stays. Never into a spoken line: a span that cuts into a line placed on the take's speech track is refused (trim_cuts_speech), as is a span outside the take, shorter than the shortest a take is trimmed to, or the whole take (trim_span_invalid) — each before anything is queued. The trimmed take is checked again and watched, and plays over the take it came from only if it passes; its cut then plays its real, shorter length. The repair engine does the same on its own when a cut nobody asked for sits at the start or end of an otherwise good take (rule trim_edge, measured in the file: a hard cut or the first frame of a dissolve), and when a speaker's lips run on past the take's last line where nothing is heard (rule trim_overrun: cut half a second after the line as the take says it). Each take's trimBounds says what it may keep. Review or complete only. Requires Idempotency-Key. Scope: story:write.