Mara's decision on #4179: the default window for comments/timeline (no
flags at all) is now the newest 10, matching an explicit --tail 10 --
agent can still opt into the old oldest-first window via an explicit
--limit. Same restructure in both verbs: limit u64 -> Option<u64>, only
the explicit-limit branch takes the head path now, the tail-or-default
branch covers both --tail N and the no-flags case.
timeline.rs also gets the real fix: TimelineListHeaders.x_total_count is
a genuine field forgejo-api already returns on every timeline call --
verified against the vendored crate source. The old 'no total exists'
premise in the module doc was false, same shape as #3200. Replaced the
over-fetch-by-one boolean 'more' with an exact count via a cheap
page_size=1 fetch_total, mirroring comments.rs's fetch_tail pagination
math for --tail. JSON output reshaped to {events, more_before,
more_after, since_more, since_limit_clamped}, matching comments.rs --
a breaking interface change, intentional.
Also fixed a real pre-existing bug in comments.rs's truncation_note:
the more_before message suggested retrying with --tail, which is
nonsensical since more_before only ever fires from a tail-shaped
window. Now correctly suggests --limit. Added a regression test.
fixes#4179
1be4b81f65