The STREAM_DONE keep-open exception (#4970 round 6/7) was scoped to PINNED
followers only, on the assumption that unpinned readers 'preserve their viewport
normally'. That holds on desktop (overflow-anchor:none + JS snapshot restore) but
NOT on mobile.
Repro (isolated debug instance + CDP touch emulation, faithful to a real phone):
a reader who scrolls UP to read inside the just-settled turn is UNPINNED. At
STREAM_DONE the live worklog/thinking cards collapse into a compact summary,
shrinking the transcript by hundreds of px ABOVE their viewport. On mobile the
CSS resting value is overflow-anchor:auto, but _fixMobileScrollJank() flips an
inline overflow-anchor:none over the settle render — so native scroll-anchoring
is suppressed during exactly the frame the unpinned reader needs it to absorb the
above-viewport shrink. The content then leaps to the top of the latest turn (the
'往回大跳' report). Single-variable measurement: collapse-with-auto shifts the
reader 0px; collapse-with-none shifts -248px.
Fix: keep the just-settled worklog open for BOTH pin states (still one-shot
scoped to the turn that just settled, so historical worklogs still collapse
compact). This removes the shrink entirely, fixing the jump for every
device/anchor-mode instead of fighting the anchor engine. The #4856 guard and the
mobile overflow-anchor:auto CSS are untouched, so Boev's Android DOM-wipe fix and
akrhin's #MOBILESCROLL fix both stay intact.
- Rename _shouldKeepSettledWorklogOpenForPinnedFollow ->
_shouldKeepSettledWorklogOpenForStreamSettle (drops the _scrollPinned /
_messageUserUnpinned gate; keeps the one-shot stream-id token).
- Update the #4970 behavioral regression test to assert keep-open is TRUE for the
armed turn under BOTH pin states, FALSE for historical turns and after disarm.
d9622bf9b0
