The issue-comments endpoint takes no page or limit, so `comments
--since` cut its window client-side from a whole-list response. The
leftover over-fetch-by-one request (`.page_size(limit + 1)`) was a
no-op and the `--limit` clamp to MAX_LIMIT (49) guarded a truncation
check that no longer needs one.
Drop both: `--since T --limit N` now returns N comments. `comments
--json` still emits `since_limit_clamped`, always `false`. `timeline`
is untouched; its endpoint pages and its clamp stays.
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