verify-completenesslisted

# verify-completeness `verify-coherence` only checks that a span stays on ONE topic; `verify-bookends` only inspects the first/last 1.5s of the already-cut clip and is deliberately inward-only. Neither ever re-reads the WHOLE assembled story to confirm the arc still LANDS. A pick whose payoff sits one sentence past the chosen `t1` reads as truncated — the channel's "cut off early" feeling. This gate fills that hole. For each span it shows Claude the assembled arc (the text inside the span's `cuts`, in order) plus a **tail lookahead** — the source lines right after the current end, bounded by the remaining `dmax` headroom — and asks for one verdict: - `complete` — the arc lands; no change. - `needs_more_tail` — the landing is cut off but present in the lookahead; Claude returns `extend_t1`, a source line-end boundary, and the span's `t1` (and last cut's end) are nudged outward to it, capped at `dmax`. - `truncated` — abrupt but not recoverable within the lookahead/budget; flagged, left unchanged. ## Why source coordinates / why here Outward extension is only clean BEFORE `cut-clip`: once a clip is cut, trimmed, and pace-tightened, the clip-local transcript has discarded source timestamps (see `rebase.py`), so re-deriving where to extend in the source would mean re-running the whole trim/tighten sub-chain. Running in source coords right after `bookend-trim` lets any extension flow naturally through cut → trim → tighten. This complements `verify-bookends`, which owns