_loadOlderMessages() previously fetched older messages with the legacy
index-cursor page (msg_before=_oldestIdx&msg_limit=30) and prepended
the page to S.messages. After #2716 the backend always runs the full
append-only merge for /api/session?messages=1 — the same merge as a
larger msg_limit on the same call — so we can ask for a larger
authoritative tail window directly instead of stitching pages on the
client.
Behavior
* Default request shape becomes msg_limit=currentLoaded+30. The newly
exposed head of the response is what the user sees as 'older
messages'. No new query parameters.
* msg_before remains supported by the backend and is retained in the
client as a race-fallback path: if the returned tail no longer has
the currently displayed messages as a suffix (because the session
appended new messages mid-flight, or merge filtered something), the
client issues the legacy msg_before page and prepends it instead.
This preserves correctness under concurrent appends.
* Suffix-continuity uses the existing _sameTranscriptMessage helper,
which tolerates timestamp drift and content-array reshapes.
* Existing race guards (loadingSessionId, S.session.session_id, and
the _messagesGeneration snapshot from #1937) are reapplied after
the fallback await.
Tests
Updated four static-string assertions in the existing scroll/viewport
tests to track the new mutation site (S.messages = nextMessages) and
the new msg_limit=requestedLimit shape, while still asserting that
msg_before remains in the body for the race-fallback path.
pytest -q
tests/test_older_history_viewport_preservation.py
tests/test_parallel_session_switch.py
tests/test_issue1937_endless_scroll_jumpstart_race.py
tests/test_session_tail_payload.py
-> 52 passed
node --check static/sessions.js -> ok
Notes
Originally part of PR #2835. That PR was closed because of an
architectural conflict with #2716 on a different file (api/models.py
metadata-only path). #2716 left static/sessions.js untouched — this
change applies cleanly on post-#2716 master with no rebase work.
nesquena APPROVED 2026-05-22. Cherry-picked onto post-v0.51.127
master via 3-way apply. Resolved api/routes.py conflict: master had
the inline correctness fix from the deep-review iteration; PR
refactors it into _metadata_only_message_summary() helper. Took the
helper AND added profile= threading (post-#2827 master adds
profile-aware state.db reads). Kept master's pre-existing
test_api_session_reload_drops_stale_cached_user_tail_after_saved_assistant
alongside the PR's new test_metadata_fast_path_matches_reconciliation_for_restamped_replays.
Co-authored-by: dobby-d-elf <dobby.the.agent@gmail.com>
When _loadOlderMessages prepends older messages, the viewport snaps
to the bottom instead of staying where the user was.
Two bugs compounding:
1. Wrong scrollable container. Code used `$("msgInner")` for scrollHeight
and scrollTop, but #msgInner has no overflow-y — it is a flex column.
The actual scrollable container is #messages (`.messages{overflow-y:auto}`).
Setting msgInner.scrollTop was silently ignored.
2. renderMessages calls scrollToBottom at the end (ui.js:2552),
which unconditionally scrolls #messages to the bottom and sets
_scrollPinned=true. Since bug #1 made the scroll-restore a no-op,
the page landed at the bottom every time.
Fix:
- Changed scroll restore target from `$("msgInner")` to `$("messages")`.
- Reset _scrollPinned = false after restoring the user position,
so scrollToBottom does not re-fire on next tick.
Qi