A single scroll-up during streaming set _messageUserUnpinned=true and
scrollIfPinned() then permanently stopped auto-follow (only scrollToBottom()
cleared it) — a permanent auto-follow lockout even after the user returned to
the bottom. scrollIfPinned() now re-pins, but ONLY when the reader has genuinely
reached the true-bottom tail (<=80px) AND shows no active scroll intent
(wheel/key/touch/non-message), reusing the listener's _nearBottomCount debounce.
Proximity alone (the ~250px nearBottom band) must never re-pin — that is the
#4295 invariant. Restores the listener's <=80px true-bottom gate too.
Co-authored-by: luperrypf <luperrypf@users.noreply.github.com>
Supersedes the v0.51.199 proximity-re-pin (#3330) and the #3250 upward-intent
timeout with a sticky-unpin model (ChatGPT/Claude/Codex behavior): scroll up =
stay put until you return to the bottom or click the scroll-to-bottom control.
Reconciled against the shipped #3330 code: removed the now-dead
_recentMessageUpwardIntent reference from the #3319 rAF retry, kept the
load-time -Infinity intent-init fix, kept the pinned-only >500 catch-up.
Co-authored-by: pamnard <pamnard@users.noreply.github.com>