Two scroll-state bugs cause the viewport to snap to the bottom after
streaming completes, even when the user has scrolled up to read:
1. _scrollAfterMessageRender (ui.js): when preserveScroll=true and
_scrollPinned=true (re-set by the 250px near-bottom hysteresis),
_followMessagesAfterDomReplace() calls scrollToBottom(), overriding
the user's position. Added !_messageUserUnpinned guard so explicitly
scrolled-up users get their snapshot restored instead.
2. _finishDone (messages.js): the explicit scrollToBottom() at L3302
fires when shouldFollowOnDone is true, but that flag only checks a
120px near-bottom threshold. Added _isMessagePaneNearBottom(250)
gate so users reading 250px+ above bottom keep their position.
Also adds a new 'auto_scroll_follow' setting (default: off) that gates
scrollIfPinned() and _shouldFollowMessagesOnDomReplace(). When disabled,
the viewport never auto-scrolls during streaming — the user controls
scroll position manually and uses the ↓ button to jump to bottom.
7-file setting-add pattern applied:
- api/config.py: _SETTINGS_DEFAULTS + _SETTINGS_BOOL_KEYS
- static/boot.js: both init paths
- static/ui.js: scrollIfPinned() + _shouldFollowMessagesOnDomReplace()
- static/index.html: checkbox in appearance settings
- static/i18n.js: en + zh-CN translations
- static/panels.js: payload, autosave, populate, full save
- messages.js: no additional changes (gated via _shouldFollowMessagesOnDomReplace)
Tests updated: test_tars_scroll_reset_regressions, test_issue1690,
test_issue3545. All 116 scroll-related tests pass.
e05b99b7fd
